ASTM D2972-2008 Standard Test Methods for Arsenic in Water《水中砷含量的标准试验方法》.pdf

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1、Designation: D 2972 08Standard Test Methods forArsenic in Water1This standard is issued under the fixed designation D 2972; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicate

2、s the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods2cover the photometric and atomicabsorption determination of arsenic in most waters and waste-waters. Three test methods are given as follows:Conce

3、ntrationRangeSectionsTest Method ASilver Diethyldithio-carbamate Colorimetric5 to 250 g/L 7 to 15Test Method BAtomic Absorption,Hydride Generation1to20g/L 16to24Test Method CAtomic Absorption,Graphite Furnace5to100g/L 25to331.2 The analyst should direct attention to the precision andbias statements

4、for each test method. It is the users responsi-bility to ensure the validity of these test methods for waters ofuntested matrices.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address

5、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 specific hazardstatements, see Note 1 and Note 6.2. Refe

6、renced Documents2.1 ASTM Standards:3D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3919 Practice for Measuri

7、ng Trace Elements in Water byGraphite Furnace Atomic Absorption SpectrophotometryD 4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD 5810 Guide for Spiking into Aqueous SamplesD 5847 Practice for Writing Quality Control Specificationsfor Sta

8、ndard Test Methods for Water AnalysisE60 Practice for Analysis of Metals, Ores, and RelatedMaterials by Molecular Absorption SpectrometryE 275 Practice for Describing and Measuring Performanceof Ultraviolet, Visible, and Near-Infrared Spectrophotom-eters3. Terminology3.1 Definitions of Term Specific

9、 to This Standard:3.1.1 For definitions of terms used in these test methodsrefer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 total recoverable arsenican arbitrary analytical termrelating to the forms of arsenic that are determinable by thedigestion method which is

10、included in the procedure. Someorganic-arsenic compounds, such as phenylarsonic acid, diso-dium methane arsonate, and dimethylarsonic acid, are notrecovered completely during the digestion step.1These test methods are under the jurisdiction of ASTM Committee D19 onWater and are the direct responsibi

11、lity of Subcommittee D19.05 on InorganicConstituents in Water.Current edition approved Oct. 1, 2008. Published October 2008. Originallyapproved in 1993. Last previous edition approved in 2003 as D 2972 03.2Similar to that appearing in Standard Methods for the Examination of Waterand Wastewater, 12th

12、 edition, APHA, Inc., New York, NY, 1965, and identical withthat in Brown, Eugene, Skougstad, M. W., and Fishman, M. J., “Methods forCollection and Analysis of Water Samples for Dissolved Minerals and Gases,”Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book5, 1970 p. 4

13、6.3For 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 ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo

14、x C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 Herbicides, insecticides, and many industrial effluentscontain arsenic and are potential sources of water pollution.Arsenic is significant because of its adverse physiologicaleffects on humans.5. Purity of Reagents5.1

15、 Reagent grade chemicals shall be used in all tests.Unless otherwise indicated, it is intended that all reagents shallconform to the specifications of the Committee on AnalyticalReagents of the American Chemical Society, where suchspecifications are available.4Other grades may be used, pro-vided it

16、is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.5.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193 Type I. Other reagent

17、 water types maybe used provided it is first ascertained that the water is ofsufficiently high purity to permit its use without adverselyaffecting the bias and precision of the test method. Type IIwater was specified at the time of round robin testing of thistest method.6. Sampling6.1 Collect the sa

18、mple in accordance with Practices D 3370.6.2 Preserve the samples with HNO3(sp gr 1.42) to a pH of2 or less immediately at the time of collection; normally about2 mL/L is required. If only dissolved arsenic is to be deter-mined, filter the sample through a 0.45-m membrane filterbefore acidification.

19、 The holding times for the samples may becalculated in accordance with Practice D 4841.TEST METHOD ASILVERDIETHYLDITHIOCARBAMATE COLORIMETRIC7. Scope7.1 This test method covers the determination of dissolvedand total recoverable arsenic in most waters and waste watersin the range from 5 to 250 g/L o

20、f arsenic.7.2 The precision and bias data were obtained on reagentwater, river water, and process water. The information onprecision and bias may not apply to other waters. It is the usersresponsibility to ensure the validity of this test method forwaters of untested matrices.8. Summary of Test Meth

