1、Designation: D3919 15Standard Practice forMeasuring Trace Elements in Water by Graphite FurnaceAtomic Absorption Spectrophotometry1This standard is issued under the fixed designation D3919; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the year of 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 the general considerations for thequantitative determination of trace element
3、s in water andwastewater by graphite furnace atomic absorption spectropho-tometry. Furnace atomizers are a most useful means of extend-ing detection limits; however, the practice should only be usedat concentration levels below the optimum range of directflame aspiration atomic absorption spectropho
4、tometry. Be-cause of differences between various makes and models ofsatisfactory instruments, no detailed operating instructions canbe provided for each instrument. Instead, the analyst shouldfollow the instructions provided by the manufacturer of aparticular instrument.1.2 Wavelengths, estimated de
5、tection limits, and optimumconcentration ranges are given in the individual methods.Ranges may be increased or decreased by varying the volumeof sample injected or the instrumental settings or by the use ofa secondary wavelength. Samples containing concentrationshigher than those given in the optimu
6、m range may be dilutedor analyzed by other techniques.1.3 This technique is generally not applicable to brines andseawater. Special techniques such as separation of the traceelements from the salt, careful temperature control throughramping techniques, or matrix modification may be useful forthese s
7、amples.1.4 The analyst is encouraged to consult the literature asprovided by the instrument manufacturer as well as varioustrade journals and scientific publications.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This s
8、tandard 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.2. Referenced Documents2.
9、1 ASTM Standards:2D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD4841 Practice for Estimation of Holding Time for
10、 WaterSamples Containing Organic and Inorganic ConstituentsD5673 Test Method for Elements in Water by InductivelyCoupled PlasmaMass SpectrometryD5810 Guide for Spiking into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminol
11、ogy3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 graphite furnace, nan electrothermal graphite de-vice capable of reaching the specified temperatures required bythe element being determined.3.2.2 plat
12、form or similar device, n a flat, grooved orungrooved piece of pyrolytic graphite (which is inserted in thegraphite tube) on which the sample is placed (1).34. Summary of Practice4.1 The element is determined by an atomic absorptionspectrophotometer used in conjunction with a graphite furnace.The pr
13、inciple is essentially the same as with direct flameaspiration atomic absorption except a furnace, rather than aflame, is used to atomize the sample. The elemental atoms to be1This practice is under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.0
14、5 on Inorganic Constituents inWater.Current edition approved Feb. 1, 2015. Published March 2015. Originallyapproved in 1980. Last previous edition approved in 2008 as D3919 08. DOI:10.1520/D3919-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service
15、at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.*A Summary of Changes section appears at the end of this standardCo
16、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1measured are placed in the beam of radiation by increasing thetemperature of the furnace, thereby causing the injected speci-men to be volatilized. Radiation from a given excited elementis
17、 passed through the vapor containing ground-state atoms ofthat element. The decrease in intensity of the transmittedradiation is a measure of the amount of the ground-stateelement in the vapor. A monochromator isolates the character-istic radiation from the hollow-cathode lamp and a photosen-sitive
18、device measures the attenuated transmitted radiation.4.2 Dissolved elements are determined on a filtered samplewith no pretreatment. See 9.5.4.3 Total recoverable elements are determined followingacid digestion and filtration. If suspended material is notpresent, this digestion and filtration may be
19、 omitted.5. Significance and Use5.1 Elemental constituents in potable water, receiving water,and wastewater need to be identified for support of effectivepollution control programs. Currently, one of the most sensitiveand practical means for measuring low concentrations of traceelements is by graphi
