ASTM E1479-16

Standard Practice for Describing and Specifying Inductively Coupled Plasma Atomic Emission Spectrometers

SIGNIFICANCE AND USE
5.1 This practice describes the essential components of an ICP-AES. The components include excitation/radio-frequency generators, sample introduction systems, spectrometers, detectors, and signal processing and displays. This description allows the user or potential user to gain a cursory understanding of an ICP-AES system. This practice also provides a means for comparing and evaluating various systems, as well as understanding the capabilities and limitations of each instrument.  
5.2 Training—The manufacturer should provide training in safety, basic theory of ICP-AES analysis, operations of hardware and software, and routine maintenance for at least one operator. Training ideally should consist of the basic operation of the instrument at the time of installation, followed by an in-depth course one or two months later. Advanced courses are also offered at several of the important spectroscopy meetings that occur throughout the year as well as by independent training institutes. Several independent consultants are available who can provide training, sometimes at the user's site.
SCOPE
1.1 This practice describes the components of an inductively coupled plasma atomic emission spectrometer (ICP-AES) that are basic to its operation and to the quality of its performance. This practice identifies critical factors affecting accuracy, precision, and sensitivity. It is not the intent of this practice to specify component tolerances or performance criteria, since these are unique for each instrument. A prospective user should consult with the manufacturer before placing an order, to design a testing protocol that demonstrates the instrument meets all anticipated needs.  
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific safety hazard statements are given in Section 13.

General Information

• Status: Published
• Publication Date: 31-Oct-2016
• ICS: 17.180.30 - Optical measuring instruments
• Technical Committee: E01 - Analytical Chemistry for Metals, Ores, and Related Materials
• Drafting Committee: E01.20 - Fundamental Practices

Relations

• Replaces: ASTM E1479-99(2011) - Standard Practice for Describing and Specifying Inductively-Coupled Plasma Atomic Emission Spectrometers
• Effective Date: 01-Nov-2016
• Refers: ASTM E520-08(2023)e1 - Standard Practice for Describing Photomultiplier Detectors in Emission and Absorption Spectrometry
• Effective Date: 01-Apr-2023
• Refers: ASTM E135-20 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jan-2020
• Refers: ASTM E135-19 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2019
• Refers: ASTM E135-16 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2016
• Refers: ASTM E135-15a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jul-2015
• Refers: ASTM E135-15 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-May-2015
• Refers: ASTM E135-14b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Aug-2014
• Refers: ASTM E135-14a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Apr-2014
• Refers: ASTM E135-14 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Feb-2014
• Refers: ASTM E135-13a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Dec-2013
• Refers: ASTM E135-11b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Sep-2011
• Refers: ASTM E135-11a - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Jun-2011
• Refers: ASTM E135-11 - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 15-Jan-2011
• Refers: ASTM E135-10b - Standard Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
• Effective Date: 01-Jul-2010

Overview

ASTM E1479-16 is a widely recognized standard issued by ASTM International, titled “Standard Practice for Describing and Specifying Inductively Coupled Plasma Atomic Emission Spectrometers” (ICP-AES). This document outlines the essential components and configuration of ICP-AES instruments, describing critical factors that impact analytical accuracy, precision, and sensitivity. The standard provides practical guidance for users and purchasers to compare, evaluate, and specify ICP-AES systems in a manner that aligns with their analytical needs.

Designed according to international principles, ASTM E1479-16 supports laboratories, manufacturers, and quality managers in making informed decisions about instrument selection, operation, and maintenance, ensuring the reliability of elemental analysis.

Key Topics

• Essential Components: The standard details the primary subsystems of ICP-AES instruments, including:

  • Excitation/radio-frequency generators
  • Sample introduction systems (e.g., nebulizers, spray chambers, torches)
  • Spectrometers (types and designs)
  • Detectors (PMTs and solid-state arrays)
  • Signal processing and display systems

• System Performance: Explains factors critical to performance, such as:

  • Accuracy, precision, and sensitivity in elemental determinations
  • Influences of torch design, gas flows, and sample matrix on results
  • Capability to analyze a wide range of sample types (aqueous, organic, solid)

• System Evaluation and Comparison: Provides guidance on how to compare ICP-AES instruments on the basis of:

  • Design features and component quality
  • Analytical capabilities and detection limits
  • Suitability for specific applications (e.g., high matrix tolerance, hydride generation)

• Operator Training: Emphasizes the importance of manufacturer-provided training in:

  • Safety procedures
  • Basic and advanced principles of ICP-AES operation
  • Routine maintenance and troubleshooting

• Safety Practices: Addresses the need for laboratories to:

  • Establish appropriate safety and health practices
  • Determine applicability of regulatory limitations
  • Follow specific hazard guidance provided in the standard

Applications

ASTM E1479-16 is crucial for organizations engaged in elemental analysis using ICP-AES, including:

• Analytical Laboratories: Enables informed instrument selection and specification, ensuring systems meet operational and analytical requirements.
• Quality Assurance: Supports protocol development for consistent and reliable results across different instruments and operating environments.
• Purchasing and Procurement: Facilitates objective comparison and evaluation of ICP-AES offers based on standardized criteria.
• Instrument Manufacturers: Provides a reference for product development, customer support, and technical documentation related to ICP-AES systems.
• Education and Training: Acts as a foundation for developing training curricula for laboratory staff and operators.

Industries that benefit from ASTM E1479-16 include environmental monitoring, metallurgy, pharmaceuticals, food safety, and materials science.

Related Standards

Organizations using or specifying ICP-AES instruments may also reference the following ASTM standards for additional guidance:

• ASTM E135: Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials.
• ASTM E520: Practice for Describing Photomultiplier Detectors in Emission and Absorption Spectrometry.
• ASTM E172: Practice for Describing and Specifying the Excitation Source in Emission Spectrochemical Analysis (Withdrawn but of historical interest).

Note: Users should consult instrument manufacturers and referenced standards to ensure compatibility and meet specific analytical requirements.

