ASTM D4691-17

Standard Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry

SIGNIFICANCE AND USE
5.1 Elemental constituents in water and wastewater need to be identified to support effective water quality monitoring and control programs. Currently, one of the most widely used and practical means for measuring concentrations of elements is by atomic absorption spectrophotometry.  
5.2 The major advantage of atomic absorption over atomic emission is the almost total lack of spectral interferences. In atomic emission, the specificity of the technique is almost totally dependent on monochromator resolution. In atomic absorption, however, the detector sees only the narrow emission lines generated by the element of interest.
SCOPE
1.1 This practice covers general considerations for the quantitative determination of elements in water and waste water by flame atomic absorption spectrophotometry. Flame atomic absorption spectrophotometry is simple, rapid, and applicable to a large number of elements in drinking water, surface waters, and domestic and industrial wastes. While some waters may be analyzed directly, others will require pretreatment.  
1.2 Detection limits, sensitivity, and optimum ranges of the elements will vary with the various makes and models of satisfactory atomic absorption spectrometers. The actual concentration ranges measurable by direct aspiration are given in the specific test method for each element of interest. In the majority of instances the concentration range may be extended lower by use of electrothermal atomization and conversely extended upwards by using a less sensitive wavelength or rotating the burner head. Detection limits by direct aspiration may also be extended through sample concentration, solvent extraction techniques, or both. Where direct aspiration atomic absorption techniques do not provide adequate sensitivity, the analyst is referred to Practice D3919 or specialized procedures such as the gaseous hydride method for arsenic (Test Methods D2972) and selenium (Test Methods D3859), and the cold vapor technique for mercury (Test Method D3223).  
1.3 Because of the differences among various makes and models of satisfactory instruments, no detailed operating instructions can be provided. Instead the analyst should follow the instructions provided by the manufacturer of a particular instrument.  
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversion to inch-pound units that are provided for information only and are not considered standard.  
1.5 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. For specific hazard statements see Section 9.  
1.6 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.

General Information

• Status: Published
• Publication Date: 31-May-2017
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Refers: ASTM D3859-15(2023) - Standard Test Methods for Selenium in Water
• Effective Date: 01-Dec-2023
• Refers: ASTM D2972-15(2023) - Standard Test Methods for Arsenic in Water
• Effective Date: 01-Dec-2023
• Refers: ASTM E520-08(2023)e1 - Standard Practice for Describing Photomultiplier Detectors in Emission and Absorption Spectrometry
• Effective Date: 01-Apr-2023
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D3223-17 - Standard Test Method for Total Mercury in Water
• Effective Date: 01-Jun-2017
• Refers: ASTM D4453-17 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 01-Feb-2017
• Refers: ASTM E178-16 - Standard Practice for Dealing With Outlying Observations
• Effective Date: 01-Jun-2016
• Refers: ASTM D4453-16 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 15-Feb-2016
• Refers: ASTM D3859-15 - Standard Test Methods for Selenium in Water
• Effective Date: 15-Mar-2015
• Refers: ASTM D2972-15 - Standard Test Methods for Arsenic in Water
• Effective Date: 01-Feb-2015
• Refers: ASTM D3223-12 - Standard Test Method for Total Mercury in Water
• Effective Date: 01-Sep-2012
• Refers: ASTM D5810-96(2011) - Standard Guide for Spiking into Aqueous Samples
• Effective Date: 01-May-2011
• Refers: ASTM D4453-11 - Standard Practice for Handling of High Purity Water Samples
• Effective Date: 01-Feb-2011
• Refers: ASTM D3370-10 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010

Overview

ASTM D4691-17: Standard Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry provides a comprehensive methodology for determining elemental concentrations in water and wastewater. This ASTM standard is essential for laboratories and industrial operators involved in water quality monitoring, compliance testing, and environmental control. Using flame atomic absorption spectrophotometry (FAAS), this practice enables identification and quantitation of various elements commonly found in drinking water, surface waters, and both domestic and industrial waste streams.

Key Topics

• Element Quantification: The standard outlines best practices for quantitatively measuring a broad range of inorganic elements in water samples.
• Spectrophotometry Advantages: FAAS is highlighted for its rapidity, simplicity, and reduced spectral interferences compared to atomic emission techniques, making it a widely-used laboratory method.
• Detection Limits: Factors affecting detection sensitivity, such as instrument model, wavelength selection, and sample preparation techniques like pre-concentration or solvent extraction, are discussed.
• Sample Handling and Preservation: Guidelines stress the importance of contamination control, sample preservation (typically acidification), and appropriate storage to maintain sample integrity.
• Quality Control (QC): Quality control requirements include instrument calibration using multiple standards, verification of calibration, and ongoing QC checks with laboratory control samples to ensure analytical accuracy.
• Interference and Correction: The standard details methods for dealing with chemical and spectral interferences inherent to flame atomic absorption and offers recommendations for flame optimization and appropriate sample matrix matching.

Applications

ASTM D4691-17 is widely applied in contexts where reliable water analysis is paramount. Key application areas include:

• Water Quality Monitoring: Municipalities, utilities, and regulatory bodies use FAAS for routine monitoring of inorganic contaminants in drinking water and source waters to ensure compliance with health and environmental standards.
• Environmental Assessment: Laboratories performing environmental impact assessments apply this method to determine levels of trace metals and other elements in surface waters, groundwaters, and wastewater discharges.
• Industrial Wastewater Testing: Industrial facilities utilize FAAS to measure and control the concentrations of metals and other elements in process wastewater, aiding in regulatory compliance and pollution prevention.
• Research and Development: Academic and commercial research labs leverage this practice for investigations into water chemistry, trace element behavior, or method validation studies.

