ASTM E863-98(2004)e1
(Practice)Standard Practice for Describing Flame Atomic Absorption Spectroscopy Equipment (Withdrawn 2004)
Standard Practice for Describing Flame Atomic Absorption Spectroscopy Equipment (Withdrawn 2004)
SCOPE
1.1 This practice covers those features that are important for evaluating atomic absorption spectroscopy equipment. It also discusses performance characteristics and identifies parameters that should be recorded in analytical procedures.
1.2 This standard does not purport to address all of the safety problems, 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 warning statements are given in the Note in 5.3 and specific precautionary statements are given in Section 7.
WITHDRAWN RATIONALE
This practice covers those features that are important for evaluating atomic absorption spectroscopy equipment. It also discusses performance characteristics and identifies parameters that should be recorded in analytical procedures.
Formerly under the jurisdiction of Committee E01 on Analytical Chemistry for Metals, Ores and Related Materials, this practice was withdrawn because it is no longer practiced.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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e1
Designation:E863–98 (Reapproved 2004)
Standard Practice for
Describing Atomic Absorption Spectrometric Equipment
This standard is issued under the fixed designation E 863; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Warning notes were editorially moved into the standard text in August 2004.
1. Scope 5. Description of Equipment
1.1 Thispracticecoversthosefeaturesthatareimportantfor 5.1 Optical System—Both single-beam and double-beam
evaluating atomic absorption spectroscopy equipment. It also optical systems are in use.Asingle-beam system employs one
discusses performance characteristics and identifies parameters opticalpathtomeasurebothincidentandtransmittedradiation.
that should be recorded in analytical procedures. The two measurements are separated in time. A double-beam
1.2 This standard does not purport to address all of the system separates the incident radiation into two portions. One
safety concerns, if any, associated with its use. It is the of these portions (often designated I) is measured after travers-
responsibility of the user of this standard to establish appro- ing the analytical cell; the other portion (often designated I )
o
priate safety and health practices and determine the applica- represents the radiation incident on the analytical cell. Signals
bility of regulatory limitations prior to use. Specific warning from the two portions are used to compensate for baseline
statements are given in 5.3 and specific precautionary state- variability. In single-beam systems, instability of either the
ments are given in Section 7. incident intensity or the detector-amplifier sensitivity-gain
contributes to the variability of the signal. Double-beam
2. Referenced Documents
systems can correct completely for either type of instability.
2.1 ASTM Standards:
Neither single-beam nor double-beam systems can correct for
E 135 Terminology Relating to Analytical Chemistry for fluctuations occurring in the flame.
Metals, Ores, and Related Materials
5.2 Radiation Sources—The most widely used source of
E 416 Practice for Planning and Safe Operation of a Spec- absorbing lines is the hollow cathode lamp. It emits narrow
trochemical Laboratory
spectral lines, has low background, and is applicable to
E 520 Practice for Describing Photomultiplier Detectors in virtually all elements amenable to atomic absorption analysis.
Emission and Absorption Spectrometry
Thehigh-frequencyelectrodelessdischargelamp(EDL)isalso
E 1770 Practice for Optimization of ElectrothermalAtomic
an excellent source of sharp line spectra. It provides more
Absorption Spectrometric Equipment intensity than the hollow cathode lamp, but is not as univer-
E 1812 Practice for Optimization of FlameAtomicAbsorp-
sally applicable. EDLs require a special power supply.
tion Spectrometric Equipment 5.2.1 The hollow cathode lamp shall emit stable, low-drift
radiation of usable intensity, free of interfering spectral lines
3. Terminology
due to filler gas or cathode impurities.
3.1 For definitions of terms used in this practice, refer to
5.2.2 Stability—Intensity drift shall not exceed 3 % per 15
Terminology E 135.
min after a 30-min warm up. Many lamps available now are
better than 1 % per 15 min after warm up.
4. Significance and Use
5.2.3 Lamp Life—The hollow cathode lamp or EDL shall
4.1 This practice provides criteria for instrument selection
maintain the above characteristics over the manufacturer’s
and should be useful for setting up an atomic absorption
warranted life. The expected life of hollow cathode lamps is
facility.
approximately 5 Ah.
5.3 Flames—Flames are classified as diffusion or premixed.
The characteristics of the diffusion flame are determined by the
This practice is under the jurisdiction of ASTM Committee E01 on Analytical
rate at which the fuel diffuses into the ambient oxygen or the
Chemistry for Metals, Ores and Related Materials and is the direct responsibility of
oxidant supplied through a separate orifice. In the premixed
Subcommittee E01.20 on Fundamental Practices.