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Keywords: ASTM E1479-16, ICP-AES, inductively coupled plasma, atomic emission spectrometer, elemental analysis, instrument specification, sample introduction, spectrometry, detector, training, laboratory safety, analytical chemistry standard.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1479 − 16
Standard Practice for
Describing and Specifying Inductively Coupled Plasma
Atomic Emission Spectrometers
This standard is issued under the fixed designation E1479; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E416Practice for Planning and Safe Operation of a Spec-
trochemical Laboratory (Withdrawn 2005)
1.1 This practice describes the components of an induc-
E520Practice for Describing Photomultiplier Detectors in
tively coupled plasma atomic emission spectrometer (ICP-
Emission and Absorption Spectrometry
AES) that are basic to its operation and to the quality of its
performance. This practice identifies critical factors affecting
3. Terminology
accuracy, precision, and sensitivity. It is not the intent of this
3.1 Definitions—For terminology relating to emission
practice to specify component tolerances or performance
spectrometry, refer to Terminology E135.
criteria, since these are unique for each instrument.Aprospec-
tive user should consult with the manufacturer before placing
4. Summary of Practice
an order, to design a testing protocol that demonstrates the
4.1 AnICP-AESisaninstrumentusedtodetermineelemen-
instrument meets all anticipated needs.
talcomposition.Ittypicallyiscomprisedofseveralassemblies
1.2 The values stated in SI units are to be regarded as
including a radio-frequency (RF) generator, an impedance
standard. The values given in parentheses are for information
matchingnetwork(whererequired),aninductioncoil,aplasma
only.
torch,aplasmaignitorsystem,asampleintroductionsystem,a
1.3 This standard does not purport to address all of the
radiant energy gathering optic, an entrance slit and dispersing
safety concerns, if any, associated with its use. It is the
element to sample and isolate wavelengths of light emitted
responsibility of the user of this standard to establish appro-
from the plasma, one or more devices for converting the
priate safety and health practices and determine the applica-
emitted light into an electrical current or voltage, one or more
bility of regulatory limitations prior to use. Specific safety
analog preamplifiers, one or more analog-to-digital
hazard statements are given in Section 13.
converter(s), and a dedicated computer with printer (see Fig.
1 ).
2. Referenced Documents
4.1.1 The sample is introduced into a high-temperature
2.1 ASTM Standards:
(>6000 K) plasma that is formed from the inductive energy
E135Terminology Relating to Analytical Chemistry for
transfer to and subsequent ionization of the gas stream con-
Metals, Ores, and Related Materials
tained in the torch. The torch is mounted centrally in a metal
E158Practice for Fundamental Calculations to Convert
structure,whichiscalledtheloadcoil.Energyisappliedtothe
Intensities into Concentrations in Optical Emission Spec-
load coil by means of an RF generator.
trochemical Analysis (Withdrawn 2004)
4.1.2 Theterminductivelycoupledreferstothefactthatthe
E172Practice for Describing and Specifying the Excitation
physical phenomenon of induction creates a plasma by trans-
SourceinEmissionSpectrochemicalAnalysis(Withdrawn
ferringenergyfromtheloadcoiltothegasstreamthathasbeen
2001)
momentarily preionized by a high voltage ignitor spark that
functions only during plasma ignition.
This practice is under the jurisdiction ofASTM Committee E01 on Analytical
4.2 When material passes through the plasma, it is
ChemistryforMetals,Ores,andRelatedMaterialsandisthedirectresponsibilityof
vaporized, atomized, and partly ionized. The produced atoms
Subcommittee E01.20 on Fundamental Practices.
and ions are excited into an energetically higher state. Free
Current edition approved Nov. 1, 2016. Published December 2016. Originally
approved in 1992. Last previous edition approved in 2011 as E1479–99 (2011).
atoms and ions are excited from their ground states mainly by
DOI: 10.1520/E1479-16.
collision with the major plasma constituents. The excited
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
atoms or ions subsequently decay to a lower energy state and
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
emit photons, some of which pass through the entrance slit of
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
The last approved version of this historical standard is referenced on
www.astm.org. Courtesy of PerkinElmer, Inc., 761 Main Ave., Norwalk, CT 06859.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1479 − 16
FIG. 1 Components of ICP-AES
a spectrometer. Each element emits a unique set of emission generators, sample introduction systems, spectrometers,
lines. Photons of a desired wavelength may be selected from detectors, and signal processing and displays. This description
the ultraviolet and visible spectra by means of a dispersing allows the user or potential user to gain a cursory understand-
element. ingofanICP-AESsystem.Thispracticealsoprovidesameans
4.2.1 Instrumentsmaydetermineelementseithersimultane- for comparing and evaluating various systems, as well as
ously or sequentially. The output of the detector generally is understanding the capabilities and limitations of each instru-
directed to a preamplifier, an analog-to-digital converter, and a ment.
computer which measures and stores a value proportional to
5.2 Training—The manufacturer should provide training in
the electrical current or voltage generated by the detector(s).
safety, basic theory of ICP-AES analysis, operations of hard-
Using blank and known calibration solutions, a calibration
ware and software, and routine maintenance for at least one
curve is generated for each element of interest.
operator. Training ideally should consist of the basic operation
4.2.2 The computer compares the signals arising from the
of the instrument at the time of installation, followed by an
various elements in the sample to the appropriate calibration
in-depth course one or two months later.Advanced courses are
curve. The concentrations of more than 70 elements may be
also offered at several of the important spectroscopy meetings
determined.
that occur throughout the year as well as by independent
4.3 Sensitivities (see 12.3) in a simple aqueous solution are
training institutes. Several independent consultants are avail-
lessthan1µg/gforalloftheseelements,generallylessthan10
able who can provide training, sometimes at the user’s site.
ng/g for most, and may even be below 1 ng/g for some.
4.3.1 Organic liquids may also be used as solvents with
6. Excitation/Radio Frequency Generators
many yielding sensitivities that are within an order of magni-
6.1 Excitation—A specimen is converted into an aerosol
tude of aqueous limits. Some organic solvents may afford
entrained in a stream of argon gas and transported through a
detectionlimitssimilarorevensuperiortothoseobtainedusing
high temperature plasma.The plasma produces excited neutral
aqueous solutions.
atoms and excited ions. The photons emitted when excited
4.3.2 Directsamplingofsolidmaterialshasbeenperformed
atoms or ions return to their ground states or lower energy
successfully by such techniques as spark or laser ablation, by
levelsaremeasuredandcomparedtoemissionsfromreference
electrothermal vaporization and by slurry nebulization.
materials of similar composition. For further details see Prac-
However, these require greater care in the choice of reference
tice E172.
materialsandtheoperationofthesamplingdevices.Therefore,
solid materials are usually dissolved prior to analysis. 6.2 Radio-Frequency Generator:
6.2.1 An RF generator is used to initiate and sustain the
5. Significance and Use
argon plasma. Commercial generators operate at 27.12 or
5.1 This practice describes the essential components of an 40.68 MHz since these frequencies are designated as clear
ICP-AES. The components include excitation/radio-frequency frequencies by U.S. Federal Communications Commission
E1479 − 16
(FCC) regulations. Generators typically are capable of produc- 7.2.2 Some nebulizers, designated as self-aspirating pneu-
ing1.0kWto2.0kWforthe27.12MHzgeneratorand1.0kW matic nebulizers, operating on the Venturi principle, create a
to 2.3 kW for the 40.68 MHz generator. partial vacuum to force liquid up a capillary tube into the
6.2.2 Generators more powerful than 2.5 kW are of limited nebulizer. Precision of operation may be improved if a peri-
practical analytical utility and are not commercially marketed staltic pump controls the solution flow rate.
with ICPspectrometers.The power requirements are related to
7.2.3 Othernebulizersrequireanauxiliarydevice,suchasa
torch geometry and types of samples to be analyzed. Refer to
peristaltic pump, to drive solution to the nebulizer. Generally,
Practice E172 for details. More power (typically 1.5 kW to 2
pump-fed nebulizers are more tolerant of high levels of
kW for a 27.12 MHz generator utilizing a 20-mm outside
dissolved solids and much less affected by suspended solids
diameter torch and 1.2 kW to 1.7 kW for a 40.68 MHz
and viscosity variations.
generator) is required for analyzing samples dissolved in
7.2.4 If fluoride is present in solutions to be analyzed, it is
organicsolventsthanisneededforaqueoussolutions(approxi-
necessary to employ a nebulizer fabricated from HF-resistant
mately 1.0 kW to 1.4 kW). Less power is required for small
materials (see 7.4.1.). It is possible to use the HF-resistant
diameter torches (for example, 650 W to 750 W for a 13-mm
nebulizer for most other types of solutions, but sensitivity and
outside diameter torch).
precision may be degraded.An HF-resistant nebulizer may be
6.3 Load Coil:
more expensive to acquire and repair, and require greater
6.3.1 A coil made from copper (or another metal or alloy operator proficiency and training than other nebulizers.
with similar electrical properties) transmits power from the
7.3 Self-Aspirating or Non-Pump-Fed Nebulizers:
generator to the plasma torch (see 7.6). A typical design
7.3.1 Concentric Glass Nebulizers (CGN):
consists of a two- to six-turn coil of about 1-in. (25-mm)
7.3.1.1 CGNs consist of a fine capillary through which the
diameter, made from ⁄8-in. (3-mm) outside diameter and
⁄16-in. (1.6-mm) inside diameter copper tubing (though larger sample solution flows surrounded by a larger tube drawn to a
fine orifice (concentric) slightly beyond the end of the central
tubing is used with two-turn coils). The tubing is fitted with
ferrules or similar devices to provide a leak-free connection to capillary (see Fig. 2). Minor variations in capillary diameter
andplacementaffectoptimaloperatingpressureforthesample
a coolant, either recirculated by a pump or fed from a
municipal water supply. Modern instruments also utilize air gas flow and change the sample solution uptake rate. Uptake
convection/radiation-cooledsolidloadcoils,completelyavoid- rates of liquid are typically 0.5 mL/min to 3 mL/min.
ing leak risks from liquid cooling.
7.3.1.2 CGNs exhibit somewhat degraded sensitivity and
6.3.2 Especiallyforliquid-cooledloadcoils,thehighpower
precision for solutions that approach saturation or concentra-
conductedbythecoilcanleadtorapidoxidation,surfacemetal
tionsofmorethanafewtenthsofapercentofdissolvedsolids.
vaporization, RF arc-over and even melting if the coil is not
This problem can be greatly reduced by using an inner argon
cooled continuously.
stream that has been bubbled through water in order to
6.3.3 Asafety interlock must be included to turn off the RF
humidify the sample gas argon. Furthermore, since suspended
generator in case of loss of cooling.
solids may clog the tip, it is desirable to include a piece of
capillary tubing of even smaller diameter in the sample
6.4 Impedance Matching:
solution uptake line. This action will isolate a potential
6.4.1 To optimize power transfer from the generator to the
clogging problem prior to clogging at the nebulizer tip.
inducedplasma,theoutputimpedanceofthegeneratormustbe
7.3.2 Micro-Concentric Nebulizer (MCN):
matched to the input impedance of the load coil. Some
instruments include an operator-adjustable capacitor for im-
7.3.2.1 To some extent, the MCN mimics the concept and
pedance matching.
function of the CGN but the MCN employs a thinner-walled
