ASTM D4691-02(2007)
(Practice)Standard Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry
Standard Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry
SIGNIFICANCE AND USE
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.
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 D 3919 or specialized procedures such as the gaseous hydride method for arsenic (Test Methods D 2972) and selenium (Test Methods D 3859), and the cold vapor technique for mercury (Test Method D 3223).
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.
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.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D4691–02 (Reapproved 2007)
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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers general considerations for the
quantitative determination of elements in water and waste D1129 Terminology Relating to Water
water by flame atomic absorption spectrophotometry. Flame D1192 GuideforEquipmentforSamplingWaterandSteam
atomic absorption spectrophotometry is simple, rapid, and in Closed Conduits
applicable to a large number of elements in drinking water, D1193 Specification for Reagent Water
surface waters, and domestic and industrial wastes. While D2972 Test Methods for Arsenic in Water
some waters may be analyzed directly, others will require D3223 Test Method for Total Mercury in Water
pretreatment. D3370 Practices for SamplingWater from Closed Conduits
1.2 Detection limits, sensitivity, and optimum ranges of the D3859 Test Methods for Selenium in Water
elements will vary with the various makes and models of D3919 Practice for Measuring Trace Elements in Water by
satisfactory atomic absorption spectrometers. The actual con- Graphite Furnace Atomic Absorption Spectrophotometry
centration ranges measurable by direct aspiration are given in D4453 Practice for Handling of Ultra-Pure Water Samples
the specific test method for each element of interest. In the D5810 Guide for Spiking into Aqueous Samples
majority of instances the concentration range may be extended D5847 Practice for Writing Quality Control Specifications
lower by use of electrothermal atomization and conversely for Standard Test Methods for Water Analysis
extended upwards by using a less sensitive wavelength or E178 Practice for Dealing With Outlying Observations
rotating the burner head. Detection limits by direct aspiration E520 Practice for Describing Photomultiplier Detectors in
may also be extended through sample concentration, solvent Emission and Absorption Spectrometry
extraction techniques, or both. Where direct aspiration atomic E863 Practice for Describing Atomic Absorption Spectro-
absorption techniques do not provide adequate sensitivity, the metric Equipment
analyst is referred to Practice D3919 or specialized procedures
3. Terminology
such as the gaseous hydride method for arsenic (Test Methods
3.1 Definitions:
D2972) and selenium (Test Methods D3859), and the cold
vapor technique for mercury (Test Method D3223). 3.1.1 For definition of terms used in this practice, refer to
Terminology D1129.
1.3 Because of the differences among various makes and
models of satisfactory instruments, no detailed operating in- 3.2 Definitions of Terms Specific to This Standard:
3.2.1 absorbance, n—the logarithm to the base 10 of the
structions can be provided. Instead the analyst should follow
the instructions provided by the manufacturer of a particular reciprocal of the transmittance (T). A=log (1/T)=−log T.
10 10
3.2.2 absorptivity, n—the absorbance (A) divided by the
instrument.
1.4 This standard does not purport to address all of the productofthesamplepathlength(b)andtheconcentration(c).
a= A/bc.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.2.3 atomic absorption, n—the absorption of electromag-
netic radiation by an atom resulting in the elevation of
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.Forspecifichazard electrons from their ground states to excited states. Atomic
absorption spectrophotometry involves the measurement of
statements see Section 9.
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 service@astm.org. For Annual Book of ASTM
Water. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 15, 2007. Published June 2007. Originally the ASTM website.
approved in 1987. Last previous edition approved in 2002 as D4691–02. DOI: Withdrawn. The last approved version of this historical standard is referenced
10.1520/D4691-02R07. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4691–02 (2007)
light absorbed by atoms of interest as a function of the characteristicmonochromaticradiationgeneratedbyexcitation
concentration of those atoms in a particular solution. of the element of interest is passed through the flame. Light
3.2.4 detection limit, n—afunctionofthesensitivityandthe from the source beam is isolated by the monochromator and
signal to noise ratio in the analysis of a specific element for a measured by the photodetector. The amount of light absorbed
given set of parameters. The detection limit is determined by the analyte is quantified by comparing the light transmitted
statistically as some multiple, usually two or three times the through the flame during nebulization of a known concentra-
standard deviation of the signal to noise ratio. tion of the analyte to light transmitted during nebulization of a
3.2.5 laboratory control sample (LCS)—a solution with the solution that does not contain any measurable concentration of
certified concentration(s) of the analytes. the analyte.