Related Standards

Compliance and integration with related ASTM standards and terminology is emphasized throughout ASTM D4691-17. Key related documents include:

• ASTM D1193: Specification for Reagent Water, defining water purity requirements for laboratory analyses.
• ASTM D2972, D3223, D3859: Specific test methods for arsenic, mercury, and selenium in water, supplementing instances where flame atomic absorption may not provide adequate sensitivity.
• ASTM D3919: Practice for Measuring Trace Elements in Water by Graphite Furnace Atomic Absorption Spectrophotometry, for lower detection limits.
• ASTM D4453: Practice for Handling of High Purity Water Samples, ensuring minimized contamination.
• ASTM D3370: Practices for Sampling Water from Closed Conduits, guiding proper sampling techniques.
• ASTM D1129: Terminology Relating to Water, providing definitions critical to understanding and applying water analysis standards.

Summary

By adopting ASTM D4691-17, laboratories and operators gain access to a robust and internationally recognized approach to water and wastewater elemental analysis. The flame atomic absorption spectrophotometry method ensures sensitive, accurate, and interference-minimized results, supporting regulatory compliance, environmental monitoring, and public health protection. For enhanced quality assurance, practitioners are encouraged to reference associated standards and maintain stringent QC procedures as outlined by ASTM.

Keywords: ASTM D4691-17, Flame Atomic Absorption Spectrophotometry, water analysis, elemental measurement, water quality, wastewater, laboratory standards, environmental compliance, sample preservation, quality control, FAAS