20、te furnace atomic absorption spectropho-tometry. ICP-MS may also be appropriate but at a higherinstrument cost. See Test Method D5673.6. Interferences6.1 Background absorption is caused by the formation ofmolecular species from the sample matrix that absorb or scatterthe light emitted by the hollow
21、cathode or electrodelessdischarge line source. Without correction, this will cause theanalytical results to be erroneously high. Three approachesexist for simultaneous background correction: continuumsource, Zeeman, and Smith-Hieftje.6.1.1 Continuum SourceThe continuum source procedureinvolves the u
22、se of a deuterium arc source for the ultraviolet ora tungsten halide lamp for the visible region of the spectrum.Light from the primary spectral source and the appropriatecontinuum source are alternately passed through the graphitefurnace. Narrow-band emission of the primary source isaffected by the
23、 scatter and background absorption from thematrix as well as the absorption of light by analyte atoms. Thebroadband emission of the continuum source is affected onlyby the background absorption. The effect of the background isremoved by taking a ratio of the energy of the two sources.6.1.2 Zeeman Co
24、rrectionThe Zeeman correction systeminvolves the use of an external magnetic field to split theatomic spectral line. When the magnetic field is off, bothsample and background are measured. When the magnetic fieldis applied, the absorption line is shifted and only the back-ground absorption is measur
25、ed. Background correction isperformed by electronically comparing the field-off and field-on measurements, yielding an analyte-only absorption re-sponse.6.1.3 Smith-Hieftje SystemThis system involves cyclingthe atomic line source at high currents for brief intervals. Theseintervals cause nonexcited
26、atoms of the source element toundergo the process of self-reversal by emitting light atwavelengths other than those of the analyte. This light isabsorbed only by the background, so that interspersing periodsof high and low source current permit correction of thebackground.6.2 Some types of interfere
27、nce problems encountered indirect aspiration atomic absorption spectrophotometry can beobserved with the furnace technique. Although quite rare,spectral interference may be encountered. When this occurs,the use of another wavelength is suggested. Additionally, thefurnace technique is subject to chem
28、ical and matrix interfer-ence and the composition of the sample matrix can have amajor effect on the analysis. Therefore, for each differentmatrix encountered, the possibility of these interferencesshould be considered.6.3 Gases generated in the furnace during the atomizationmay have molecular absor
29、ption bands encompassing the ana-lytical wavelength. When this occurs, either using backgroundcorrection or choosing an alternative wavelength outside theabsorption band should eliminate this interference. Nonspecificbroadband absorption interference can also be compensated bybackground correction.6
30、.4 Memory effects occur if, during atomization, all theanalyte is not volatilized and removed from the furnace. Thiscondition is dependent on several factors, such as the volatilityof the element and its chemical form, whether pyrolyticgraphite is used, the rate of atomization, and furnace design. I
31、fthis situation is detected through blank burns, the tube must becleaned by operating the furnace at full power for the requiredtime period at regular intervals in the analytical scheme.6.5 Interference from a smoke-producing sample matrix cansometimes be reduced by extending the charring time at ah
32、igher temperature. Also, some instruments utilize an ashingcycle in the presence of air. Take care, however, to prevent lossof analyte.6.6 Samples containing large amounts of organic materialshould be oxidized by conventional acid digestion prior tobeing placed in the furnace. In this way, broadband
33、 absorptionwill be minimized. The use of expendable-type laboratory wareshould be considered to limit contamination.6.7 Carbide formation, resulting from the chemical environ-ment of the furnace, has been observed with certain elementsthat form carbides at high temperatures. Barium, molybdenum,nicke
34、l, titanium, and vanadium may be cited as examples.When this takes place, the element will be released very slowlyfrom the carbide and longer atomization times may be requiredbefore the signal returns to baseline levels. This problem isgreatly reduced and sensitivity increases with the use ofpyrolyt
35、ically coated graphite.6.8 Ionization interferences have to date not been reportedwith furnace techniques.6.9 Contamination of the sample can be a major source oferror because of the extreme sensitivities achieved with thefurnace. Keep the sample preparation work area scrupulouslyclean (see 9.1). Cl