3.2.6 monochromator, n—a device used for isolating a 4.2 An atomic absorption spectrophotometer may have a
narrowportionofthespectrumbymeansofagratingorprism. singleordoublebeamsystem.Theadvantagesofasinglebeam
3.2.7 nebulizer, n—as used in atomic absorption, that systemarethatthelampusedasalightsourcecanbeoperated
portion of the burner system where the sample solution is at much lower currents than those used in a double beam
converted into fine mist. system, thereby minimizing the problem of line broadening.
3.2.8 optimum concentration range, n—defined by limits This provides for increased sensitivity and longer lamp life.
expressed in concentration, below which scale expansion must The disadvantage of single beam instruments is that a longer
be used and above which curve correction should be consid- warm-up time is required and there is no means of correcting
ered. The range varies with the characteristic concentration of for changes in intensity of the light source without continually
the instrument and the operating conditions employed. zeroing the instrument between measurements.
3.2.9 sensitivity, n—sometimes referred to as the character- 4.3 The thermal energy provided by the flame causes the
isticconcentration.Itisthatconcentrationoftheanalytewhich dissociationofmetallicelementsfromtheircompoundsandthe
produces an absorbance of 0.0044 absorbance units (1% reduction of the elements to the ground state. The richness or
4,5,6
absorption) when compared to the analytical blanks. The leanness of the flame may have a bearing on sensitivity. The
characteristic concentration varies with instrumental condi- variation in hydrocarbon content of the flame will have an
tions and atomization efficiency, as well as other factors and effectonthenumberofatomsreducedtothegroundstate.The
should be determined as conditions change. The characteristic compounds of some elements, especially refractory elements
concentration is determined by the following equation: such as aluminum or molybdenum are highly resistant to
thermaldecompositionandthereforerequireahighertempera-
characteristicconcentration 5 C 30.0044/A
ture flame than less refractory elements such as iron or copper.
(1)
This is the reason that the nitrous oxide-acetylene flame is
where:
required for these elements.
C = concentration of the analyte and
4.4 The amount of light absorbed in the flame is propor-
A = absorbance of analyte concentration used in the deter-
tional to the concentration of the element in solution. The
mination.
relationshipbetweenabsorptionandconcentrationisexpressed
The characteristic concentration defines the slope of the
by Beer’s law:
calibration curve.
2abc
I 5 I 10 (2)
o
3.2.10 spectral bandwidth, n—related to the observed dis-
persion between absorption bands. It is expressed as the exit
where:
slitmultipliedbytheobservedseparationoftwoemissionlines
I = transmitted radiant power,
divided by the difference in wavelength between these lines.
I = incident radiant power,
o
3.2.11 spectrophotometer, n—an instrument that provides
a = absorptivity,
the ratio, or a function of the ratio, of the radiant power of a
b = sample path length, and
beam as a function of spectral wavelength. c = concentration of absorbing species within the path of
the light beam, mg/L.
4. Summary of Practice
4.5 The atomic absorption spectrophotometer is calibrated
withstandardsolutionscontainingknownconcentrationsofthe
4.1 In flame atomic absorption spectrophotometry, a stan-
dard or sample solution is aspirated as a fine mist into a flame element of interest.Acalibration curve is constructed for each
analytefromwhichtheconcentrationintheunknownsampleis
where it is converted to an atomic vapor consisting of ground
state atoms. The flame provides energy to the ground state determined.
atoms allowing them to absorb electromagnetic radiation from
5. Significance and Use
a series of very narrow, sharply defined wavelengths. Light
(fromahollowcathodelamporothersource)consistingofthe
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
practicalmeansformeasuringconcentrationsofelementsisby
Bennett, P. A., and Rothery, E., “Introducing Atomic Absorption Analysis,”
Varian Publication, Mulgrave, Australia, 1983.
atomic absorption spectrophotometry.