6.4.2 Alternately,RFfrequencymaybeautomaticallytuned poly-ether-imide capillary and TFE-fluorocarbon (or other
or varied in free-running fashion against a fixed capacitor-
polymer)outerbodytominimizeoreliminateundesirablelarge
inductor network. However, most modern instruments incor-
porate either an automatic impedance matching network or a
self-adjusting ‘free running’RF generator to simplify ignition,
to reduce incidence of plasma extinction when introducing
sample solutions, and to optimize power transfer.
7. Sample Introduction
7.1 The sample introduction system of an ICP instrument
consists of a nebulizer, a spray chamber, and a torch.
7.2 Nebulizers:
7.2.1 Samples generally are presented to the instrument as
aqueous or organic solutions. A nebulizer is employed to
convertthesolutiontoanaerosolsuitablefortransportintothe
plasma where vaporization, atomization, excitation, and emis-
sion occur. FIG. 2 Concentric Glass Nebulizer (CGN)
E1479 − 16
4,5
drop formation and facilitate HF tolerance (see Fig. 3 ). A
true aerosol, as opposed to a mist, is produced consisting of
only the desired smallest size droplets. Liquid uptake rates to
produce similar sensitivity to CGNs are sharply reduced with
the MCN. The MCN utilizes typical uptake rates of <0.1
mL/min and is HF tolerant. Unusually small sample size, low
uptake rates, fast washout times, and very low drain rates
characterize this nebulizer. The low uptake rate is particularly
beneficial for extending limited sample volumes so that the
long nebulization times encountered with sequential spectrom-
eters performing multielement analysis may be successfully
accomplished.
7.3.2.2 The initial purchase cost is higher for the MCN than
for the CGN but the cost may be offset by a substantial
FIG. 4 Cross-Flow Nebulizer
reduction in recurring hazardous waste disposal cost (for
example, heavy metal salts, mineral acids, etc.). This disposal
costreductionisbecauseoftheminimalwastevolumeinherent
with low sample uptake rates and significantly reduced drain
rates. In addition, micro-autosamplers that are compatible with
the MCN are available for the optimum handling of small
sample volumes.
7.3.3 Cross-Flow Nebulizer (CFN)—Consists of two capil-
laries held perpendicularly and with exit tips close together, as
shown in Fig. 4. This nebulizer is preadjusted by the manu-
FIG. 5 Grid Nebulizer
facturer and is known as a fixed cross-flow nebulizer. It
requires little maintenance and is very durable. Problems with
high levels of dissolved and suspended solids are similar to or
less than those of the concentric glass nebulizer. Currently, for
andmountedbetweenthefirstscreenandthespraychamber,is
mostanalyticalapplications,theCFNistypicallyoperatedasa
usually incorporated into the design to improve uniformity of
pump-fed nubulizer.
droplet size and transport. A schematic diagram of a grid
nebulizer is shown in Fig. 5. The grid nebulizer may be
7.4 Pump-Fed Pneumatic Nebulizers:
employed to analyze fluoride-containing solutions, but an
7.4.1 Grid Nebulizer—constructed from a fine-mesh screen
HF-resistant spray chamber and torch must also be used.
of acid and solvent resistant material, such as platinum,
7.4.2 Babington, Modified Babington or V-Groove Nebu-
mounted vertically in an inert housing. Sample solution is
lizer:
pumped over the surface of the mesh. A high-velocity gas
7.4.2.1 These nebulizers operate by passing an argon gas
stream is directed through the openings in the screen, shearing
flow through a falling film of flowing analyte solution. The
the liquid from the wetted surface.Afine mist is produced and
falling film is typically guided by a shallow groove or channel
transported to the plasma.Asecond screen, parallel to the first
to a pressurized argon orifice. Film thickness varies with
channel depth, surface texture, cleanliness, and wettability
(hydrophilicity), as well as liquid viscosity, surface tension,
Courtesy of CETAC Technologies, a division of Transgenomic Inc., 5600 S.
42nd St., Omaha, NE. andsampledeliverypumprate.Thenebulizerdoesnotaspirate
naturallyandmustbepumpedtofillthegrooveorchannelwith
sample liquid.
7.4.2.2 This nebulizer can tolerate extremely high levels of
dissolvedandsuspendedsolids,butsomeearlyversionsofthis
devicehavedevelopedareputationfornotbeingassensitiveor
precise as a pneumatic or grid-type nebulizer. However, more
recent versions easily perform as well as concentric or grid
nebulizers. Most Babington nebulizers are HF-resistant. An
example of a common arrangement is shown in Fig. 6.
Alternate configurations may be used.
7.5 Spray Chamber:
Courtesy of Leeman Labs, Inc., 110 Lowell Rd., Hudson, NH 03051.
This nebulizer is sometimes misnamed a cross-flow nebulizer. It is most
properly named a Babington or modified Babington nebulizer after the original and
4, 5
FIG. 3 Micro-Concentric Nebulizer (MCN) pertinent patent holder.
E1479 − 16
FIG. 6 Babington-Type Nebulizer
7.6 Plasma Torch—The argon gas that forms the plasma is
directed through the load coil by means of a plasma torch.
7.6.1 The classic ICP torch is constructed of three concen-
tric quartz tubes sealed together and is known as a ‘one-piece’
or ‘fixed’ torch (see Fig. 8 ). These torches produce good
plasma stability and are easy to use. However, they are, in
general,notHF-resistantand,ifdamaged,theentiretorchmust
be replaced.
7.6.2 Thedemountabletorch(seeFig.9 )isincommonuse
particularly since the individual tubes can be replaced without
replacing the entire assembly.
FIG. 7 Spray Chamber
7.6.3 Alternate construction materials (typically ceramics)
maybeemployedforanalyzingsolutionscontainingsignificant
7.5.1 Thespraychamberprovidesanaerosoldroplet-sorting
quantities of fluoride ion that attack quartz.
function to ensure that only the smaller droplets (typically less
7.6.4 In place of quartz, fixed or demountable torches are
than 10 µm) reach the plasma. This ensures that the plasma is
commonly made of an HF-resistant ceramic. For demountable
not significantly overloaded with solvent. The larger droplets
torches, all tubes, or often only the central or injector tube, are
are condensed and drained away from the spray chamber. If a
made from a corrosion-resistant ceramic.
peristaltic pump is used to remove the waste liquid from the
7.6.5 If fluoride-containing solutions are to be analyzed
spray chamber during nebulization, the pump tubing for the
routinely, the design and performance of the prospective
drain should be of a higher flow rating than that used for the
manufacturer’s HF-resistant torch should be evaluated.
intake.
7.5.2 A positive pressure must be maintained in the spray 7.6.6 There may be significant variations concerning instal-
chamber to prevent air ingress and deliver the sample aerosol lation and operation, and in costs of repair and maintenance.
to the torch. Therefore, it is vital to ensure that all connections
7.6.7 Alternately,itmaybepossibletobuildanHF-resistant
between the spray chamber and the ICP torch are leak-proof
system or acquire one from a manufacturer different than the
and that the drain plug is secure. If a peristaltic pump under
manufacturer of the spectrometer.
computer control is incorporated, automatic start-up and shut-
7.6.8 Before purchasing a third-party torch system, a dem-
down can be achieved without depleting sample solution.
onstration of both repeated plasma ignition reliability and
7.5.3 A common ICP spray chamber is a double-pass-type
fabricated of glass (see Fig. 7). If fluoride is present in
solutions to be analyzed, it is necessary to employ a spray
Courtesy of Spectro Analytical Instruments GmbH, Boschtr, 10 47533 Kieve,
chamberconstructedfromHF-resistantmaterials.Itispossible
Germany.
to use the HF-resistant spray chamber for other types of
Courtesy of Texas Scientific Products (TSP), 11941 Hilltop Rd., Suite 15,
solutions. Argyle, TX.
E1479 − 16
however, may also improve performance with aqueous
samples. Third, an inner (sample or nebulizer) flow (typically
0.4 L/min to 1 L/min) passes through the sample introduction
device and transports the analyte through the injector tip into
the plasma. The manufacturer should provide data on optimal
ranges for each of the gas flows since torch geometry strongly
influences optimal rates.
7.7.2 Anargonsheathattachment,adeviceforchangingthe
flow rate of the intermediate flow during the analysis by
introducinganadditionalargonflowundercomputercontrol,is
available.Thisadditionalflowaffectstheobservationzonethat
is viewed by the spectrometer and, consequently, for example,
enhanced detection limits for the alkali metals and alkaline
earths may be realized. Furthermore, the argon sheath attach-
ment may also prevent salt encrustation in the inner tube with
elevated salt concentration samples.
7.7.3 The inner gas flow rate is the most critical because it
affectstheinjectionefficiencyandresidencetimeofthesample
in the plasma and, especially for a pneumatic nebulizer (see
7.3),influencestransportefficiencyofbothanalyteandsolvent
species. Both sensitivity and position of the maximum signal-
to-noise ratio within the plasma are dependent on sample gas
pressure and flow rate.
7.7.4 A conventional regulator and rotameter provide ad-
FIG. 8 Typical One-Piece Quartz Torch
equate stability in most cases, but a precision pressure
controller, a mass flow controller (MFC) or a volume flow
controller (VFC) may be required in certain applications.
Accordingly, most modern instruments employ mass or vol-
umeflowcontrollersatleastforthecentralornebulizerflowor
for all plasma gas flows. The intermediate flow affects the
vertical location of the plasma relative to the torch and load
coil. Gross variations will affect accuracy and precision. If
available, the user should compare results with and without
MFCs to determine their impact on performance.
7.7.5 In all but the most robust (all ceramic) torches, loss of
outer gas flow through the torch will lead to rapid melting. A
safety interlock must be included in the instrument design to
turn off power to the RF generator in case of loss of argon
FIG. 9 Demountable Torch
pressure.
7.8 Alternate Sample Introduction Devices:
analytical performance with the fluoride medium in the in-
7.8.1 Ultrasonic Nebulizer (USN):
tended model spectrometer is recommended unless a satisfac-
7.8.1.1 AUSNwithdesolvationisthemostgenerallyuseful
tory guarantee of analytical performance and ignition reliabil-
alternatesamplingdevice.Inthisdevice,thesamplesolutionis
ity is obtained.
pumped over the face of a quartz-coated crystalline transducer
7.7 Gas Flow:
driven by a low-power RF generator (see Fig. 10). The
7.7.1 There are usually three gas flows through the torch.
apparatus is about ten times as efficient as the self-aspirating
The first is the outer (coolant or plasma) gas flow which is
and pumped pneumatic nebulizers described in 7.3 and 7.4,
directed tangentially to the internal surface of the largest
respectively, and is useful for situations requiring very high
diameter portion of the torch (typically 12 L/min to 20 L/min
sensitivity. Sensitivity is about ten times better with a USN
although some torches are designed to operate on much lower
than with self-aspirating and pumped pneumatic nebulizers.
flow rates). Second, an intermediate (auxiliary) gas flow
However, the USN device is more expensive and may require
(typically0.5L/minto1L/min)isdirectedbetweenthecentral
more maintenance than the pneumatic types.
tube through which the sample aerosol is introduced and the
7.8.1.2 Operation of the USN without desolvation is gener-
outer tube to reduce carbon formation on the injector tip when
ally not practical because the large amount of aerosol reaching
organic samples are being analyzed and to prevent the plasma
from collapsing onto the injector tip. That intermediate flow, the plasma creates an excessive solvent load which reduces
E1479 − 16
7.8.2.3 Take care to match samples and reference materials
andtoensurethatanalytesareconvertedtotheproperchemical
form for quantitative conversion to the desired hydrides.
Commercial equipment is available or the literature may be
consulted to design and build a suitable apparatus. While
hydride generation was performed in a transient manner in
older atomic absorption systems, often the data acquisition
systems of commercially available ICP-AES systems are more
conducive to continuous generation.
7.8.3 Electrothermal Vaporization (ETV):
7.8.3.1 ETVmaybeemployedwheresamplesizeislimited.