21、od8.1 Organic arsenic-containing compounds are decomposedby adding sulfuric and nitric acids and repeatedly evaporatingthe sample to fumes of sulfur trioxide. The arsenic (V) soproduced, together with inorganic arsenic originally present, issubsequently reduced to arsenic (III) by potassium iodide a

22、ndstannous chloride, and finally to gaseous arsine by zinc inhydrochloric acid solution. The resulting mixture of gases ispassed through a scrubber containing borosilicate wool im-pregnated with lead acetate solution and then into an absorp-tion tube containing a solution of silver diethyldithiocarb

23、amatein pyridine. Arsine reacts with this reagent to form a red-colored silver sol having maximum absorbance at about 540nm. The absorbance of the solution is measured photometri-cally and the arsenic determined by reference to an analyticalcurve prepared from standards.9. Interferences9.1 Although

24、many samples are relatively free of interfer-ences, several metals, notably cobalt, nickel, mercury, silver,platinum, copper, chromium, and molybdenum, may interferewith the evolution of arsine and with the recovery of arsenic.The presence of any or all of these metals in a sample beinganalyzed must

25、 be considered as a potential source of interfer-ence, and the analyst must fully determine the extent of actualinterference, if any. This could be accomplished by spiking.9.2 Hydrogen sulfide and other sulfides interfere, but com-monly encountered quantities are effectively removed by thelead aceta

26、te scrubber and the digestion.9.3 Antimony interferes by forming stibine, which distillsalong with the arsine. Stibine reacts with the color-formingreagent to form a somewhat similar red sol having maximum4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washing

27、ton, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD. FIG. 1 Arsi

28、ne Generator, Scrubber, and Absorber7D2972082absorbance near 510 nm. The sensitivity for antimony at 540nm is only about 8 % that of arsenic (1 mg/L of antimony willshow an apparent presence of 0.08 mg/L of arsenic).9.4 Nitric acid interferes with the test and must be com-pletely eliminated during t

29、he digestion.10. Apparatus10.1 Arsine Generator, Scrubber, and Absorber,5assembledas shown in Fig. 1.10.2 Spectrophotometer or Filter Photometer, suitable foruse at 540 nm and providing a light path of at least 10 mm. Thefilter photometer and photometric practice prescribed in thismethod shall confo

30、rm to Practice E60. The spectrophotometershall conform to Practice E 275.11. Reagents11.1 Arsenic Solution, Stock (1.00 mL = 1.00 mg As)Commercially purchase or dissolve 1.320 g of arsenic trioxide(As2O3)(Warning: see Note 1), dried for at least1hat110C,in 10 mL of NaOH solution (420 g/L) and dilute

31、 to 1 L withwater. This solution is stable.NOTE 1Warning: Arsenic trioxide is extremely toxic. Avoid inges-tion or inhalation of dry powder during standard preparation. Wash handsthoroughly immediately after handling arsenic trioxide. Under no circum-stances pipette any arsenic solutions by mouth.11

32、.2 Arsenic Solution, Intermediate (1.00 mL = 10.0 gAs) Dilute 5.00 mL of arsenic stock solution to 500 mL withwater.11.3 Arsenic Solution, Standard (1.00 mL = 1.00 g As)Dilute 10.0 mLof arsenic intermediate solution to 100 mLwithwater. Prepare fresh before each use.11.4 Hydrochloric Acid (sp gr 1.19

33、)Concentrated hydro-chloric acid (HCl). Use analytical grade acid with an arseniccontent not greater than 1 3 106%.11.5 Lead Acetate Solution (100 g/L)Dissolve 10 g oflead acetate (Pb(C2H3O2)23H2O) in 100 mL of water. Storereagent in a tightly stoppered container.11.6 Nitric Acid (sp gr 1.42)Concent

34、rated nitric acid(HNO3). Use analytical grade acid with an arsenic content notgreater than 1 3 106%.11.7 Nitric Acid (1 + 1)Add 250 mL of concentratednitric acid (sp gr 1.42) to 250 mL of water.11.8 Potassium Iodide Solution (150 g/L)Dissolve 15 g ofpotassium iodide (KI) in 100 mL of water. Store in

35、 an amberbottle.11.9 Silver Diethyldithiocarbamate SolutionDissolve 1 gof silver diethyldithiocarbamate (AgDDC) in 200 mL ofpyridine. This solution is stable for at least several monthswhen stored in an amber bottle.11.10 Sodium Hydroxide Solution (420 g/L)Dissolve 42 gof sodium hydroxide (NaOH) pel