Current edition approved July 1, 2004. Published August 2004. Originally
approved in 1982. Last previous edition approved in 1998 as E 863 - 98.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM “Guidelines for the Purity and Handling of Gases Used in Atomic Absorption
Standards volume information, refer to the standard’s Document Summary page on Spectroscopy”, AI2.1a, 1978, Scientific Glass Makers Association, 1140 Connecti-
the ASTM website. cut Ave., N.W., Washington, DC 20036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E863–98 (2004)
flame, the characteristics are determined by the kinetics of the ing popular. The nebulizer efficiency, or the fraction of the
chemicalcombustionproducingtheflame.Ingeneral,diffusion aspirated solution that actually reaches the flame, shall be
flames are more turbulent than pre-mixed flames and the flame
specified for pre-mix nebulizer burner systems. The efficiency
reactions are not spatially resolved. Premixed acetylene and air
isafunctionoftheratesofsolutionuptakeandofthedischarge
or acetylene and nitrous oxide flames are the most commonly
through the drain tube.
used atomic absorption flames.Acetylene is the most common
5.4.2 Gas Flow Controls—Stable flame operation depends
fuel. Hydrogen, natural gas, propane, and similar fuels are
on reproducible and stable flow of fuel and oxidant gases. A
sometimesusedtoproducecoolerflames.Airandnitrousoxide
minimal system shall have a two-stage regulating device at the
are the normal oxidants. Oxygen has sometimes been used, but
fuel source and at the oxidant source. There shall be a pressure
due to higher flame propagation velocities, it is not used
meter for the nebulizing gas, a flow meter for each gas, and a
anymore. (Warning—Never use copper tubing for acetylene
flow control system for each gas line at the burner.
because of the possible formation of explosive copper acetyl-
5.4.2.1 The manufacturer shall specify suitable gas flows.
ide.)
Flow meters should be calibrated in litres per minute or some
5.4 Burners—Historicallytwotypesofburnerswereusedin
comparable unit. If the burner system is to be used with a
atomic absorption spectroscopy, the direct injection or total
nitrous oxide acetylene flame, special precautions to avoid
consumption burner and the pre-mix nebulizer burner. The
flashback when the flame is ignited and extinguished, shall be
total consumption burner ensures freedom from flashbacks and
provided. The gas control system shall allow the oxidant to be
was once popular for flame spectroscopy. However, it has
changed from air to nitrous oxide and back again without
serious disadvantages such as high noise levels, lack of distinct
interruption of flow to the burner. The flame shall be ignited
flame zones, high background emission, and difficulties in
using air and acetylene, then switched to nitrous oxide. The
obtaining flame shape suitable for absorption measurement,
reverse procedure shall be followed when the flame is extin-
and, therefore is no longer being used. The most widely used
guished. Some instruments have systems that automatically
burner now is the pre-mix nebulizer burner. In this burner, a
small fraction of the aspirated solution reaches the flame. Only provide the startup-shutdown sequence, monitor gas flows, and
the very finest droplets are used, which makes this an energy- shut down automatically if the gas flows are outside a
efficientsystem.Theburnerproducesahigh-temperatureflame
prescribed range.
with relatively low emission background or noise. The flame
5.5 Electrothermal Atomizers—Most flame atomic absorp-
can be shaped to provide for a long light path through it. A
tion spectrometers manufactured currently can be easily
serious disadvantage is that the pre-mix chamber contains an
adaptedforelectrothermalanalysis,whilesomeatomicabsorp-
explosive gas mixture during operation. An explosive flash-
tion spectrometers are dedicated to electrothermal analysis.
backispossiblewhentheburningvelocityexceedsthevelocity
5.5.1 The most commonly used electrothermal atomizer is
of the burning gases passing through the burner orifice.
the graphite tube furnace. This atomizer consists of a graphite
Equipment shall be designed to minimize the probability of a
tube positioned in a water-cooled unit designed to be placed in
flashback, protect the instrument operator and anyone nearby
the optical path of the spectrophotometer so that the light from
from injury if a flashback does occur, and minimize damage to
the hollow cathode lamp passes through the center of the tube.
the burner, chamber, and instrument.