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: D4691 − 17
Standard Practice for
Measuring Elements in Water by Flame Atomic Absorption
Spectrophotometry
This standard is issued under the fixed designation D4691; 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* conversion to inch-pound units that are provided for informa-
tion only and are not considered standard.
1.1 This practice covers general considerations for the
1.5 This standard does not purport to address all of the
quantitative determination of elements in water and waste
safety concerns, if any, associated with its use. It is the
water by flame atomic absorption spectrophotometry. Flame
responsibility of the user of this standard to establish appro-
atomic absorption spectrophotometry is simple, rapid, and
priate safety, health, and environmental practices and deter-
applicable to a large number of elements in drinking water,
mine the applicability of regulatory limitations prior to useFor
surface waters, and domestic and industrial wastes. While
specific hazard statements see Section 9.
some waters may be analyzed directly, others will require
1.6 This international standard was developed in accor-
pretreatment.
dance with internationally recognized principles on standard-
1.2 Detection limits, sensitivity, and optimum ranges of the
ization established in the Decision on Principles for the
elements will vary with the various makes and models of
Development of International Standards, Guides and Recom-
satisfactory atomic absorption spectrometers. The actual con-
mendations issued by the World Trade Organization Technical
centration ranges measurable by direct aspiration are given in
Barriers to Trade (TBT) Committee.
the specific test method for each element of interest. In the
2. Referenced Documents
majority of instances the concentration range may be extended
lower by use of electrothermal atomization and conversely
2.1 ASTM Standards:
extended upwards by using a less sensitive wavelength or
D1129Terminology Relating to Water
rotating the burner head. Detection limits by direct aspiration
D1193Specification for Reagent Water
may also be extended through sample concentration, solvent
D2972Test Methods for Arsenic in Water
extraction techniques, or both. Where direct aspiration atomic
D3223Test Method for Total Mercury in Water
absorption techniques do not provide adequate sensitivity, the
D3370Practices for Sampling Water from Flowing Process
analyst is referred to Practice D3919 or specialized procedures
Streams
such as the gaseous hydride method for arsenic (Test Methods
D3859Test Methods for Selenium in Water
D2972) and selenium (Test Methods D3859), and the cold
D3919Practice for Measuring Trace Elements in Water by
vapor technique for mercury (Test Method D3223).
Graphite Furnace Atomic Absorption Spectrophotometry
D4453Practice for Handling of High Purity Water Samples
1.3 Because of the differences among various makes and
D5810Guide for Spiking into Aqueous Samples
models of satisfactory instruments, no detailed operating in-
D5847Practice for Writing Quality Control Specifications
structions can be provided. Instead the analyst should follow
for Standard Test Methods for Water Analysis
the instructions provided by the manufacturer of a particular
E178Practice for Dealing With Outlying Observations
instrument.
E520Practice for Describing Photomultiplier Detectors in
1.4 The values stated in SI units are to be regarded as
Emission and Absorption Spectrometry
standard. The values given in parentheses are mathematical
E863Practice for Describing Atomic Absorption Spectro-
metric Equipment (Withdrawn 2004)
1 2
This practice is under the jurisdiction ofASTM Committee D19 on Water and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Water. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 1, 2017. Published June 2017. Originally the ASTM website.
approved in 1987. Last previous edition approved in 2011 as D4691–11. DOI: The last approved version of this historical standard is referenced on
10.1520/D4691-17. www.astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4691 − 17
3. Terminology ies with instrumental conditions and atomization efficiency, as
well as other factors and should be determined as conditions
3.1 Definitions:
change. The characteristic concentration is determined by the
3.1.1 For definitions of terms used in this standard, refer to
following equation:
Terminology D1129.
characteristicconcentration 5 C 30.0044/A (1)
3.2 Definitions of Terms Specific to This Standard:
3.2.1 absorbance, n—the logarithm to the base 10 of the
where:
reciprocal of the transmittance ( T). A=log (1/T)=−log T.
10 10
C = concentration of the analyte, and
A = absorbance of analyte concentration used in the deter-
3.2.2 absorptivity, n—the absorbance (A) divided by the
productofthesamplepathlength(b)andtheconcentration(c). mination.
a= A/bc.
The characteristic concentration defines the slope of the
3.2.3 atomic absorption, n—the absorption of electromag- calibration curve.
netic radiation by an atom resulting in the elevation of
3.2.12 spectral bandwidth, n—the observed dispersion be-
electrons from their ground states to excited states.
tween absorption bands.
3.2.3.1 Discussion—Atomic-absorption spectrophotometry
3.2.12.1 Discussion—This bandwidth is expressed as the
involves the measurement of light absorbed by atoms of
exit slit multiplied by the observed separation of two emission
interest as a function of the concentration of those atoms in a
lines divided by the difference in wavelength between these
particular solution.
lines.
3.2.4 continuing calibration blank, n—asolutioncontaining
3.2.13 spectrophotometer, n—an instrument that provides
noanalytes (of interest)whichisusedtoverifyblankresponse
the ratio, or a function of the ratio, of the radiant power of a
and freedom from carryover.
beam as a function of spectral wavelength.
3.2.5 continuing calibration verification, n—a solution (or
setofsolutions)ofknownconcentrationusedtoverifyfreedom
4. Summary of Practice
fromexcessiveinstrumentaldrift;theconcentrationistocover
4.1 In flame atomic absorption spectrophotometry, a stan-
the range of calibration curve.
dard or sample solution is aspirated as a fine mist into a flame
3.2.6 detection limit, n—in atomic absorption, a function of
where it is converted to an atomic vapor consisting of ground
thesensitivityandthesignal–to–noiseratiointheanalysisofa
state atoms. The flame provides energy to the ground state
specific element for a given set of parameters.
atoms allowing them to absorb electromagnetic radiation from
3.2.6.1 Discussion—The instrument detection limit is deter-
a series of very narrow, sharply defined wavelengths. Light
minedstatisticallyassomemultiple,usuallytwoorthreetimes
(fromahollowcathodelamporothersource)consistingofthe
the standard deviation of the signal-to-noise ratio.
characteristicmonochromaticradiationgeneratedbyexcitation