As with hydride generation, the transient nature of ETV is not
well suited to conventional ICP-AES data acquisition systems
and may not work at all with many such systems.An efficient
application of ETV usually requires a (fully) simultaneous
ICP-AES instrument with a sufficiently high data rate (typi-
cally 10 Hz) for the ETV-generated transient analyte signals of
interest. Accordingly, ETV is particularly unsuited to sequen-
tial spectrometer systems because relatively slow wavelength
change between sequentially determined elements precludes
anypossibilityoftransientmultielementETVanalysisonthese
systems.Becauseofextendeddryandashcycles,ETVsystems
have substantially slower cycling times in terms of sample
FIG. 10 Ultrasonic Nebulizer
throughput rate.
7.8.3.2 AutosamplersforETVcanbefarmorecomplexand
expensive and might not be as readily available as they are for
pneumatic nebulizers. Still, commercial systems allowing au-
excitation efficiency and negates all potential sensitivity ad-
tomatic ETV processing of up to 50 samples are available.
vantage. The aerosol, therefore, is passed through a heated
7.8.3.3 ETV precision is typically worse than that of gas
zone followed by a condenser to limit solvent loading of the
nebulization and, therefore, requires a greater number of
plasma.
replicatedeterminations.Also,theinterferenceeffectsaremore
7.8.1.3 Solutions with relatively high concentrations of
intricateandextensive.TheprospectiveuserofETVshouldtry
dissolved solids or uncomplexed fluoride ion may not be
the desired analysis at the manufacturer’s application labora-
suitable for ultrasonic nebulization.
tory before purchasing an instrument.
7.8.1.4 Ultrasonic nebulizers may be slightly less stable
7.8.4 Sampling Solid Materials—Approaches to direct
than pneumatic nebulizers although USN performances of
analysis of solid materials include insertion of a graphite rod
between 0.5 % RSD and 1% RSD are typical with recent
containing the specimen into the plasma, arc or spark ablation,
versions. The user should ensure that short-term precision
laserablation,orslurrynebulization.Sinceconsiderableskillis
(≤1% RSD for raw, uncorrected, unratioed signals) and
required, these techniques cannot be recommended for the
long-term drift rates are adequate for all anticipated applica-
beginner or casual user. Commercial devices are available, but
tions.
the prospective user should evaluate them critically before
7.8.2 Hydride Generation:
purchase to ensure that the required sensitivity, precision, and
7.8.2.1 Hydride generation is useful for elements which
accuracy may be attained in the sample medium of interest.
may be converted to volatile hydrides. This technique affords
Considerablecareisrequiredinselectingappropriatereference
improved sensitivity and avoids interferences arising from
materials for accurate calibration.
spectral overlap with non-volatile concomitants.
7.9 Autosamplers—Forsituationsinwhichlargenumbersof
7.8.2.2 Interference occurs instead in the form of chemical
similar samples are to be analyzed, an automated sample
inhibition of the hydride reaction. Concentrated transition
introduction system may be desirable. Such a device may be
metal or precious metal media or selected dissolved oxidants,
purchased from the manufacturer of the spectrometer or
or a combination thereof, produce the worst interferences.
acquired from another supplier.
Combinations of metal and certain oxidants (notably, HNO
and its residues) can be particularly troublesome because of 7.9.1 Two types of autosamplers are generally available.
metal-induced catalytic effects which amplify the chemical Thesimplerandlesscostlyisasequentialdevicethatprocesses
inhibition. Optimization of reagent (reductant) concentration, samples in the sequence in which they are loaded into a rack
generallyloweringtotherangebetween0.5%and1%NaBH prior to starting analysis. More sophisticated devices allow
or less, can minimize or eliminate catalytic inhibition and random access. This capability usually is coupled with an
frequently reduce the magnitude of interference to a range appropriate computer hardware/software system, or preferably
where standard addition or matrix matching become at least directly integrated into the ICP-AES instrument software to
usable calibration schemes. allowrecalibrationifresultsforqualitycontrolcheckmaterials
E1479 − 16
are not within a specified range, or to repeat analyses if eralthousandtoover250,000individualpixels.Suchadvanced
duplicatesdonotagreewithinacceptablelimitsofprecision.If array detectors can theoretically be fitted with an image
the user wishes to acquire an autosampler from a source other intensifier plate, but are typically operated at unity gain to
than the instrument manufacturer, the compatibility and soft- control costs. Echelle-based spectrometers can either allow
ware integration capability must be verified by consultation simultaneous ‘full’ spectrum capture or – in the form of an
with the manufacturer of the spectrometer, and preferably by ‘EchelleMonochromator’–thesimultaneouscaptureofasmall
actual product demonstration. wavelength region around the analytical emission line of
interest, typically sufficient for simultaneous background cor-
rection. Also, Echelle-based ‘full spectrum’ systems are com-
8. Spectrometers
mercially available that cover the relevant emission spectrum
8.1 ICPspectrometersmaybeclassifiedassequentialtypes,
in, for example, two integrations, each consisting of about half
simultaneous types, a combination of the two called
of the full spectral range.
simultaneous/sequentialsystems,eitheremployinga‘classical’
8.1.4.1 Spectrometers based on the Paschen-Runge Mount,
photomultiplier tube (PMT) as detector, or a solid state
with a single or several concave diffraction gratings and a
detector. Most of the commercial instruments available cur-
numberoflinearsolidstatedetectorarraysarrangedaroundthe
rently utilize semiconductor solid state detectors, mainly in
Rowland Circle to detect the wavelength dispersed radiation
conjunction with simultaneous or simultaneous/sequential
within a single diffraction order (usually the 1st only) reach a
spectrometers, where the latter, for example, allows for the
high and constant spectral resolution over large wavelength
simultaneous detection of a certain wavelength interval around
ranges. The lack of transmission optical components as, for
the analyte emission line(s) or even a larger spectral region.
example,aprismforordersorting,allowsfordeepUVspectral
8.1.1 Sequential Spectrometers with PMT(s)—Perform de-
performance,downto130nminsomecommercialintruments.
terminations by means of a monochromator and one or more
Like Echelle systems, Paschen-Runge systems that capture the
photomultipliers. Commercially available instruments may
fullspectralrangeinseveral(typicallytwo)individualintegra-
select the wavelength to be monitored either by rotating the
tions also exist. Finally, solid state detector systems based on a
grating of the monochromator or moving the photomultiplier
Czerny-Turner Monochromator permitting the capture of the
tube. Some spectrometers contain more than one monochro-
analyte emission and a certain wavelength interval around it
mator or detector to improve rate of data acquisition or to
simultaneously exist commercially.
optimize performance in each of several spectral regions, or
8.1.4.2 Except for being used as a simultaneous
both. In addition, a second monochromator may monitor a
spectrometer, solid state detectors have some distinct differ-
reference wavelength, thus permitting real-time internal stan-
ences to other spectrometers.
dardization for improved precision.
8.1.4.3 For Echelle-based systems, the lack of detector gain
8.1.2 Simultaneous Spectrometers with PMT(s)—
above unity and the compact echelle format, which is charac-
Conventional simultaneous spectrometers usually employ one
terized by the unusually short slit height required for prismatic
or more separate exit slits and photomultiplier tubes for each
order sorting collectively have an adverse effect on system
element of interest. A typical polychromator consists of an
sensitivity unless offsetting factors are introduced.
entrance slit, a diffraction grating, and exit slits located on the
8.1.4.4 Successful offsetting (compensating) factors include
focal curve with a photomultiplier tube behind each exit slit.
various combinations of increased integration time (exposure
Alternatively, the exit slits and photomultiplier tubes may be
time), detector cooling, improved spectrometer f/number (nu-
replacedbyasolidstatedetector(see9.3).Somespectrometers
merical aperture), and axial viewing of a horizontally oriented
have an auxiliary monochromator to allow determination of at
plasma torch.
least one additional element not detected by the array of
8.1.4.5 Similarly for the other solid state detector spectrom-
photomultipliers mounted on the focal curve.
eterdesignsdescribedandcommerciallyavailable,anadaption
8.1.3 Combined Spectrometers with PMT(s)—Some photo-
of spectrometer and detector parameters, for example, de-
multiplier tube-based instruments include each type of spec-
magnification of the diffraction plane image onto the light-
trometerdescribedin8.1.1and8.1.2.Thisdesigncombinesthe
sensitivedetectorpartcanoffsettheresultsfromgeometricand
advantages of the superior speed, excellent precision, and
detector gain differences between PMTs and solid state detec-
simultaneous multielement analysis attainable with a simulta-
tors.
neous instrument and the flexibility to measure the emission at
anysuitableultravioletorvisiblewavelengthusingasequential 8.1.4.6 In at least one case, a combination of the above
parameters consistently yielded routine sensitivity for an ad-
scanning spectrometer.
vanced array detector equaling that of photomultiplier tubes.
8.1.4 Solid State Detector Spectrometers—Several, usually
This is also proven by the fact that the majority of ICP-AES
simultaneous, spectrometer designs can be combined with
instruments sold commercially currently utilize solid state
solidstatedetectorsadvantageouslyandareavailablecommer-
detection, for the advantages described below.
cially. Echelle spectrometers are available to provide high
resolution in a compact x-y wavelength presentation format. 8.1.4.7 An advantage of advanced array detectors is sub-
The compact format allows imaging of the spectrum onto one stantially larger numbers of simultaneously determined ele-
or more silicon wafer array detectors including photodiode ments.Inmanycasestwoormoreanalyticalspectrallinesmay
arrays (PDA), charge coupled device (CCD) arrays and charge besimultaneouslymonitored.Otheradvantagesinclude:simul-
injection device (CID) arrays containing anywhere from sev- taneousbackgroundcorrectionadjacenttoeveryspectrallineis
E1479 − 16
easily performed and offers potentially greater accuracy; alter- 8.2.2.3 The sequential spectrometer may be designed to
nate line selection provides more flexibility to minimize or move in turn to each approximate wavelength and perform a
avoid spectral interference, or to increase the overall system peak search before taking the measurement.
concentration dynamic range for a given element with both 8.2.3 For all designs, it is necessary to provide internal
strongandweaklinesareavailableformanyelements,orboth;
temperature control, or to design and construct the spectrom-
availability of chemometric enhancement of signal to noise eter so that stability may be achieved without temperature
ratio using multiple lines of each element, including (full-
control.
spectrum) modelling approaches for spectral interference cor-
8.2.4 Since temperature and humidity changes may also
rection. Finally, the availability of a complete spectrum with
affectthesampleintroductionsystem,detectors,andelectronic
each measurement opens the possibility for retrospective
readout, some manufacturing specifications may require that
analysis, for example, detection of elements present in the
care be used in selecting a location for the spectrometer which
sample not included in the original analytical program.
experiences minimal variation in temperature and relative
8.1.4.8 Short wavelength sensitivity inherently varies from humidity. It is the responsibility of the user to provide a
one device type to the next and for many years was a severe controlled environment as specified by the manufacturer.
limitation. Modern silicon wafer technology can improve poor
