1、Designation: D 4691 02 (Reapproved 2007)Standard Practice forMeasuring Elements in Water by Flame Atomic AbsorptionSpectrophotometry1This standard is issued under the fixed designation D 4691; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers general considerations for thequantitative determination of elements in wa
3、ter and wastewater by flame atomic absorption spectrophotometry. Flameatomic absorption spectrophotometry is simple, rapid, andapplicable to a large number of elements in drinking water,surface waters, and domestic and industrial wastes. Whilesome waters may be analyzed directly, others will require
4、pretreatment.1.2 Detection limits, sensitivity, and optimum ranges of theelements will vary with the various makes and models ofsatisfactory atomic absorption spectrometers. The actual con-centration ranges measurable by direct aspiration are given inthe specific test method for each element of inte
5、rest. In themajority of instances the concentration range may be extendedlower by use of electrothermal atomization and converselyextended upwards by using a less sensitive wavelength orrotating the burner head. Detection limits by direct aspirationmay also be extended through sample concentration,
6、solventextraction techniques, or both. Where direct aspiration atomicabsorption techniques do not provide adequate sensitivity, theanalyst is referred to Practice D 3919 or specialized proceduressuch as the gaseous hydride method for arsenic (Test MethodsD 2972) and selenium (Test Methods D 3859), a
7、nd the coldvapor technique for mercury (Test Method D 3223).1.3 Because of the differences among various makes andmodels of satisfactory instruments, no detailed operating in-structions can be provided. Instead the analyst should followthe instructions provided by the manufacturer of a particularins
8、trument.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For sp
9、ecific hazardstatements see Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1192 Guide for Equipment for Sampling Water andSteam in Closed Conduits3D 1193 Specification for Reagent WaterD 2972 Test Methods for Arsenic in WaterD 3223 Test Method for Total Me
10、rcury in WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3859 Test Methods for Selenium in WaterD 3919 Practice for Measuring Trace Elements in Water byGraphite Furnace Atomic Absorption SpectrophotometryD 4453 Practice for Handling of Ultra-Pure Water SamplesD 5810 Guide for Spiking
11、into Aqueous SamplesD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisE 178 Practice for Dealing With Outlying ObservationsE 520 Practice for Describing Photomultiplier Detectors inEmission and Absorption SpectrometryE 863 Practice for Describing A
12、tomic Absorption Spectro-metric Equipment33. Terminology3.1 Definitions:3.1.1 For definition of terms used in this practice, refer toTerminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 absorbance, nthe logarithm to the base 10 of thereciprocal of the transmittance (T). A = lo
13、g10(1/T) = log10T.3.2.2 absorptivity, nthe absorbance (A) divided by theproduct of the sample path length (b) and the concentration (c).a = A/bc.3.2.3 atomic absorption, nthe absorption of electromag-netic radiation by an atom resulting in the elevation ofelectrons from their ground states to excite
14、d states. Atomicabsorption spectrophotometry involves the measurement of1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.05 on Inorganic Constituents inWater.Current edition approved June 15, 2007. Published June 2007. Origin
15、allyapproved in 1987. Last previous edition approved in 2002 as D 4691 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe
16、ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.light absorbed by atoms of interest as a function of theconcentration of those atoms in a particular solution.3.2.4 detection limit, na function of the sensitivi
17、ty and thesignal to noise ratio in the analysis of a specific element for agiven set of parameters. The detection limit is determinedstatistically as some multiple, usually two or three times thestandard deviation of the signal to noise ratio.3.2.5 laboratory control sample (LCS)a solution with thec
18、ertified concentration(s) of the analytes.3.2.6 monochromator, na device used for isolating anarrow portion of the spectrum by means of a grating or prism.3.2.7 nebulizer, nas used in atomic absorption, thatportion of the burner system where the sample solution isconverted into fine mist.3.2.8 optim
19、um concentration range, ndefined by limitsexpressed in concentration, below which scale expansion mustbe used and above which curve correction should be consid-ered. The range varies with the characteristic concentration ofthe instrument and the operating conditions employed.3.2.9 sensitivity, nsome