of the element of interest is passed through the flame. Light
3.2.7 laboratory control sample (LCS), n—a solution with
from the source beam is isolated by the monochromator and
the certified concentration(s) of the analytes.
measured by the photodetector. The amount of light absorbed
3.2.8 monochromator, n—a device used for isolating a
by the analyte is quantified by comparing the light transmitted
narrowportionofthespectrumbymeansofagratingorprism.
through the flame during nebulization of a known concentra-
3.2.9 nebulizer, n—in atomic absorption, the burner-system
tion of the analyte to light transmitted during nebulization of a
portion where the sample solution is converted into fine mist.
solution that does not contain any measurable concentration of
3.2.10 optimum concentration range, n—a limited concen-
the analyte.
tration range, that may be extended downward with scale
4.2 An atomic absorption spectrophotometer may have a
expansion (used to measure very small concentrations) or
singleordoublebeamsystem.Theadvantagesofasinglebeam
upward by using a less sensitive wavelength or by rotating the
systemarethatthelampusedasalightsourcecanbeoperated
burner head.
at much lower currents than those used in a double beam
3.2.10.1 Discussion—The range varies with the characteris-
system, thereby minimizing the problem of line broadening.
ticconcentrationoftheinstrumentandtheoperatingconditions
This provides for increased sensitivity and longer lamp life.
employed.
The disadvantage of single beam instruments is that a longer
3.2.11 sensitivity, n—the analyte concentration (sometimes
warm-up time is required and there is no means of correcting
referredtoasthecharacteristicconcentration)thatproducesan
for changes in intensity of the light source without continually
absorbance of 0.0044 absorbance units (1% absorption) when
zeroing the instrument between measurements.
4,5,6
compared to the analytical blanks.
4.3 The thermal energy provided by the flame causes the
3.2.11.1 Discussion—The characteristic concentration var-
dissociationofmetallicelementsfromtheircompoundsandthe
reduction of the elements to the ground state. The richness or
leanness of the flame may have a bearing on sensitivity. The
Bennett,P.A.,andRothery,E., IntroducingAtomicAbsorptionAnalysis,Varian
Publication, Mulgrave, Australia, 1983.
variation in hydrocarbon content of the flame will have an
Price, W. J., Spectrochemical Analysis by Atomic Absorption, John Wiley &
effectonthenumberofatomsreducedtothegroundstate.The
Sons, New York, NY, 1983.
compounds of some elements, especially refractory elements
VanLoon, J. C., Analytical Atomic Absorption Spectroscopy—Selected
Methods, Academic Press, New York, NY, 1980. such as aluminum or molybdenum are highly resistant to
D4691 − 17
thermaldecompositionandthereforerequireahighertempera- appropriate continuum source are passed through the flame
ture flame than less refractory elements such as iron or copper. atomizer and alternately read. Narrow-band emission of the
This is the reason that the nitrous oxide-acetylene flame is primary source is affected by the scatter and background
required for these elements. absorptionfromthematrixaswellastheabsorptionoflightby
analyte atoms. The broadband emission of the continuum
4.4 The amount of light absorbed in the flame is propor-
sourceissignificantlyaffectedonlybythebackgroundabsorp-
tional to the concentration of the element in solution. The
tion. The effect of the background is virtually removed by
relationshipbetweenabsorptionandconcentrationisexpressed
taking a ratio of the energy of the two sources.
by Beer’s law:
6.1.2 Zeeman Correction—The Zeeman correction system
2abc
I 5 I 10 (2)
o
involves the use of an external magnetic field to split the
where: atomic spectral line. When the magnetic field is off, both
sampleandbackgroundaremeasured.Whenthemagneticfield
I = transmitted radiant power,
is applied, the absorption line is shifted and only the back-
I = incident radiant power,
o
ground absorption is measured. Background correction is
a = absorptivity,
b = sample path length, and performed by electronically comparing the field-off and field-
c = concentrationofabsorbingspecieswithinthepathofthe
on measurements, yielding an analyte only absorption re-
light beam, mg/L.
sponse.
6.1.3 Smith-Hieftje System—This system involves cycling
4.5 The atomic absorption spectrophotometer is calibrated
theatomiclinesourceathighcurrentsforbriefintervals.These
withstandardsolutionscontainingknownconcentrationsofthe
intervals cause nonexcited atoms of the source element to
element of interest.Acalibration curve is constructed for each
undergo the process of self-reversal by emitting light at
analytefromwhichtheconcentrationintheunknownsampleis
wavelengths other than those of the analyte. This light is
determined.
absorbed only by the background, so that interspersing periods
5. Significance and Use
of high- and low-source current permit correction of the
background.
5.1 Elemental constituents in water and wastewater need to
be identified to support effective water quality monitoring and
6.2 Chemical interference is the most frequently encoun-
control programs. Currently, one of the most widely used and
tered interference in atomic absorption spectrophotometry. A
practicalmeansformeasuringconcentrationsofelementsisby
chemical interference may prevent, enhance, or suppress the
atomic absorption spectrophotometry.
formation of ground state atoms in the flame. For example, in
5.2 The major advantage of atomic absorption over atomic the case of calcium determinations, the presence of phosphate
emission is the almost total lack of spectral interferences. In or sulfate can result in the formation of a salt that hinders
atomic emission, the specificity of the technique is almost
proper atomization of the solution when it is aspirated into an
totally dependent on monochromator resolution. In atomic air-acetylene flame.This decreases the number of free, ground
absorption, however, the detector sees only the narrow emis- state atoms in the flame, resulting in lowered absorbance
sion lines generated by the element of interest. values. This interference can be eliminated by use of a nitrous
oxide-acetyleneflame.Likewise,aluminumcancauseasimilar
6. Interferences
interference when measuring magnesium. The addition of
appropriate complexing agents to the sample solution is a
6.1 Background absorption is caused by the formation of
molecularspeciesfromthesamplematrixthatscatterorabsorb technique intended to reduce or eliminate chemical
interferences, and it may increase the sensitivity of the test
the light emitted by the hollow cathode or electrodeless
discharge line source. Without correction, this will cause the method.
analytical results to be erroneously high. If background cor-
6.3 Alkaliandalkalineearthmetals,GroupsIandII,suchas
rection is not available, a non-absorbing wavelength should be
sodium and potassium may undergo ionization in the air-