8.3 Optical Path:
UV photosensitivity limits by either elimination of the surface
8.3.1 Since oxygen exhibits increasing absorbance with
oxide dead layer during manufacture or by phosphor coatings.
decreasing wavelength below 200 nm, the performance of an
By either means, several systems are available with spectral
air path instrument degrades below that wavelength and
response extending easily to wavelengths less than 167 nm,
generally is not useful below approximately 190 nm.
down to 130 nm.
8.3.1.1 Purging the optical path with nitrogen or argon, or
8.1.4.9 Considerationsinselectinganadvancedarraydetec-
another gas with low absorption in the ultraviolet region may
torsystemshouldincludespectralresolution,sensitivityforall
extend the spectral region to wavelengths less than 167 nm.
elementsofinterest,particularlyelementsthatgiverisetoshort
Use of nitrogen as the purge gas is, in general, less expensive
wavelength emissions, the number of available detector pixels,
to maintain than vacuum path systems. Purge rates required to
and the number of elements that can be simultaneously
achieveagivenperformancelevel(below200nm)varywidely
determinedinthesamplemediumofinterest.Often,thelargest
according to the manufacturing design of the spectrometer,
number of pixels does not guarantee the best results. Resolu-
volume to be purged, and the extent of leaks in the spectrom-
tion sensitivity must be considered in the sample medium of
eter housing. Before purchase, it is advisable to check the
interest.
purge gas rate (L/min) required to achieve specified detection
8.2 Spectrometer Environment:
limits below 200 nm.
8.2.1 Temperature fluctuations affect instrument stability. 8.3.1.2 Alternatively, the spectrometer optical compartment
Some manufacturers provide systems for maintaining a con- may be purged with nitrogen or argon, sealed and maintained
stant internal temperature within the optical compartment and at a constant pressure. The nitrogen or argon is continuously
sample introduction area provided that changes in the outside filtered over reactive catalysts to scrub out oxygen and water.
temperature are controlled within a specified range and rate of With modification to certain optical components in the
change. Other manufacturers design their spectrometers to be spectrometer, wavelengths can be extended to 120 nm.
stableoveraspecifiedtemperaturerangewithoutattemptingto 8.3.1.3 Vacuum path instruments are more expensive and
control the spectrometer’s internal temperature.
require additional maintenance.
8.2.2 Changes in the refractive index of the atmosphere
8.3.1.4 For purged, closed purged and vacuum systems,
affecttheopticalpath.Manufacturersprovidevariousmeansto isolation of the optics from the laboratory environment will
compensate for these changes, including use of evacuated
lengthen the useful lifetime of mirrors, gratings, and refractor
(vacuum), sealed gas-filled, purged, or precise, pressure- plates (if present), especially if the environment contains
controlled, gas-purged spectrometers, or use of optical com-
significant concentrations of acid fumes.
pensation as follows:
8.3.1.5 If purging or vacuum are operated continuously,
8.2.2.1 Simultaneous instruments can be equipped with there is no effect on data acquisition rate once equilibrium has
movable entrance slits or a rotating refractor plate behind the
been achieved in the spectrometer. Alternatively, with proper
slit to shift the image of the entrance slit onto the exit slits. If designandconstruction,avacuumspectrometermayincludea
equipped with a suitable ‘full spectrum’ detector (normally a
feedback system to turn the vacuum pump on when an upper
solid state detector(s) array), simultaneous spectrometers may limit of about 10 Torr is exceeded and to stop the pump when
utilize a full-spectrum pattern matching algorithm to compen-
aspecifiedlowerlimitisachieved.Consideringthetotalcostof
sate for wavelength drift, using, for example, known emission operating a spectrometer for several years, the difference
line positions from a known reference sample or plasma
among vacuum, purge, and air-path spectrometers should be
background emissions (for example, Ar lines). considered by assessing the costs of the required purge gas, of
8.2.2.2 Sequential spectrometers may be designed to locate possible consumables or replacement parts, and possibly re-
quired periodic maintenance.
an intense reference line before each measurement and then,
under computer control, make measurements at a predeter- 8.3.2 While most commercially available instruments are
mined wavelength distance from that reference line for each designed to collect radiation from the plasma directly, an
spectral line to be measured, or acceptable alternative is the use of a fiber optic cable to
E1479 − 16
transmit radiation to the entrance slit of the spectrometer for considered for polychromator-based systems to reduce overlap
wavelengths above 200 nm assuming the fiber optic wave- from higher order lines.
lengthcutoffdoesnotnegatetheuseofimportantanalytelines.
8.4.2.5 Solid state array detector based systems of any type
Also, the cutoff wavelength may increase with age because of
are especially well suited for a multitude of analytical tasks.
photodegradation. Photodegradation may also cause deteriora- Weak-line (high concentration) analytical channels of major
tion of the fiber optic itself requiring periodic replacement of
elements are often included to assess major element concen-
the cable. It also may be necessary to clean the fiber optic tration and generate dual- or multiple-wavelength spectral
periodically in accordance with the manufacturer’s recom-
interference correction for those trace analyte channels which
mended procedure. are partially overlapped by interfering lines of the major
elements in question.
8.4 Optical Systems:
8.4.3 To reduce cost, some sequential instruments are
8.4.1 Optical Dispersion—The dispersing element in com-
equipped with short optical paths or gratings with low groove
mercially available ICP spectrometers is commonly a diffrac-
density, or both. In contrast, other sequential instruments with
tion grating, though some manufacturers use echelle gratings.
higher groove density and focal length may have better
For a given optical path, higher groove-grating densities or
resolution than echelle spectrometers. Take care, however, to
higher spectral orders, or both, provide better resolution but
ensure that resolution is adequate for all materials likely to be
cover a narrower wavelength interval than gratings with lower
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E1479 − 99 (Reapproved 2011) E1479 − 16
Standard Practice for
Describing and Specifying Inductively-Coupled Inductively
Coupled Plasma Atomic Emission Spectrometers
This standard is issued under the fixed designation E1479; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice describes the components of an inductively-coupled inductively coupled plasma atomic emission spectrometer
(ICP-AES) that are basic to its operation and to the quality of its performance. This practice identifies critical factors affecting
accuracy, precision, and sensitivity. It is not the intent of this practice to specify component tolerances or performance criteria,
since these are unique for each instrument. A prospective user should consult with the vendormanufacturer before placing an order,
to design a testing protocol to demonstrate that demonstrates the instrument meets all anticipated needs.
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. Specific safety hazard statements are given in Section 13.
2. Referenced Documents
2.1 ASTM Standards:
E135 Terminology Relating to Analytical Chemistry for Metals, Ores, and Related Materials
E158 Practice for Fundamental Calculations to Convert Intensities into Concentrations in Optical Emission Spectrochemical
Analysis (Withdrawn 2004)
E172 Practice for Describing and Specifying the Excitation Source in Emission Spectrochemical Analysis (Withdrawn 2001)
E416 Practice for Planning and Safe Operation of a Spectrochemical Laboratory (Withdrawn 2005)
E520 Practice for Describing Photomultiplier Detectors in Emission and Absorption Spectrometry
3. Terminology
3.1 Definitions—For terminology relating to emission spectrometry, refer to Terminology E135.
4. Summary of Practice
4.1 An ICP-AES is an instrument used to determine elemental composition. It typically is comprised of several assemblies
including a radio-frequency (RF) generator, an impedance matching network (where required), an induction coil, a plasma torch,
a plasma ignitor system, a sample introduction system, a light radiant energy gathering optic, an entrance slit and dispersing
element to sample and isolate wavelengths of light emitted from the plasma, one or more devices for converting the emitted light
into an electrical current or voltage, one or more analog preamplifiers, one or more analog-to-digital converter(s), and a dedicated
computer with printer (see Fig. 1 ).
4.1.1 The sample is introduced into a high-temperature (>6000 K) plasma that is formed from the inductive energy transfer to
and subsequent ionization of the gas stream contained in the torch. The torch is inserted through metal tubing formed into a helix,
mounted centrally in a metal structure, which is called the load coil. Energy is applied to the load coil by means of an RF generator.
This practice is under the jurisdiction of ASTM Committee E01 on Analytical Chemistry for Metals, Ores, and Related Materials and is the direct responsibility of
Subcommittee E01.20 on Fundamental Practices.
Current edition approved Nov. 15, 2011Nov. 1, 2016. Published June 2012December 2016. Originally approved in 1992. Last previous edition approved in 20052011 as
E1479 – 99 (2005).(2011). DOI: 10.1520/E1479-99R11.10.1520/E1479-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Courtesy of PerkinElmer, Inc., 761 Main Ave., Norwalk, CT 06859.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1479 − 16
FIG. 1 Components of Inductively Coupled PlasmaICP-AES
4.1.2 The term inductively-coupled inductively coupled refers to the fact that the physical phenomenon of induction creates a
plasma by transferring energy from the load coil to the gas stream that has been momentarily preionized by a high voltage ignitor
electrodespark that functions only during plasma ignition.
4.2 When material passes through the plasma, it is vaporized, atomized, and many elements are almost completely ionized.
partly ionized. The produced atoms and ions are excited into an energetically higher state. Free atoms and ions are excited by
collision from their ground states. When the states mainly by collision with the major plasma constituents. The excited atoms or
ions subsequently decay to a lower energy state, theystate and emit photons, some of which pass through the entrance slit of a
spectrometer. Each element emits a unique set of emission lines. Photons of a desired wavelength may be selected from the
ultraviolet and visible spectra by means of a dispersing element.
4.2.1 Instruments may determine elements either simultaneously or sequentially. The output of the detector generally is directed
to a preamplifier, an analog-to-digital converter, and a computer which measures and stores a value proportional to the electrical
current or voltage generated by the detector(s). Using blank and known calibration solutions, a calibration curve is generated for
each element of interest.
4.2.2 The computer compares the signals arising from the various elements in the sample to the appropriate calibration curve.
The concentrations of more than 70 elements may be determined.
4.3 Sensitivities (see 12.3) in a simple aqueous solution are less than one part per million (ppm) 1 μg/g for all of these elements,
generally less than 10 parts per billion (ppb) ng/g for most, and may even be below 1 ppbng/g for some.
4.3.1 Organic liquids may also be used as solvents with many yielding sensitivities that are within an order of magnitude of
aqueous limits for many common organic solvents. limits. Some organic solvents may afford detection limits similar or even
superior to those obtained using aqueous solutions.
4.3.2 Direct sampling of solid materials has been performed successfully by such techniques as spark or laser ablation and
ablation, by electrothermal vaporization and by slurry nebulization. However, these require greater care in the choice of reference