The tubes vary in size depending upon a particular instrument
5.4.1 Nebulizers—The nebulizer is used to aspirate the
manufacturer’s furnace design. These tubes are available with
sample and convert it to a fine mist. The most common
or without pyrolytic graphic coating. However, because of
nebulizers employ oxidant gas as the source of energy for
increased tube life, tubes coated with pyrolytic graphite are
nebulization. The mist consists of a wide distribution of
commonly used. The water-cooled unit or atomizer head that
particle sizes but only the smallest (less than 1 µm in diameter)
holds the graphite tube is constructed in such a way that an
reach the flame and contribute to the atomic absorption signal.
inert gas, usually argon or nitrogen, is passed over, around, or
Some pre-mix chambers employ an impingement bead to
through the graphite tube to protect it from atmospheric
enhance the generation of smaller particles, and mix the gases
oxidation.Theheatingofalloftheseatomizersiscontrolledby
and vapors before passing through the burner slots. Other
power supplies that make it possible to heat the graphite tube
pre-mix chambers enhance particle size separation by baffles
to 3000°C in less than 1 s. Temperatures and drying, pyrolysis,
thatallowonlythefinestparticlestoreachtheflame.Theresult
and atomization times are controlled by these power supplies.
is a smaller but more stable absorption signal. Ultrasonic
nebulizers have been used experimentally for fog generation.
5.6 Automatic Background Correction—Automatic back-
They provide an efficient generation of a uniform mist. In
ground correction is recommended for all atomic absorption
practice, however, such problems as feeding the sample uni-
units.
formly, conducting the vapor to the burner, and sample
5.6.1 Automatic background correction is a necessity for all
memory have prevented this nebulization system from becom-
spectrophotometers used with electrothermal devices. When
electrothermal atomizers, especially graphite furnaces, are
4 heated to high temperatures, background from absorption is
Kirkbright, G. F., and Sargent, M., Atomic Absorption and Fluorescence
Spectroscopy, Academic Press, New York, NY, 1974, p. 201. produced within the graphite tube. Also, small amounts of
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E863–98 (2004)
particulate matter in the furnace contribute to the background expressed in nanometres per millimetre as defined in Termi-
signal. Therefore, it is essential to correct or compensate for nology E 135. If dispersion changes significantly with wave-
this background. length, the wavelength at which the value is given shall be
5.6.1.1 Magnetic (Zeeman type) background correction specified.
gives a wider range of correction than hydrogen or deuterium
5.7.5 Wavelength Range of the Spectrometer—The effective
backgroundcorrectorsandisapreferredtypeforspectrometers
wavelength range of the spectrometer is a function of the
using electrothermal atomization.
monochromator, the detector, and the medium through which
5.7 Spectrometer—The wavelength where absorption mea-
the optical path passes. The minimum and maximum wave-
surements are made is isolated from the total spectrum of the
lengths at which the monochromator optics can be set shall be
primary radiation source by means of a monochromator, or by
specified. If this wavelength range can be varied by inter-
nondispersive devices.
changeable gratings or prisms, it shall be so stated, and the
5.7.1 Monochromator Types—Monochromators are prima-
minimum and maximum values given. The usable wavelength
rily classified as to whether the wavelength-discriminating
range of the overall system, including the detector, will usually
function is performed by a grating, a prism, optical filters of
belimitedatthelowerwavelengthbythespectralabsorptionof
various types ranging from single glass filters to multilayer
the ambient atmosphere and optics, and at the higher wave-
interference filters (transmission or reflection types), or a
length by spectral sensitivity of the detector. Descriptions of
combinationofgratingandprism,suchasmaybeusedinsome
systemsshalldifferentiatebetweenthewavelengthrangeofthe
double monochromators.
monochromator and the usable wavelength range of the overall
5.7.1.1 Optical Design of Monochromators—Grating and
system.
prism monochromators are further classified by the optical
5.7.6 Wavelength Scanning—If the monochromator pro-
configuration of the incident and dispersed beams. Such
vides for scanning the wavelength range at a predetermined
configurations include the Czerny-Turner, Ebert, Eagle, Lit-
rate, it shall be so specified.The following parameters describe
trow, and Littrow-Echelle mounts, used singly or in combina-
the scanning functions: single speed, multiple speeds, or
tion.Thevarioustypesdifferintheapplicationorconfiguration
continuously variable scanning speeds. The minimum and
of the collimating and dispersing elements, or both. The
maximum speeds expressed in nanometres per second or
different configurations take into account optical speed, disper-
nanometres per minute should be stated, as should the specific
sion, stability, optical defects, and astigmatism. There is no
values of scanning speeds.
overwhelmingly superior configuration.
5.7.7 Wavelength Accuracy—The maximum distance in na-
5.7.1.2 Description of the Grating shall include the follow-
nometres between an indicated wavelength and the mean
ing information: (1) Type: plane or concave; (2) Size: width
wavelength passed by the monochromator at that setting shall
and height of ruled area expressed in millimetres; (3) Groove
be specified along with the wavelength range over which the
spacing: grooves per millimetre; and (4) Blaze wavelength:
...
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