checkedorthematrixofthestandardsandblankmatchedwith
acetylene and nitrous oxide-acetylene flames resulting in a
the sample constituents. Background correction is usually not
decrease in ground state atoms available for measurement by
necessary unless the solids concentration of the sample is very
atomic absorption. In the presence of an excess of an easily
high (>1%), or the analysis is being carried out at very short
ionizablealkalielementsuchascesium,however,ionizationof
wavelengths (<210 nm), or both. Preferably high solids type
thealkalielementwilloccurfirstandmayminimizeionization
samples should be extracted. Three approaches exist for
of the element of interest.
simultaneous background correction: continuum source,
Zeeman, and Smith-Hieftje. There are different benefits for 6.4 Ifasamplecontaininglowconcentrationsoftheelement
each of these background correction methods. The analyst being measured is analyzed immediately after a sample con-
shouldconsultthemanufacturer’sliteratureforapplicabilityto taining high concentrations, sample carryover may sometimes
analytical requirements. occur resulting in elevated readings. High concentrations are
6.1.1 Continuum Source—The continuum source proce- evidencedbymarkedflamecoloration,aconcentrationreading
duresinvolvetheuseofahydrogenordeuteriumarcsourcefor higher than that of the highest standard, or, a large fluctuation
the ultraviolet or a tungsten halide lamp for the visible region in the energy gage, or all of these conditions. To prevent this
ofthespectrum.Lightfromtheprimaryspectralsourceandthe typeofsampleinterference,routineaspirationofreagentwater
D4691 − 17
for about 15 s or more between samples is recommended, be used provided it is first ascertained that the water is of
depending on the concentration of element in the last sample sufficiently high purity to permit its use without adversely
analyzed. Complete purging of the system is ascertained by affecting the precision and bias of the test method.
aspiratingwateruntiltheabsorbancereadoutreturnstonearthe
8.3 Fuel, Acetylene (C H )—Minimum acceptable acety-
2 2
baseline.
lene purity is 99.5 vol %. Normally the cylinder is changed
6.5 Thephysicalpropertiesofsolutionsbeingaspiratedwill
whenthepressurereaches517kPa(75psig)iftheacetyleneis
not only change the nebulization uptake rate but will, for a
packed in acetone. Some manufacturers recommend different
variety of reasons, have a significant effect on sensitivity.
pressures. The analyst should check with the manufacturer for
Organic solvents such as those used in extraction techniques,
instructions. Prepurified grades use a proprietary solvent and
will usually enhance sensitivity. Solutions with high dissolved
can be used to 206 kPa (30 psig) before replacement. The
solids will usually result in a reduction in sensitivity.
analyst should follow the manufacturer’s instructions for the
use of prepurified grades with proprietary solvents to prevent
7. Apparatus
damage to gas control systems. Avoid introducing these sol-
vents into the instrument or else abnormally high pulsating
7.1 AtomicAbsorption Spectrophotometer—Asingleordual
channel, single or double-beam instrument having a grating background noise and possible damage to the instrument’s
plumbing system may result. To prevent solvent carryover,
monochromator, photomultiplier detector adjustable spectral
bandwidth, wavelength range from 190 to 800 nm, and allow acetylene cylinders to equilibrate for at least 24 h before
use after moving.
provisions for interfacing with a strip chart recorder or a
suitable data system. Refer to Practice E863.
8.4 Fuel, Hydrogen (H )—For some elements industrial
7.2 Burner—The burner recommended by the manufacturer grade hydrogen may be selected to achieve the desired flame
ofthespectrophotometershouldbeused.Forcertainelements,
characteristics.
a nitrous oxide burner is required.
8.5 Oxidant (Air)—The source may be a compressor or
7.3 Hollow Cathode Lamps—Single-element lamps are rec-
commercially bottled gas. Condition the air by passing it
ommended. Multi-element lamps are available but have a
through a filter element to remove oil, water, and particles.
shorter lifespan, are less sensitive, require a higher operating
Refer to the manufacturer’s guidelines for minimum and
current, and increase the chances of spectral interferences.
maximum delivery pressures.
Electrode-less discharge lamps may also be used.
8.6 Oxidant, Nitrous Oxide (N O)—For certain elements,
7.4 Photomultiplier Tube—Awide spectral range (160–900
industrial or medical grade nitrous oxide may be required to
nm) multiplier phototube is recommended. Refer to Practice
achieve the necessary flame temperature.
E520.
8.7 Stock Standard Solutions—Stock standard solutions
7.5 Data Storage and Reduction Devices, Computer- and
may be purchased as certified solutions or prepared from the
Microprocessor-Controlled Devices, or Strip Chart Recorders
American Chemical Society reagent grade materials. Store the
shallbeutilizedforcollection,storage,reduction,andproblem
solutions in high density polyethylene, glass or TFE-
recognition (such as drift, incomplete atomization, changes in
fluorocarbon containers at room temperature. Solutions should
sensitivity, etc.). Strip chart recorders shall have a full scale
be labeled with the preparation and expiration dates. They
deflection time of 0.2 s or less to ensure accuracy.
should be inspected periodically for signs of deterioration.
8. Reagents and Materials NOTE1—Polypropylenemaybeusedforsamplecollectionandstorage.
However, studies published by at least one atomic absorption spectropho-
8.1 Purity of Reagents—Reagent grade or better chemicals
tometermanufacturerindicatesevereproblemswithmetaladsorptiononto
shall be used in all tests. Unless otherwise indicated, it is
the walls of polypropylene surfaces. The analyst should conduct loss
intended that all reagents conform to the specifications of the studies with time to determine if adsorption is a problem.
Committee onAnalytical Reagents of theAmerican Chemical
8.8 Filter Paper—Purchase suitable filter paper. Typically
Society where such specifications are available. However, in
the filter papers have a pore size of 0.45-µm membrane.
some cases, these reagents may not be of sufficient purity due
Material such as fine-textured, acid-washed, ashless paper, or
tothesensitivityofthetechnique.Itistheresponsibilityofthe
glass fiber paper are acceptable. The user must first ascertain
usertoverifythatthepurityofreagentsusedforthistechnique
that the filter paper is of sufficient purity to use without
is sufficient.
adversely affecting the bias and precision of the test method.
8.2 Purity of Water—Unless otherwise indicated, reference
towatershallbeunderstoodtomeanreagentwaterconforming
9. Safety Precautions
to Specification D1193,Type I. Other reagent water types may
9.1 The majority of calibration standards and sample types
en
...

