1、Designation: D4691 11Standard Practice forMeasuring Elements in Water by Flame Atomic AbsorptionSpectrophotometry1This standard is issued under the fixed designation D4691; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o
2、f last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers general considerations for thequantitative determination of elements in water and wastewater b
3、y 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 requirepretreatment.1.2 Det
4、ection 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 interest. In themajority
5、 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, solventextraction te
6、chniques, or both. Where direct aspiration atomicabsorption techniques do not provide adequate sensitivity, theanalyst is referred to Practice D3919 or specialized proceduressuch as the gaseous hydride method for arsenic (Test MethodsD2972) and selenium (Test Methods D3859), and the coldvapor techni
7、que for mercury (Test Method D3223).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 particularinstrument.1.4 The values s
8、tated in either SI or inch-pound units are tobe regarded as the standard. The values given in parenthesesare for information only.1.5 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 establis
9、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements see Section 9.2. Referenced Documents2.1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2972 Test Methods for Ar
10、senic in WaterD3223 Test Method for Total Mercury in WaterD3370 Practices for Sampling Water from Closed ConduitsD3859 Test Methods for Selenium in WaterD3919 Practice for Measuring Trace Elements in Water byGraphite Furnace Atomic Absorption SpectrophotometryD4453 Practice for Handling of High Puri
11、ty Water SamplesD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisE178 Practice for Dealing With Outlying ObservationsE520 Practice for Describing Photomultiplier Detectors inEmission and Absorption Spectr
12、ometryE863 Practice for Describing Atomic Absorption Spectro-metric Equipment33. Terminology3.1 Definitions:3.1.1 For definition of terms used in this practice, refer toTerminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 absorbance, nthe logarithm to the base 10 of thereciproc
13、al of the transmittance (T). A = log10(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
14、 from their ground states to excited states.1This 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 Sept. 1, 2011. Published September 2011. Originallyapproved in 1987. L
15、ast previous edition approved in 2007 as D4691 02(2007).DOI: 10.1520/D4691-11.2For 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 on
16、the ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1*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.3.2.3.1
17、 DiscussionAtomic-absorption spectrophotometryinvolves the measurement of light absorbed by atoms ofinterest as a function of the concentration of those atoms in aparticular solution.3.2.4 detection limit, nin atomic absorption is a functionof the sensitivity and the signaltonoise ratio in the analy
18、sis ofa specific element for a given set of parameters.3.2.4.1 DiscussionThe instrument detection limit is deter-mined statistically as some multiple, usually two or three timesthe standard deviation of the signal-to-noise ratio.3.2.5 laboratory control sample (LCS)a solution with thecertified conce
19、ntration(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, nin atomic absorption, the burner-systemportion where the sample solution is converted into fine mist.3.2.8 optimum concentration range, na li
20、mited concen-tration range, that may be extended downward with scaleexpansion (used to measure very small concentrations) orupward by using a less sensitive wavelength or by rotating theburner head.3.2.8.1 DiscussionThe range varies with the characteristicconcentration of the instrument and the oper
21、ating conditionsemployed.3.2.9 sensitivity, nthe analyte concentration (sometimesreferred to as the characteristic concentration) that produces anabsorbance of 0.0044 absorbance units (1 % absorption) whencompared to the analytical blanks.4,5,63.2.9.1 DiscussionThe characteristic concentration varie
22、swith instrumental conditions and atomization efficiency, aswell as other factors and should be determined as conditionschange. The characteristic concentration is determined by thefollowing equation:characteristic concentration 5 C 3 0.0044/A(1)where:C = concentration of the analyte andA = absorban
23、ce of analyte concentration used in the deter-mination.The characteristic concentration defines the slope of the calibrationcurve.3.2.10 spectral bandwidth, nthe observed dispersion be-tween absorption bands.3.2.10.1 DiscussionThis bandwidth is expressed as theexit slit multiplied by the observed se
24、paration of two emissionlines divided by the difference in wavelength between theselines.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 absorptio
25、n spectrophotometry, a stan-dard or sample solution is aspirated as 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, shar
26、ply defined wavelengths. Light(from a hollow cathode lamp or other 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 photodetecto
27、r. The amount of light absorbedby the analyte is quantified by comparing 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 a
28、tomic absorption spectrophotometer may have asingle or double beam 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 i
29、ncreased sensitivity and longer lamp life.The disadvantage of single 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 provide
30、d by the flame causes thedissociation of metallic elements from their 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 red
31、uced to the ground state. Thecompounds of some elements, especially 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 nitrou
32、s oxide-acetylene flame isrequired for these elements.4.4 The amount 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= i
33、ncident radiant power,a = absorptivity,b = sample path length, andc = 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 cu
34、rve is constructed for eachanalyte from which the concentration in the unknown sample isdetermined.4Bennett, P. A., and Rothery, E., “Introducing Atomic Absorption Analysis,”Varian Publication, Mulgrave, Australia, 1983.5Price, W. J., “Spectrochemical Analysis by Atomic Absorption,” John Wiley flame
35、D4691 116SUMMARY OF CHANGESCommittee D19 has identified the location of selected changes to this standard since the last issue(D4691 02(2007) that may impact the use of this standard.(1) The SI statement was added to Section 1.(2) D1192 was removed from Section 2 and 10.2.(3) Updated Terminology sec
36、tion.ASTM 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 advised that determination of the validity of any such patent rights, and the riskof infringement of such rights
37、, 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 reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional st
38、andardsand 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 you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Co
39、mmittee 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D4691 117