36、ean all glassware with dilute HNO3(1 + 1).Pipette tips have been known to be a source of contamination.If suspected, acid soak them with HNO3(1 + 1) and rinsethoroughly with water. The use of only high-quality pipette tipsD3919 152greatly reduces this problem. It is very important that specialattent
37、ion be given to reagent blanks in both the analysis and thecorrection of analytical results. Lastly, pyrolytic graphite,because of the production process and handling, can becomecontaminated. As many as five, to possibly ten, high-temperature burns may be required to clean the tube before use.6.10 O
38、xide formation is greatly reduced because atomiza-tion occurs in an inert atmosphere.6.11 Several investigators who have studied interferences inthe graphite furnace have concluded that nitrate is the preferredanion of the matrix. Therefore, nitric acid is preferable for anydigestion or solubilizati
39、on step. If the situation absolutelyrequires the use of another acid in addition to HNO3,orinplace of HNO3(for example, tin), use the minimum amount ofacid. This applies particularly to hydrochloric and perchloricacids, but also to sulfuric and phosphoric acids to a lesserextent.6.12 The tests as ou
40、tlined in 6.12.1 6.12.5 are recom-mended prior to reporting analytical data. These tests willprovide indication whether positive or negative interferenceeffects are operative in any way on the analyte elementsthereby distorting the accuracy of the reported values.6.12.1 Spiking VerificationWhen the
41、sample absorbance is40 % or less of the absorbance of the highest standard on thestandard curve, the amount of spike added to the sample shouldresult in a net increase equal to 50 % of the highest standardconcentration. The purpose of adding a large spike is todifferentiate between matrix interferen
42、ces and random errors.The recovery of the spike must be between 90 and 110 % forverification of the original determination. If the result of theoriginal determination is above 40 % on the curve, two aliquotsshould be withdrawn and diluted at least 1 + 1. One of thealiquots should be spiked before di
43、lution with an amountresulting in a net increase over the unspiked aliquot equivalentto 50 % of the highest standard concentration. The reportedresult should be based on the analysis of the diluted aliquot.For verification of this result, the spike recovery must bebetween 90 and 110 %. For spiking v
44、erification to be valid ineither situation in the presence of nonspecific absorbance,simultaneous background correction must be used duringanalysis. If the result of the determination cannot be verified,the sample should be treated in one or more of the followingways:6.12.2 Serial DilutionSuccessive
45、ly dilute and reanalyzethe sample using spiking verifications to determine if theinterference can be eliminated. This assumes that the analyteoccurs at a sufficiently high concentration.6.12.3 Matrix ModificationMatrix modifiers are fre-quently used to stabilize volatile or moderately volatile analy
46、temetals such as lead, cadmium, chromium, and nickel. Metalssuch as these begin to volatilize at very low temperatures andrequire that the charring/ashing temperature be lowered. Lowercharring/ashing temperatures reduce the chance of removingpotential interferents from the matrix during the charring
47、/ashing step. Adding certain chemical compounds or combina-tions of chemical compounds will reduce the volatility ofselected metals by the formation of less volatile compoundsduring the charring/ashing process. The use of ammoniumdihydrogen phosphate or phosphoric acid results in highervolatilizatio
48、n temperatures for many elements, thus permittingthe use of higher charring/ashing temperatures to remove orreduce matrix interferences. Nickel nitrate has been shown toperform the same role for arsenic and selenium by forminghigh temperature arsenides and selenides. An alternate ap-proach to the sa
49、me problem is to reduce the temperature atwhich the matrix volatilizes, permitting it to be removed at alower charring/ashing temperature. Sodium chloride in seawa-ter can be volatilized by adding ammonium nitrate as a matrixmodifier. The sodium nitrate and ammonium chloride formedare more volatile than the sodium chloride and can bevolatilized at much lower charring/ashing temperatures. Othermatrix modifiers include various organic acids such as citricand ascorbic acid. These acids are believed to reduce matrixinterferences by preventing the formation of large salt crys
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