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: D4691 − 11 D4691 − 17
Standard Practice for
Measuring Elements in Water by Flame Atomic Absorption
Spectrophotometry
This standard is issued under the fixed designation D4691; 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 covers general considerations for the quantitative determination of elements in water and waste water by flame
atomic absorption spectrophotometry. Flame atomic absorption spectrophotometry is simple, rapid, and applicable to a large
number of elements in drinking water, surface waters, and domestic and industrial wastes. While some waters may be analyzed
directly, others will require pretreatment.
1.2 Detection limits, sensitivity, and optimum ranges of the elements will vary with the various makes and models of
satisfactory atomic absorption spectrometers. The actual concentration ranges measurable by direct aspiration are given in the
specific test method for each element of interest. In the majority of instances the concentration range may be extended lower by
use of electrothermal atomization and conversely extended upwards by using a less sensitive wavelength or rotating the burner
head. Detection limits by direct aspiration may also be extended through sample concentration, solvent extraction techniques, or
both. Where direct aspiration atomic absorption techniques do not provide adequate sensitivity, the analyst is referred to Practice
D3919 or specialized procedures such as the gaseous hydride method for arsenic (Test Methods D2972) and selenium (Test
Methods D3859), and the cold vapor technique for mercury (Test Method D3223).
1.3 Because of the differences among various makes and models of satisfactory instruments, no detailed operating instructions
can be provided. Instead the analyst should follow the instructions provided by the manufacturer of a particular instrument.
1.4 The values stated in either SI or inch-pound units are to be regarded as the standard. The values given in parentheses are
for information only.mathematical conversion to inch-pound units that are provided for information only and are not considered
standard.
1.5 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. For specific hazard statements see Section 9.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D2972 Test Methods for Arsenic in Water
D3223 Test Method for Total Mercury in Water
D3370 Practices for Sampling Water from Closed Conduits
D3859 Test Methods for Selenium in Water
D3919 Practice for Measuring Trace Elements in Water by Graphite Furnace Atomic Absorption Spectrophotometry
D4453 Practice for Handling of High Purity Water Samples
D5810 Guide for Spiking into Aqueous Samples
This practice is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved Sept. 1, 2011June 1, 2017. Published September 2011June 2017. Originally approved in 1987. Last previous edition approved in 20072011 as
D4691 – 02D4691 – 11.(2007). DOI: 10.1520/D4691-11.10.1520/D4691-17.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4691 − 17
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
E178 Practice for Dealing With Outlying Observations
E520 Practice for Describing Photomultiplier Detectors in Emission and Absorption Spectrometry
E863 Practice for Describing Atomic Absorption Spectrometric Equipment (Withdrawn 2004)
The last approved version of this historical standard is referenced on www.astm.org.
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3. Terminology
3.1 Definitions:
3.1.1 For definition of terms used in this practice, refer to Terminology D1129.
3.1 Definitions:
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 absorbance, n—the logarithm to the base 10 of the reciprocal of the transmittance ( T). A = log (1/T) = −log T.
10 10
3.2.2 absorptivity, n—the absorbance (A) divided by the product of the sample path length (b) and the concentration (c).
a = A/bc.
3.2.3 atomic absorption, n—the absorption of electromagnetic radiation by an atom resulting in the elevation of electrons from
their ground states to excited states.
3.2.3.1 Discussion—
Atomic-absorption spectrophotometry involves the measurement of light absorbed by atoms of interest as a function of the
concentration of those atoms in a particular solution.
3.2.4 continuing calibration blank, n—a solution containing no analytes (of interest) which is used to verify blank response and
freedom from carryover.
3.2.5 continuing calibration verification, n—a solution (or set of solutions) of known concentration used to verify freedom from
excessive instrumental drift; the concentration is to cover the range of calibration curve.
3.2.6 detection limit, n—in atomic absorption, is a function of the sensitivity and the signal–to–noise ratio in the analysis of a
specific element for a given set of parameters.
3.2.6.1 Discussion—
The instrument detection limit is determined statistically as some multiple, usually two or three times the standard deviation of the
signal-to-noise ratio.
3.2.7 laboratory control sample (LCS)—(LCS), n—a solution with the certified concentration(s) of the analytes.
3.2.8 monochromator, n—a device used for isolating a narrow portion of the spectrum by means of a grating or prism.
3.2.9 nebulizer, n—in atomic absorption, the burner-system portion where the sample solution is converted into fine mist.
3.2.10 optimum concentration range, n—a limited concentration range, that may be extended downward with scale expansion
(used to measure very small concentrations) or upward by using a less sensitive wavelength or by rotating the burner head.
3.2.10.1 Discussion—
The range varies with the characteristic concentration of the instrument and the operating conditions employed.
3.2.11 sensitivity, n—the analyte concentration (sometimes referred to as the characteristic concentration) that produces an
4,5,6
absorbance of 0.0044 absorbance units (1 % absorption) when compared to the analytical blanks.
Bennett, P. A., and Rothery, E., “Introducing Atomic Absorption Analysis,” Varian Publication, Mulgrave, Australia, 1983.Bennett, P. A., and Rothery, E., Introducing
Atomic Absorption Analysis, Varian Publication, Mulgrave, Australia, 1983.
Price, W. J., “Spectrochemical Analysis by Atomic Absorption,” John Wiley & Sons, New York, NY, 1983.Price, W. J., Spectrochemical Analysis by Atomic Absorption,
John Wiley & Sons, New York, NY, 1983.
VanLoon, J. C., “Analytical Atomic Absorption Spectroscopy—Selected Methods,” Academic Press, New York, NY, 1980.VanLoon, J. C., Analytical Atomic Absorption
Spectroscopy—Selected Methods, Academic Press, New York, NY, 1980.
3.2.11.1 Discussion—
The characteristic concentration varies with instrumental conditions and atomization efficiency, as well as other factors and should
be determined as conditions change. The characteristic concentration is determined by the following equation:
characteristic concentration 5 C 30.0044/A (1)
where:
C = concentration of the analyte, and
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A = absorbance of analyte concentration used in the determination.
The characteristic concentration defines the slope of the calibration curve.