36、lets in 100 mL of water.Warning: This is a very exothermic reaction.11.11 Stannous Chloride SolutionDissolve 40 g ofarsenic-free stannous chloride (SnCl22H2O) in 100 mLof HCl(sp gr 1.19). Add a few small pieces of mossy tin (which is thecommon name and is commercially available).11.12 Sulfuric Acid

37、(1 + 1)Cautiously, and with constantstirring and cooling, add 250 mL of concentrated H2SO4(sp gr1.84) to 250 mL of water.11.13 Zinc, Granular, 20-mesh. Arsenic content must notexceed 1 3 106%.12. Standardization12.1 Clean all glassware before use by rinsing first with hotHNO3(1 + 1) and then with wa

38、ter. The absorbers must beadditionally rinsed with acetone and then air-dried.12.2 Prepare, in a 250-mL generator flask, a blank andsufficient standards containing from 0.0 to 25.0 g of arsenicby diluting 0.0 to 25.0-mL portions of the arsenic standardsolution to approximately 100 mL with water.12.3

39、 Proceed as directed in 13.3-13.9.12.4 Construct an analytical curve by plotting the absor-bances of standards versus micrograms of arsenic.NOTE 2The response is linear up to 15 g of arsenic; however,because the curve is nonlinear above 15 g, it is necessary to havesufficient standards above 15 g to

40、 permit constructing an accurate curve.13. Procedure13.1 Clean all glassware before use by rinsing first with hotHNO3(1 + 1) and then with water. The absorbers must beadditionally rinsed with acetone and then air-dried.13.2 Pipette a volume of well-mixed acidified sample con-taining less than 25 g o

41、f arsenic (100 mL maximum) into agenerating flask and dilute to approximately 100 mL.NOTE 3If only dissolved arsenic is to be determined use a filtered andacidified sample (see 6.2).13.3 To each flask, add 7 mL of H2SO4(1+1)and5mLofconcentrated HNO3. Add a small boiling chip and carefullyevaporate t

42、o dense fumes of SO3, maintaining an excess ofHNO3until all organic matter is destroyed. This preventsdarkening of the solution and possible reduction and loss ofarsenic. Cool, add 25 mL of water, and again evaporate todense fumes of SO3. Maintain heating for 15 min to expeloxides of nitrogen.13.4 C

43、ool, and adjust the volume in each flask to approxi-mately 100 mL with water.13.5 To each flask add successively, with thorough mixingafter each addition, 8 mL of concentrated HCl, 4 mL of KIsolution, and 1 mL of SnCl2solution. Allow about 15 min forcomplete reduction of the arsenic to the trivalent

44、 state.13.6 Place in each scrubber a plug of borosilicate wool thathas been impregnated with lead acetate solution. Assemble thegenerator, scrubber, and absorber, making certain that all partsfit and are correctly adjusted. Add 3.00 mL of silverdiethyldithiocarbamate-pyridine solution to each absorb

45、er.Addglass beads to the absorbers until the liquid just covers them.NOTE 4Four millilitres of silver diethyldithiocarbamate-pyridine so-lution may be used with some loss of sensitivity.13.7 Disconnect each generator, add6gofzinc, andreconnect immediately.13.8 Allow 30 min for complete evolution of

46、arsine. Warmthe generator flasks for a few minutes to make sure that allarsine is released.5Available commercially.D297208313.9 Pour the solutions from the absorbers directly intoclean spectrophotometer cells and within 30 minutes measurethe absorbance of each at 540 nm.14. Calculation14.1 Determine

47、 the weight of arsenic in each sample byreferring to the analytical curve. Calculate the concentration ofarsenic in the sample in micrograms per litre, using Eq 1:Arsenic, g/L 5 1000 W/V (1)where:1000 = 1000 mL / LitreV = volume of sample, mL, andW = weight of arsenic in sample, g.15. Precision and

48、Bias615.1 The single-operator and overall precision of thismethod for three laboratories, which included a total of sixoperators analyzing each sample on three different days, withinits designated range varies with the quantity being tested inaccordance with Table 1.15.2 Recoveries of known amounts

49、of arsenic (arsenictrioxide) in a series of prepared standards are given in Table 1.15.3 The precision and bias data were obtained on reagentwater, river water, and process water. The information onprecision and bias may not apply to other waters. It is the usersresponsibility to ensure the validity of this test method forwaters of untested matrices.15.4 Three independent laboratories participated in theround robin study. Precision and bias for this test methodconform to Practice D 2777 77, which was in place at thetime of collaborative