materials and the operation of the sampling devices. Solid materials, therefore,Therefore, solid materials are usually dissolved prior
to analysis.
5. Significance and Use
5.1 This practice describes the essential components of an inductively-coupled plasma atomic emission spectrometer
(ICP-AES). ICP-AES. The components include excitation/radio-frequency generators, sample introduction systems, spectrometers,
detectors, and signal processing and displays. This description allows the user or potential user to gain a cursory understanding
of an ICP-AES system. This practice also provides a means for comparing and evaluating various systems, as well as understanding
the capabilities and limitations of each instrument.
E1479 − 16
5.2 Training—The vendormanufacturer should provide training in safety, basic theory of ICP spectrochemical ICP-AES
analysis, operations of hardware and software, and routine maintenance for at least one operator. Training ideally should consist
of the basic operation of the instrument at the time of installation, followed by an in-depth course one or two months later.
Advanced courses are also offered at several of the important spectroscopy meetings that occur throughout the year as well as by
independent training institutes. Furthermore, several Several independent consultants are available who can provide training, in
most cases sometimes at the user’s site.
6. Excitation/Radio Frequency Generators
6.1 Excitation—A specimen is converted into an aerosol entrained in a stream of argon gas and transported through a high
temperature plasma. The plasma produces excited neutral atoms and excited ions. The photons emitted when excited atoms or ions
return to their ground states or lower energy levels are measured and compared to emissions from reference materials of similar
composition. For further details see Practice E172.
6.2 Radio-Frequency Generator:
6.2.1 An RF generator is used to initiate and sustain the argon plasma. Commercial generators operate at 27.12 andor 40.68
MHz since these frequencies are designated as clear frequencies by U.S. Federal Communications CommitteeCommission (FCC)
regulations. Generators typically are capable of producing 1.0 kW to 2.0 kW for the 27.12 MHz generator and 1.0 kW to 2.3 kW
for the 40.68 MHz system.generator.
6.2.2 Generators more powerful than 2.5 kW are of limited practical analytical utility and are not commercially marketed with
ICP spectrometers. The power requirements are related to torch geometry and types of samples to be analyzed. Refer to Practice
E172 for details. More power (typically 1.5 kW to 2 kW for a 27.12 MHz systemgenerator utilizing a 20-mm outside diameter
torch and 1.2 kW to 1.7 kW for a 40.68 MHz generator) is required for analyzing samples dissolved in organic solvents than is
needed for aqueous solutions (approximately 1.0 kW to 1.4 kW). Less power is required for small diameter torches (for example,
650 W to 750 W for a 13-mm outside diameter torch).
6.3 Load Coil:
6.3.1 A coil made from copper (or another metal or an alloy with similar electrical properties) is used to transmit transmits
power from the generator to the plasma torch (see 7.6). A typical design consists of a two- to six-turn coil of about 1-in. (25-mm)
1 1
diameter, made from ⁄8-in. (3-mm) outside diameter and ⁄16-in. (1.6-mm) inside diameter copper tubing (though larger tubing is
used with two-turn coils). The tubing is fitted with ferrules or similar devices to provide a leak-free connection to a coolant, either
recirculated by a pump or fed from a municipal water supply. Argon gas blown through the coil has been used to cool other load
coils.Modern instruments also utilize air convection/radiation-cooled solid load coils, completely avoiding leak risks from liquid
cooling.
6.3.2 The Especially for liquid-cooled load coils, the high power conducted by the coil can lead to rapid oxidation, surface metal
vaporization, RF arc-over and even melting if the coil is not cooled continuously.
6.3.3 A safety interlock must be included to turn off the RF generator in case of loss of coolant flow.cooling.
6.4 Impedance Matching:
6.4.1 To optimize power transfer from the generator to the induced plasma, the output impedance of the generator must be
matched to the input impedance of the load coil. Some instruments include an operator-adjustable capacitor for impedance
matching.
6.4.2 Alternately, RF frequency may be automatically tuned or varied in free-running fashion against a fixed capacitor-inductor
network. Most modern instruments, however, incorporate However, most modern instruments incorporate either an automatic
impedance matching network or a self-adjusting ‘free running’ RF generator to simplify ignition, to reduce incidence of plasma
extinction when introducing sample solutions, and to optimize power transfer.
FIG. 2 Concentric Glass Nebulizer (CGN)
E1479 − 16
7. Sample Introduction
7.1 The sample introduction system of an ICP instrument consists of a nebulizer, a spray chamber, and a torch.
7.2 Nebulizers:
7.2.1 Samples generally are presented to the instrument as aqueous or organic solutions. A nebulizer is employed to convert the
solution to an aerosol suitable for transport into the plasma where vaporization, atomization, excitation, and emission occur.
7.2.2 Some nebulizers, designated as self-aspirating pneumatic nebulizers, operating on the Venturi principle, create a partial
vacuum to force liquid up a capillary tube into the nebulizer. Precision of operation may be improved if a peristaltic pump controls
the solution flow rate.
7.2.3 Other nebulizers require an auxiliary device, such as a peristaltic pump, to drive solution to the nebulizer. Generally,
pump-fed nebulizers are more tolerant of high levels of dissolved solids and much less affected by suspended solids and viscosity
variations.
7.2.4 If fluoride is present in solutions to be analyzed, it is necessary to employ a nebulizer fabricated from hydrofluoric acid
(HF)-resistant HF-resistant materials (see 7.4.1.). It is possible to use the HF-resistant nebulizer for most other types of solutions,
but sensitivity and precision may be degraded. An HF-resistant nebulizer may be more expensive to acquire and repair, and require
greater operator proficiency and training than other nebulizers.
7.3 Self-Aspirating or Non-Pump-Fed Nebulizers:
7.3.1 Concentric Glass Nebulizers (CGN):
7.3.1.1 CGNs consist of a fine capillary through which the sample solution flows surrounded by a larger tube drawn to a fine
orifice (concentric) slightly beyond the end of the central capillary (see Fig. 2). Minor variations in capillary diameter and
placement affect optimal operating pressure for the sample gas flow and change the sample solution uptake rate. Uptake rates of
liquid are typically 0.5 mL/min to 3 mL/min.
7.3.1.2 CGNs exhibit somewhat degraded sensitivity and precision for solutions that approach saturation or concentrations of
more thatthan a few tenths of a percent of dissolved solids. This problem can be greatly reduced by using an inner argon stream
that has been bubbled through water in order to humidify the sample gas argon. Furthermore, since suspended solids may clog the
tip, it is desirable to include a piece of capillary tubing of even smaller diameter in the sample solution uptake line. This action
will isolate a potential clogging problem prior to clogging at the nebulizer tip.
7.3.2 Micro-Concentric Nebulizer (MCN):
7.3.2.1 To some extent, the MCN mimics the concept and function of the CGN but the MCN employs a thinner-walled
poly-ether-imide capillary and TFE-fluorocarbon (or other polymer) outer body to minimize or eliminate undesirable large drop
4,5
formation and facilitate HF tolerance (see Fig. 3 ). A true aerosol, as opposed to a mist, is produced consisting of only the desired
smallest size droplets. Liquid uptake rates to produce similar sensitivity to CGNs are sharply reduced with the MCN. The MCN
utilizes typical uptake rates of <0.1 mL/min and is HF tolerant. Unusually small sample size, low uptake rates, fast washout times,
and very low drain rates characterize this nebulizer. The low uptake rate is particularly beneficial for extending limited sample
volumes so that the long nebulization times encountered with sequential spectrometers undertakingperforming multielement
analysis may be successfully accomplished.
7.3.2.2 The initial purchase cost is higher for the MCN than for the CGN but the cost may be offset by a substantial reduction
in recurring hazardous waste disposal cost (for example, heavy metal salts, mineral acids, etc.). This disposal cost reduction is
Courtesy of CETAC Technologies, a division of Transgenomic Inc., 5600 S. 42nd St., Omaha, NE.
4, 5
FIG. 3 Micro-Concentric Nebulizer (MCN)
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FIG. 4 Cross-Flow Nebulizer
FIG. 5 Grid Nebulizer
because of the minimal waste volume inherent with low sample uptake rates and significantly reduced drain rates. In addition,
micro-autosamplers that are compatible with the MCN are available for the optimum handling of small sample volumes.
7.3.3 Cross-Flow Nebulizer (CFN)—Consists of two capillaries held perpendicularly and with exit tips close together, as shown
in Fig. 4. This nebulizer is preadjusted by the manufacturer and is known as a fixed cross-flow nebulizer. It requires little
maintenance and is very durable. Problems with high levels of dissolved and suspended solids are similar to or less than those of
the concentric glass nebulizer. Currently, for most analytical applications, the CFN is typically operated as a pump-fed nubulizer.
7.4 Pump-Fed Pneumatic Nebulizers:
7.4.1 Grid Nebulizer—constructed from a fine-mesh screen of acid and solvent resistant material, such as platinum, mounted
vertically in an inert housing. Sample solution is pumped over the surface of the mesh. A high-velocity gas stream is directed
through the openings in the screen, shearing the liquid from the wetted surface. A fine mist is produced and transported to the
plasma. A second screen, parallel to the first and mounted between the first onescreen and the spray chamber, is usually
incorporated into the design to improve uniformity of droplet size and transport. A schematic diagram of a grid nebulizer is shown
in Fig. 5. The grid nebulizer may be employed to analyze fluoride-containing solutions, but an HF-resistant spray chamber and
torch must also be used.
7.4.2 Babington, Modified Babington or V-Groove Nebulizer:
7.4.2.1 These nebulizers operate by passing an argon gas flow through a falling film of flowing analyte solution. The falling
film is typically guided by a shallow groove or channel to a pressurized argon orifice. Film thickness varies with channel depth,
surface texture, cleanliness, and wetabilitywettability (hydrophilicity), as well as liquid viscosity, surface tension, and sample
delivery pump rate. The nebulizer does not aspirate naturally and must be pumped to fill the groove or channel with sample liquid.
7.4.2.2 This nebulizer can tolerate extremely high levels of dissolved and suspended solids, but some early versions of this
device have developed a reputation for not being as sensitive or precise as a pneumatic or grid-type nebulizer. However, more
recent versions easily perform as well as concentric or grid nebulizers. Most Babington nebulizers are HF-resistant. An example
of a common arrangement is shown in Fig. 6. Alternate configurations may be used.
7.5 Spray Chamber:
7.5.1 The spray chamber provides an aerosol droplet-sorting function to ensure that only the smaller droplets (typically less than
10 μm) reach the plasma. This ensures that the plasma is not significantly overloaded with solvent. The larger droplets are
condensed and drained away from the spray chamber. If a peristaltic pump is used to remove the waste liquid from the spray
chamber during nebulization, the pump tubing for the drain should be of a higher flow rating than that used for the intake.
Courtesy of Leeman Labs, Inc., 110 Lowell Rd., Hudson, NH 03051.
This nebulizer is sometimes misnamed a cross-flow nebulizer. It is most properly named a Babington or modified Babington nebulizer after the original and pertinent
patent holder.
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FIG. 6 Babington-Type Nebulizer
FIG. 7 Spray Chamber
7.5.2 A positive pressure must be maintained in the spray chamber to prevent air ingress and deliver the sample aerosol to the