3.2.12 spectral bandwidth, n—the observed dispersion between absorption bands.
3.2.12.1 Discussion—
This bandwidth is expressed as the exit slit multiplied by the observed separation of two emission lines divided by the difference
in wavelength between these lines.
3.2.13 spectrophotometer, n—an instrument that provides the ratio, or a function of the ratio, of the radiant power of a beam
as a function of spectral wavelength.
4. Summary of Practice
4.1 In flame atomic absorption spectrophotometry, a standard or sample solution is aspirated as a fine mist into a flame where
it is converted to an atomic vapor consisting of ground state atoms. The flame provides energy to the ground state atoms allowing
them to absorb electromagnetic radiation from a series of very narrow, sharply defined wavelengths. Light (from a hollow cathode
lamp or other source) consisting of the characteristic monochromatic radiation generated by excitation of the element of interest
is passed through the flame. Light from the source beam is isolated by the monochromator and measured by the photodetector. The
amount of light absorbed by the analyte is quantified by comparing the light transmitted through the flame during nebulization of
a known concentration of the analyte to light transmitted during nebulization of a solution that does not contain any measurable
concentration of the analyte.
4.2 An atomic absorption spectrophotometer may have a single or double beam system. The advantages of a single beam system
are that the lamp used as a light source can be operated at much lower currents than those used in a double beam system, thereby
minimizing the problem of line broadening. This provides for increased sensitivity and longer lamp life. The disadvantage of single
beam instruments is that a longer warm-up time is required and there is no means of correcting for changes in intensity of the light
source without continually zeroing the instrument between measurements.
4.3 The thermal energy provided by the flame causes the dissociation of metallic elements from their compounds and the
reduction of the elements to the ground state. The richness or leanness of the flame may have a bearing on sensitivity. The variation
in hydrocarbon content of the flame will have an effect on the number of atoms reduced to the ground state. The compounds of
some elements, especially refractory elements such as aluminum or molybdenum are highly resistant to thermal decomposition and
therefore require a higher temperature flame than less refractory elements such as iron or copper. This is the reason that the nitrous
oxide-acetylene flame is required for these elements.
4.4 The amount of light absorbed in the flame is proportional to the concentration of the element in solution. The relationship
between absorption and concentration is expressed by Beer’s law:
2abc
I 5 I 10 (2)
o
where:
I = transmitted radiant power,
I = incident radiant power,
o
a = absorptivity,
b = sample path length, and
c = concentration of absorbing species within the path of the light beam, mg/L.
4.5 The atomic absorption spectrophotometer is calibrated with standard solutions containing known concentrations of the
element of interest. A calibration curve is constructed for each analyte from which the concentration in the unknown sample is
determined.
5. Significance and Use
5.1 Elemental constituents in water and wastewater need to be identified to support effective water quality monitoring and
control programs. Currently, one of the most widely used and practical means for measuring concentrations of elements is by
atomic absorption spectrophotometry.
5.2 The major advantage of atomic absorption over atomic emission is the almost total lack of spectral interferences. In atomic
emission, the specificity of the technique is almost totally dependent on monochromator resolution. In atomic absorption, however,
the detector sees only the narrow emission lines generated by the element of interest.
6. Interferences
6.1 Background absorption is caused by the formation of molecular species from the sample matrix that scatter or absorb the
light emitted by the hollow cathode or electrodeless discharge line source. Without correction, this will cause the analytical results
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to be erroneously high. If background correction is not available, a non-absorbing wavelength should be checked or the matrix of
the standards and blank matched with the sample constituents. Background correction is usually not necessary unless the solids
concentration of the sample is very high (>1 %), or the analysis is being carried out at very short wavelengths (<210 nm), or both.
Preferably high solids type samples should be extracted. Three approaches exist for simultaneous background correction:
continuum source, Zeeman, and Smith-Hieftje. There are different benefits for each of these background correction methods. The
analyst should consult the manufacturer’s literature for applicability to analytical requirements.
6.1.1 Continuum Source—The continuum source procedures involve the use of a hydrogen or deuterium arc source for the
ultraviolet or a tungsten halide lamp for the visible region of the spectrum. Light from the primary spectral source and the
appropriate continuum source are passed through the flame atomizer and alternately read. Narrow-band emission of the primary
source is affected by the scatter and background absorption from the matrix as well as the absorption of light by analyte atoms.
The broadband emission of the continuum source is significantly affected only by the background absorption. The effect of the
background is virtually removed by taking a ratio of the energy of the two sources.
6.1.2 Zeeman Correction—The Zeeman correction system involves the use of an external magnetic field to split the atomic
spectral line. When the magnetic field is off, both sample and background are measured. When the magnetic field is applied, the
absorption line is shifted and only the background absorption is measured. Background correction is performed by electronically
comparing the field-off and field-on measurements, yielding an analyte only absorption response.
6.1.3 Smith-Hieftje System—This system involves cycling the atomic line source at high currents for brief intervals. These
intervals cause nonexcited atoms of the source element to undergo the process of self-reversal by emitting light at wavelengths
other than those of the analyte. This light is absorbed only by the background, so that interspersing periods of high- and low-source
current permit correction of the background.
6.2 Chemical interference is the most frequently encountered interference in atomic absorption spectrophotometry. A chemical
interference may prevent, enhance, or suppress the formation of ground state atoms in the flame. For example, in the case of
calcium determinations, the presence of phosphate or sulfate can result in the formation of a salt that hinders proper atomization
of the solution when it is aspirated into an air-acetylene flame. This decreases the number of free, ground state atoms in the flame,