20、times referred to as the character-istic concentration. It is that concentration of the analyte whichproduces an absorbance of 0.0044 absorbance units (1 %absorption) when compared to the analytical blanks.4,5,6Thecharacteristic concentration varies with instrumental condi-tions and atomization effi
21、ciency, as well as other factors andshould be determined as conditions change. The characteristicconcentration is determined by the following equation:characteristic concentration 5 C 3 0.0044/A(1)where:C = concentration of the analyte andA = absorbance of analyte concentration used in the deter-min
22、ation.The characteristic concentration defines the slope of thecalibration curve.3.2.10 spectral bandwidth, nrelated to the observed dis-persion between absorption bands. It is expressed as the exitslit multiplied by the observed separation of two emission linesdivided by the difference in wavelengt
23、h between these lines.3.2.11 spectrophotometer, nan instrument that providesthe ratio, or a function of the ratio, of the radiant power of abeam as a function of spectral wavelength.4. Summary of Practice4.1 In flame atomic absorption spectrophotometry, a stan-dard or sample solution is aspirated as
24、 a fine mist into a flamewhere it is converted to an atomic vapor consisting of groundstate atoms. The flame provides energy to the ground stateatoms allowing them to absorb electromagnetic radiation froma series of very narrow, sharply defined wavelengths. Light(from a hollow cathode lamp or other
25、source) consisting of thecharacteristic monochromatic radiation generated by excitationof the element of interest is passed through the flame. Lightfrom the source beam is isolated by the monochromator andmeasured by the photodetector. The amount of light absorbedby the analyte is quantified by comp
26、aring the light transmittedthrough the flame during nebulization of a known concentra-tion of the analyte to light transmitted during nebulization of asolution that does not contain any measurable concentration ofthe analyte.4.2 An atomic absorption spectrophotometer may have asingle or double beam
27、system.The advantages of a single beamsystem are that the lamp used as a light source can be operatedat much lower currents than those used in a double beamsystem, thereby minimizing the problem of line broadening.This provides for increased sensitivity and longer lamp life.The disadvantage of singl
28、e beam instruments is that a longerwarm-up time is required and there is no means of correctingfor changes in intensity of the light source without continuallyzeroing the instrument between measurements.4.3 The thermal energy provided by the flame causes thedissociation of metallic elements from the
29、ir compounds and thereduction of the elements to the ground state. The richness orleanness of the flame may have a bearing on sensitivity. Thevariation in hydrocarbon content of the flame will have aneffect on the number of atoms reduced to the ground state. Thecompounds of some elements, especially
30、 refractory elementssuch as aluminum or molybdenum are highly resistant tothermal decomposition and therefore require a higher tempera-ture flame than less refractory elements such as iron or copper.This is the reason that the nitrous oxide-acetylene flame isrequired for these elements.4.4 The amoun
31、t of light absorbed in the flame is propor-tional to the concentration of the element in solution. Therelationship between absorption and concentration is expressedby Beers law:I 5 Io102abc(2)where:I = transmitted radiant power,Io= incident radiant power,a = absorptivity,b = sample path length, andc
32、 = concentration of absorbing species within the path ofthe light beam, mg/L.4.5 The atomic absorption spectrophotometer is calibratedwith standard solutions containing known concentrations of theelement of interest. A calibration curve is constructed for eachanalyte from which the concentration in
33、the unknown sample isdetermined.5. Significance and Use5.1 Elemental constituents in water and wastewater need tobe identified to support effective water quality monitoring andcontrol programs. Currently, one of the most widely used andpractical means for measuring concentrations of elements is byat
34、omic absorption spectrophotometry.5.2 The major advantage of atomic absorption over atomicemission is the almost total lack of spectral interferences. Inatomic emission, the specificity of the technique is almost4Bennett, P. A., and Rothery, E., “Introducing Atomic Absorption Analysis,”Varian Public
35、ation, Mulgrave, Australia, 1983.5Price, W. J., “Spectrochemical Analysis by Atomic Absorption,” John Wiley flameASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advi
36、sed that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either
37、reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If
38、 you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 4691 02 (2007)6