torch. It Therefore, it is therefore vital to ensure that all connections between the spray chamber and the ICP torch are leak-proof
and that the drain plug is secure. If a peristaltic pump under computer control is incorporated, automatic start-up and shutdown
can be achieved without depleting sample solution.
7.5.3 A common ICP spray chamber is a double-pass-type fabricated of glass (see Fig. 7). If fluoride is present in solutions to
be analyzed, it is necessary to employ a spray chamber constructed from HF-resistant materials. It is possible to use the
HF-resistant spray chamber for other types of solutions.
7.6 Plasma Torch—The argon gas that forms the plasma is directed through the load coil by means of a plasma torch.
7.6.1 The classic ICP torch is constructed of three concentric quartz tubes sealed together and is known as a one-piece
‘one-piece’ or ‘fixed’ torch (see Fig. 8 ). These torches produce good plasma stability and are easy to use. However, they are, in
general, not HF-resistant and, if damaged, the entire torch must be replaced.
7.6.2 The demountable torch (see Fig. 9 ) is in common use particularly since the individual tubes can be replaced without
replacing the entire assembly.
7.6.3 Alternate construction materials of construction (typically ceramics) may be employed for analyzing solutions containing
significant quantities of fluoride ion that attacksattack quartz.
7.6.4 In place of quartz, one-piecefixed or demountable torches are commonly made of an HF-resistant ceramic. For
demountable torches, all tubes, or often only the central or injector tube, are made from a corrosion-resistant ceramic.
Courtesy of TJA Solutions, 27 Forge Parkway, Franklin, MA 01945.Spectro Analytical Instruments GmbH, Boschtr, 10 47533 Kieve, Germany.
Courtesy of TJA Solutions (formerly VG Elemental), Ion Path Road Three, Winsford Cheshire, CW7 3BX UK.Texas Scientific Products (TSP), 11941 Hilltop Rd., Suite
15, Argyle, TX.
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FIG. 8 Typical One-Piece Quartz Torch
FIG. 9 Demountable Torch
7.6.5 If fluoride-containing solutions are to be analyzed routinely, the design and performance of the prospective
supplier’smanufacturer’s HF-resistant torch should be evaluated.
7.6.6 There may be significant variations in the ease of concerning installation and operation, and in costs of repair and
maintenance.
7.6.7 Alternately, it may be possible to build an HF-resistant system or acquire one from a vendormanufacturer different than
the manufacturer of the spectrometer.
7.6.8 Before purchasing a third-party torch system, a demonstration of both repeated plasma initiationignition reliability and
analytical performance with the fluoride medium in the intended model spectrometer is recommended unless a satisfactory
guarantee of analytical performance and initiationignition reliability is obtained.
7.7 Gas Flow:
7.7.1 There are usually three gas flows through the torch. The first is the outer (coolant or plasma) gas flow which is directed
tangentially to the internal surface of the largest diameter portion of the torch (typically 12 L/min to 20 L/min,L/min although some
torches are designed to operate on much lower flow rates). Second, an intermediate (auxiliary) gas flow (typically 0.5 L/min to
1 L/min) is directed between the central tube through which the sample aerosol is introduced and the outer tube to reduce carbon
formation on the injector tip when organic samples are being analyzed and to prevent the plasma from collapsing onto the injector
tip. That intermediate flow, however, may also improve performance with aqueous samples. Third, an inner (sample or nebulizer)
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flow (typically 0.4 L/min to 1 L/min) passes through the sample introduction device and transports the analyte through the injector
tip into the plasma. The manufacturer should provide data on optimal ranges for each of the gas flows since torch geometry strongly
influences optimal rates.
7.7.2 An argon sheath attachment, a device for changing the flow rate of the intermediate flow during the analysis by introducing
an additional argon flow under computer control, is available. This additional flow affects the observation zone that is viewed by
the spectrometer and, consequently, for example, enhanced detection limits for the alkali metals and alkaline earths may be
realized. Furthermore, the argon sheath attachment may also prevent salt encrustation in the inner tube with elevated salt
concentration samples.
7.7.3 The inner gas flow rate is the most critical because it affects the injection efficiency and residence time of the sample in
the plasma and, especially for a pneumatic nebulizer (see 7.3), influences transport efficiency of both analyte and solvent species.
Both sensitivity and position of the maximum signal-to-noise ratio within the plasma are dependent on sample gas pressure and
flow rate.
7.7.4 A conventional regulator and rotameter provide adequate stability in most cases, but a precision pressure controller or
controller, a mass flow controller (MFC) or a volume flow controller (VFC) may be required in certain applications. Accordingly,
most modern instruments employ mass or volume flow controllers at least for the central or nebulizer flow or for all plasma gas
flows. The intermediate flow affects the vertical location of the plasma relative to the torch and load coil. Gross variations will
affect accuracy and precision but an MFC is seldom, if ever, required for this flow. An MFC also may be used for the inner gas
flow, but is seldom, if ever, required. The precision. If available, the user should compare results with and without MFCs to
determine their impact on performance.
7.7.5 In all but the most robust (all ceramic) torches, loss of outer gas flow through the torch will lead to rapid melting. A safety
interlock must be included in the instrument design to turn off power to the RF generator in case of loss of argon pressure.
7.8 Alternate Sample Introduction Devices:
7.8.1 Ultrasonic Nebulizer (USN):
7.8.1.1 A USN with desolvation is the most generally useful alternate sampling device. In this device, the sample solution is
pumped over the face of a quartz-coated crystalline transducer driven by a low-power RF generator (see Fig. 10). The apparatus
is about ten times as efficient as the self-aspirating and pumped pneumatic nebulizers described in 7.3 and 7.4, respectively, and
is useful for situations requiring very high sensitivity. Sensitivity is about ten times better with a USN than with self-aspirating
and pumped pneumatic nebulizers. However, the USN device is more expensive and may require more maintenance than the
pneumatic types.
7.8.1.2 Operation of the USN without desolvation is generally not practical because the large amount of aerosol reaching the
plasma creates an excessive solvent load which reduces excitation efficiency and negates all potential sensitivity advantage. The
aerosol, therefore, is passed through a heated zone followed by a condenser to limit solvent loading of the plasma.
FIG. 10 Ultrasonic Nebulizer
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7.8.1.3 Solutions with relatively high concentrations of dissolved solids or uncomplexed fluoride ion may not be suitable for
ultrasonic nebulization.
7.8.1.4 Ultrasonic nebulizers may be slightly less stable than pneumatic nebulizers although USN performances of between 0.5
% RSD and 1 % RSD are typical with recent versions. The user should ensure that short-term precision (≤1 % RSD for raw,
uncorrected, unratioed signals) and long-term drift rates are adequate for all anticipated applications.
7.8.2 Hydride Generation:
7.8.2.1 Hydride generation is useful for elements which may be converted to volatile hydrides. This technique affords improved
sensitivity and avoids interferences arising from spectral overlap with non-volatile concomitants.
7.8.2.2 Interference occurs instead in the form of chemical inhibition of the hydride reaction. Concentrated transition metal or
precious metal media or selected dissolved oxidants, or a combination thereof, produce the worst interferences. Combinations of
metal and certain oxidants (notably, nitricHNO acid and its residues) can be particularly troublesome because of metal-induced
catalytic effects which amplify the chemical inhibition. Optimization of reagent (reductant) concentration, generally lowering to
the range between 0.5 % and 1 % NaBH or less, can minimize or eliminate catalytic inhibition and frequently reduce the
magnitude of interference to a range where standard addition or matrix matching become at least usable calibration schemes.
7.8.2.3 Care must be taken Take care to match samples and reference materials and to ensure that analytes are converted to the
proper chemical form for quantitative conversion to the desired hydrides. Commercial equipment is available or the literature may
be consulted to design and build a suitable apparatus. While hydride generation was performed in a transient manner in older
atomic absorption systems, often the data acquisition systems of most commercially available ICP-AES systems are more
conducive to continuous generation.
7.8.3 Electrothermal Vaporization (ETV):
7.8.3.1 ETV may be employed where sample size is limited. As with hydride generation, the transient nature of ETV is not well
suited to conventional ICP-AES data acquisition systems and may not work at all with many such systems. ETV An efficient
application of ETV usually requires a (fully) simultaneous ICP-AES instrument with a sufficiently high data rate (typically 10 Hz)
for the ETV-generated transient analyte signals of interest. Accordingly, ETV is particularly unsuited to sequential spectrometer
systems because relatively slow wavelength change between sequentially determined elements precludes any possibility of
transient multielement ETV analysis on these systems. Because of extended dry and ash cycles, ETV systems have substantially
slower cycling times in terms of sample throughput rate.
7.8.3.2 Autosamplers for ETV are can be far more complex and expensive and aremight not be as readily available as they are
for gas nebulizers.pneumatic nebulizers. Still, commercial systems allowing automatic ETV processing of up to 50 samples are
available.
7.8.3.3 ETV precision is typically worse than that of gas nebulization and, therefore, requires a greater number of replicate
determinations. Also, the interference effects are more intricate and extensive. The prospective user of ETV should try the desired
analysis at the manufacturer’s application laboratory before purchasing an instrument.
7.8.4 Sampling Solid Materials—Approaches to direct analysis of solid materials include insertion of a graphite rod containing
the specimen into the plasma, arc or spark ablation, laser ablation, or slurry nebulization. Since considerable skill is required, these
techniques cannot be recommended for the beginner or casual user. Commercial devices are available, but the prospective user
should evaluate them critically before purchase to ensure that the required sensitivity, precision, and accuracy may be attained in
the sample medium of interest. Considerable care is required in selecting appropriate reference materials for accurate calibration.
7.9 Autosamplers—For situations in which large numbers of similar samples are to be analyzed, an automated sample
introduction system may be desirable. Such a device may be purchased from the manufacturer of the spectrometer or acquired from
another supplier.
7.9.1 Two types of autosamplers are generally available. The simpler and less costly is a sequential device that processes
samples in the sequence in which they are loaded into a rack prior to starting analysis. More sophisticated devices allow random
access. This capability may beusually is coupled with an appropriate computer hardware/software system system, or preferably
directly integrated into the ICP-AES instrument software to allow recalibration if results for quality control check standardsma-
terials are not within a specified range, or to repeat analyses if duplicates do not agree within acceptable limits of precision. If the
user wishes to acquire an autosampler from a source other than the instrument vendor,manufacturer, the compatibility and software
integration capability must be verified by consultation with the manufacturer of the spectrometer, and preferably by actual product