resulting in lowered absorbance values. This interference can be eliminated by use of a nitrous oxide-acetylene flame. Likewise,
aluminum can cause a similar interference when measuring magnesium. The addition of appropriate complexing agents to the
sample solution is a technique intended to reduce or eliminate chemical interferences, and it may increase the sensitivity of the
test method.
6.3 Alkali and alkaline earth metals, Groups I and II, such as sodium and potassium may undergo ionization in the air-acetylene
and nitrous oxide-acetylene flames resulting in a decrease in ground state atoms available for measurement by atomic absorption.
In the presence of an excess of an easily ionizable alkali element such as cesium, however, ionization of the alkali element will
occur first and may minimize ionization of the element of interest.
6.4 If a sample containing low concentrations of the element being measured is analyzed immediately after a sample containing
high concentrations, sample carryover may sometimes occur resulting in elevated readings. High concentrations are evidenced by
marked flame coloration, a concentration reading higher than that of the highest standard, or, a large fluctuation in the energy gage,
or all of these conditions. To prevent this type of sample interference, routine aspiration of reagent water for about 15 s or more
between samples is recommended, depending on the concentration of element in the last sample analyzed. Complete purging of
the system is ascertained by aspirating water until the absorbance readout returns to near the baseline.
6.5 The physical properties of solutions being aspirated will not only change the nebulization uptake rate but will, for a variety
of reasons, have a significant effect on sensitivity. Organic solvents such as those used in extraction techniques, will usually
enhance sensitivity. Solutions with high dissolved solids will usually result in a reduction in sensitivity.
7. Apparatus
7.1 Atomic Absorption Spectrophotometer—A single or dual channel, single or double-beam instrument having a grating
monochromator, photomultiplier detector adjustable spectral bandwidth, wavelength range from 190 to 800 nm, and provisions for
interfacing with a strip chart recorder or a suitable data system. Refer to Practice E863.
7.2 Burner—The burner recommended by the manufacturer of the spectrophotometer should be used. For certain elements, a
nitrous oxide burner is required.
7.3 Hollow Cathode Lamps—Single-element lamps are recommended. Multi-element lamps are available but have a shorter
lifespan, are less sensitive, require a higher operating current, and increase the chances of spectral interferences. Electrode-less
discharge lamps may also be used.
7.4 Photomultiplier Tube—A wide spectral range (160–900 nm) multiplier phototube is recommended. Refer to Practice E520.
7.5 Strip Chart Recorder—Data Storage and Reduction Devices, Computer- and Microprocessor-Controlled Devices, or Strip
Chart Recorders A recorder is recommended so that there will be a permanent record and any problems with the analysis such shall
be utilized for collection, storage, reduction, and problem recognition (such as drift, incomplete atomization, changes in sensitivity,
etc., can be easily recognized.etc.). Strip chart recorders shall have a full scale deflection time of 0.2 s or less to ensure accuracy.
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8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade or better chemicals shall be used in all tests. Unless otherwise indicated, it is intended
that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where
such specifications are available. However, in some cases, these reagents may not be of sufficient purity due to the sensitivity of
the technique. It is the responsibility of the user to verify that the purity of reagents used for this technique is sufficient.
8.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to
Specification D1193, Type I. Other reagent water types may be used provided it is first ascertained that the water is of sufficiently
high purity to permit its use without adversely affecting the precision and bias of the test method.
8.3 Fuel, Acetylene (C H )—Minimum acceptable acetylene purity is 99.5 vol %. Normally the cylinder is changed when the
2 2
pressure reaches 53 g/m517 kPa (75 psig) if the acetylene is packed in acetone. Some manufacturers recommend different
pressures. The analyst should check with the manufacturer for instructions. Prepurified grades use a proprietary solvent and can
be used to 25–21 g/m206 kPa (30 psig) before replacement. The analyst should follow the manufacturer’s instructions for the use
of prepurified grades with proprietary solvents to prevent damage to gas control systems. Avoid introducing these solvents into the
instrument or else abnormally high pulsating background noise and possible damage to the instrument’s plumbing system may
result. To prevent solvent carryover, allow acetylene cylinders to equilibrate for at least 24 h before use after moving.
8.4 Fuel, Hydrogen (H )—For some elements industrial grade hydrogen may be selected to achieve the desired flame
characteristics.
8.5 Oxidant (Air)—The source may be a compressor or commercially bottled gas. Condition the air by passing it through a filter
element to remove oil, water, and particles. Refer to the manufacturer’s guidelines for minimum and maximum delivery pressures.
8.6 Oxidant, Nitrous Oxide (N O)—For certain elements, industrial or medical grade nitrous oxide may be required to achieve
the necessary flame temperature.
8.7 Stock Standard Solutions—Stock standard solutions may be purchased as certified solutions or prepared from the American
Chemical Society reagent grade materials. Store the solutions in high density polyethylene, glass or TFE-fluorocarbon containers
at room temperature. Solutions should be labeled with the preparation and expiration dates. They should be inspected periodically
for signs of deterioration.
NOTE 1—Polypropylene may be used for sample collection and storage. However, studies published by at least one atomic absorption
spectrophotometer manufacturer indicate severe problems with metal adsorption onto the walls of polypropylene surfaces. The analyst should conduct
loss studies with time to determine if adsorption is a problem.
8.8 Filter Paper—Purchase suitable filter paper. Typically the filter papers have a pore size of 0.45-μm membrane. Material such
as fine-textured, acid-washed, ashless paper, or glass fiber paper are acceptable. The user must first ascertain that the filter paper
is of sufficient purity to use without adversely affecting the bias and precision of the test method.
9. Safety Precautions
9.1 The majority of calibration standards and sample types encountered in this practice pose no hazard to the analyst. Use of
a hood, protective clothing, and safety glasses are required when preparing solutions where reaction between solvent and solute
is exothermic, that is, lanthanum oxide in acid solution. The same precautions are required when di
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