Price,W. J., “SpectrochemicalAnalysis byAtomicAbsorption,” JohnWiley &
5.2 The major advantage of atomic absorption over atomic
Sons, New York, NY, 1983.
emission is the almost total lack of spectral interferences. In
VanLoon,J.C.,“AnalyticalAtomicAbsorptionSpectroscopy—SelectedMeth-
ods,” Academic Press, New York, NY, 1980. atomic emission, the specificity of the technique is almost
D4691–02 (2007)
totally dependent on monochromator resolution. In atomic state atoms in the flame, resulting in lowered absorbance
absorption, however, the detector sees only the narrow emis- values. This interference can be eliminated by use of a nitrous
sion lines generated by the element of interest. oxide-acetyleneflame.Likewise,aluminumcancauseasimilar
interference when measuring magnesium. The addition of
6. Interferences
appropriate complexing agents to the sample solution is a
6.1 Background absorption is caused by the formation of
technique intended to reduce or eliminate chemical interfer-
molecularspeciesfromthesamplematrixthatscatterorabsorb
ences, and it may increase the sensitivity of the test method.
the light emitted by the hollow cathode or electrodeless
6.3 Alkaliandalkalineearthmetals,GroupsIandII,suchas
discharge line source. Without correction, this will cause the
sodium and potassium may undergo ionization in the air-
analytical results to be erroneously high. If background cor-
acetylene and nitrous oxide-acetylene flames resulting in a
rection is not available, a non-absorbing wavelength should be
decrease in ground state atoms available for measurement by
checkedorthematrixofthestandardsandblankmatchedwith
atomic absorption. In the presence of an excess of an easily
the sample constituents. Background correction is usually not
ionizablealkalielementsuchascesium,however,ionizationof
necessary unless the solids concentration of the sample is very
thealkalielementwilloccurfirstandmayminimizeionization
high (>1%), or the analysis is being carried out at very short
of the element of interest.
wavelengths (<210 nm), or both. Preferably high solids type
6.4 Ifasamplecontaininglowconcentrationsoftheelement
samples should be extracted. Three approaches exist for
being measured is analyzed immediately after a sample con-
simultaneous background correction: continuum source, Zee-
taining high concentrations, sample carryover may sometimes
man,andSmith-Hieftje.Therearedifferentbenefitsforeachof
occur resulting in elevated readings. High concentrations are
these background correction methods. The analyst should
evidencedbymarkedflamecoloration,aconcentrationreading
consult the manufacturer’s literature for applicability to ana-
higher than that of the highest standard, or, a large fluctuation
lytical requirements.
in the energy gage, or all of these conditions. To prevent this
6.1.1 Continuum Source—The continuum source proce-
typeofsampleinterference,routineaspirationofreagentwater
duresinvolvetheuseofahydrogenordeuteriumarcsourcefor
for about 15 s or more between samples is recommended,
the ultraviolet or a tungsten halide lamp for the visible region
depending on the concentration of element in the last sample
ofthespectrum.Lightfromtheprimaryspectralsourceandthe
analyzed. Complete purging of the system is ascertained by
appropriate continuum source are passed through the flame
aspiratingwateruntiltheabsorbancereadoutreturnstonearthe
atomizer and alternately read. Narrow-band emission of the
baseline.
primary source is affected by the scatter and background
6.5 Thephysicalpropertiesofsolutionsbeingaspiratedwill
absorptionfromthematrixaswellastheabsorptionoflightby
not only change the nebulization uptake rate but will, for a
analyte atoms. The broadband emission of the continuum
variety of reasons, have a significant effect on sensitivity.
sourceissignificantlyaffectedonlybythebackgroundabsorp-
Organic solvents such as those used in extraction techniques,
tion. The effect of the background is virtually removed by
will usually enhance sensitivity. Solutions with high dissolved
taking a ratio of the energy of the two sources.
solids will usually result in a reduction in sensitivity.
6.1.2 Zeeman Correction—The Zeeman correction system
involves the use of an external magnetic field to split the
7. Apparatus
atomic spectral line. When the magnetic field is off, both
sampleandbackgroundaremeasured.Whenthemagneticfield
7.1 Atomic Absorption Spectrophotometer—A single or
is applied, the absorption line is shifted and only the back-
dual channel, single or doubl
...
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