demonstration.
8. Spectrometers
8.1 ICP spectrometers may be classified as sequential types, simultaneous types, a combination of the two called
simultaneous/sequential systems, and solid state detector spectrometers.either employing a ‘classical’ photomultiplier tube (PMT)
as detector, or a solid state detector. Most of the commercial instruments available currently utilize semiconductor solid state
detectors, mainly in conjunction with simultaneous or simultaneous/sequential spectrometers, where the latter, for example, allows
for the simultaneous detection of a certain wavelength interval around the analyte emission line(s) or even a larger spectral region.
8.1.1 Sequential Spectrometers—Spectrometers with PMT(s)—Perform determinations by means of a monochromator and one
or more photomultipliers. Commercially available instruments may select the wavelength to be monitored either by rotating the
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grating of the monochromator or moving the photomultiplier tube. Some spectrometers contain more than one monochromator or
detector to improve rate of data acquisition or to optimize performance in each of several spectral regions, or both. In addition,
a second monochromator may monitor a reference wavelength, thus permitting real-time internal standardization for improved
precision.
8.1.2 Simultaneous Spectrometers—Spectrometers with PMT(s)—Conventional simultaneous spectrometers usually employ one
or more separate exit slits and photomultiplier tubes for each element of interest. A typical polychromator consists of an entrance
slit, a diffraction grating, and exit slits located on the focal curve with a photomultiplier tube behind each exit slit. Alternatively,
the exit slits and photomultiplier tubes may be replaced by a solid state detector (see 9.3). Some spectrometers have an auxiliary
monochromator to allow determination of at least one additional element not detected by the array of photomultipliers mounted
on the focal curve.
8.1.3 Combined Spectrometers—Spectrometers with PMT(s)—Some photomultiplier tube-based instruments include each type
of spectrometer described in 8.1.1 and 8.1.2. This design combines the advantages of the superior speed, excellent precision, and
simultaneous multielement analysis attainable with a simultaneous instrument and the flexibility to measure the emission at any
suitable ultraviolet or visible wavelength using a sequential scanning spectrometer.
8.1.4 Solid State Detector Spectrometers—Several, usually simultaneous, spectrometer designs can be combined with solid state
detectors advantageously and are available commercially. Echelle spectrometers are available to provide high resolution in a
compact x-y wavelength presentation format. The compact format allows imaging of the spectrum onto one or more silicon wafer
array detectors including photodiode arrays (PDA), charge coupled device (CCD) arrays and charge injection device (CID) arrays
containing anywhere from several thousand to over 250,000 individual pixels. Such advanced array detectors can theoretically be
fitted with an image intensifier plate, but are typically operated at unity gain to control costs. Echelle-based spectrometers can
either allow simultaneous ‘full’ spectrum capture or – in the form of an ‘Echelle Monochromator’– the simultaneous capture of
a small wavelength region around the analytical emission line of interest, typically sufficient for simultaneous background
correction. Also, Echelle-based ‘full spectrum’ systems are commercially available that cover the relevant emission spectrum in,
for example, two integrations, each consisting of about half of the full spectral range.
8.1.4.1 Spectrometers based on the Paschen-Runge Mount, with a single or several concave diffraction gratings and a number
of linear solid state detector arrays arranged around the Rowland Circle to detect the wavelength dispersed radiation within a single
diffraction order (usually the 1st only) reach a high and constant spectral resolution over large wavelength ranges. The lack of
transmission optical components as, for example, a prism for order sorting, allows for deep UV spectral performance, down to 130
nm in some commercial intruments. Like Echelle systems, Paschen-Runge systems that capture the full spectral range in several
(typically two) individual integrations also exist. Finally, solid state detector systems based on a Czerny-Turner Monochromator
permitting the capture of the analyte emission and a certain wavelength interval around it simultaneously exist commercially.
8.1.4.2 Except for being used as a simultaneous spectrometer, solid state detectors have some distinct differences to other
spectrometers.
8.1.4.3 The For Echelle-based systems, the lack of detector gain above unity and the compact echelle format, which is
characterized by the unusually short slit height required for prismatic order sorting collectively have an adverse effect on system
sensitivity unless offsetting factors are introduced.
8.1.4.4 Successful offsetting (compensating) factors include various combinations of increased integration time (exposure time),
detector cooling, improved spectrometer f/number (numerical aperture), and axial viewing of a horizontally oriented plasma torch.
8.1.4.5 Similarly for the other solid state detector spectrometer designs described and commercially available, an adaption of
spectrometer and detector parameters, for example, de-magnification of the diffraction plane image onto the light-sensitive detector
part can offset the results from geometric and detector gain differences between PMTs and solid state detectors.
8.1.4.6 In at least one case, a combination of the above four parameters consistently yielded routine sensitivity for an advanced
array detector equaling that of photomultiplier tubes. This is also proven by the fact that the majority of ICP-AES instruments sold
commercially currently utilize solid state detection, for the advantages described below.
8.1.4.7 An advantage of advanced array detectors is substantially larger numbers of simultaneously determined elements. In
many cases two or more analytical spectral lines may be simultaneously monitored. Other advantages include: simultaneous
background correction adjacent to every spectral line is easily performed and offers potentially greater accuracy; alternate line
selection provides more flexibility to minimize or avoid spectral interference, or to increase the overall system concentration
dynamic range for a given element with both strong and weak lines are available for many elements, or both; and, availability of
chemometric enhancement of signal to noise ratio using multiple lines of each element.element, including (full-spectrum)
modelling approaches for spectral interference correction. Finally, the availability of a complete spectrum with each measurement
opens the possibility for retrospective analysis, for example, detection of elements present in the sample not included in the original
analytical program.
8.1.4.8 Short wavelength sensitivity inherently varies from one device type to the next and for many years was a severe
limitation. Modern silicon wafer technology can improve poor UV photosensitivity limits by either elimination of the surface oxide
dead layer during manufacture or by phosphor coatings. By either means, several systems are available with spectral response
extending easily to wavelengths less than 167 nm, down to 130 nm.
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8.1.4.9 Considerations in selecting an advanced array detector system should include spectral resolution, sensitivity for all
elements of interest, particularly elements that give rise to short wavelength emissions, the number of available detector pixels,
and the number of elements that can be simultaneously determined in the sample medium of interest. Often, the largest number
of pixels does not guarantee the best results. Resolution sensitivity must be considered in the sample medium of interest.
8.2 Spectrometer Environment:
8.2.1 Temperature fluctuations affect instrument stability. Some manufacturers provide systems for maintaining a constant
internal temperature within the optical compartment and sample introduction area provided that changes in the outside temperature
are controlled within a specified range and rate of change. Other manufacturers design their spectrometers to be stable over a
specified temperature range without attempting to control the spectrometer’s internal temperature.
8.2.2 Changes in the refractive index of the atmosphere affect the optical path. Manufacturers provide various means to
compensate for these changes, including use of evacuated (vacuum), sealed gas-filled, purged, or precise, pressure-controlled,
gas-purged spectrometers, or use of optical compensation as follows:
8.2.2.1 Simultaneous instruments are can be equipped with movable entrance slits or a rotating refractor plate behind the slit
to shift the image of the entrance slit onto the exit slits,slits. If equipped with a suitable ‘full spectrum’ detector (normally a solid
state detector(s) array), simultaneous spectrometers may utilize a full-spectrum pattern matching algorithm to compensate for
wavelength drift, using, for example, known emission line positions from a known reference sample or plasma background
emissions (for example, Ar lines).
8.2.2.2 Sequential spectrometers may be designed to locate an intense reference line before each measurement and then, under
computer control, make measurements at a predetermined wavelength distance from that reference line for each spectral line to
be measured, or
8.2.2.3 The sequential spectrometer may be designed to move in turn to each approximate wavelength and perform a peak
search before taking the measurement.
8.2.3 For all designs, it is necessary to provide internal temperature control, or to design and construct the spectrometer so that
stability may be achieved without temperature control.
8.2.4 Since temperature and humidity changes may also affect the sample introduction system, detectors, and electronic readout,
some manufacturing specifications may require that care be used in selecting a location for the spectrometer which experiences
minimal variation in temperature and relative humidity. It is the responsibility of the user to provide a controlled environment as
specified by the manufacturer.
8.3 Optical Path:
8.3.1 Since oxygen exhibits increasing absorbance with decreasing wavelength below 200 nm, the performance of an air path
instrument degrades below that wavelength and generally is not useful below approximately 190 nm.
8.3.1.1 Purging the optical path with nitrogen or argon, or another gas with low absorption in the ultraviolet region may extend
the spectral region to wavelengths less than 167 nm. Use of nitrogen as the purge gas is, in general, less expensive to maintain
than vacuum path systems. Purge rates required to achieve a given performance level (below 200 nm) vary widely according to
the manufacturing design of the spectrometer, volume to be purged, and the extent of leaks in the spectrometer housing. Before
purchase, it is advisable to check the purge gas rate (L/min) required to achieve specified detection limits below 200 nm.
8.3.1.2 Alternatively, the spectrometer optical compartment may be purged with nitrogen, nitrogen or argon, sealed and
maintained at a lowconstant pressure. The nitrogen or argon is continuously filtered over reactive catalysts to scrub out oxygen and
water. With modification to certain optical components in the spectrometer, wavelengths can be extended to 120 nm.
8.3.1.3 Vacuum path instruments are more expensive and require additional maintenance.
8.3.1.4 For purged, closed purged and vacuum systems, isolation of the optics from the laboratory environment will lengthen
the useful lifetime of mirrors, gratings, and refractor plates (if present), especially if the environment contains significant
concentrations of acid fumes.
8.3.1.5 If purging or vacuum are operated continuously, there is no effect on data acquisition rate once equilibrium has been
achieved in the spectrometer. Alternatively, with proper design and construction, a vacuum spectrometer may include a feedback
system to turn the vacuum pump on when an upper limit of about 10 Torr is excee
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