ASTM D3372-2012 Standard Test Method for Molybdenum in Water《水中钼含量的标准试验方法》.pdf

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1、Designation: D3372 12Standard Test Method forMolybdenum in Water1This standard is issued under the fixed designation D3372; 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers the determination of dissolvedand total recoverable molybde

3、num in most waters,wastewaters, and brines by atomic absorption spectroscopy.21.2 This test method is applicable in the range from 1 to 25g/L of molybdenum. The range may be extended by dilutionof the sample.1.3 This test method has been used successfully with naturaland reagent waters. It is the us

4、ers responsibility to ensure thevalidity of this test method for waters of untested matrices.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system are mathematical conversions and may not beexact equivalents; therefore,

5、 each system shall be used inde-pendently of the other.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 establish appro-priate safety and health practices and determine the applica-bility

6、 of regulatory limitations prior to use. For specificprecautionary statements, see Note 3 and Note 11.2. Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of

7、 Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD4691 Practice for Measuring Elements in Water by FlameAtomic Absorption SpectrophotometryD4841 Practice for Estimation of Holding Time for WaterSamples Containing Organic and Inorganic ConstituentsD5810 Guide for Spiking

8、into Aqueous SamplesD5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water Analysis3. Terminology3.1 Definitions: For definitions of terms used in this testmethod, refer to Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 laboratory con

9、trol samplea solution with the certi-fied concentration(s) of the analytes.3.2.2 total recoverable molybdenuman arbitrary analyticalterm relating to the forms of molybdenum that are determin-able by the digestion procedure described in this test method.4. Summary of Test Method4.1 Molybdenum is dete

10、rmined by atomic-absorption spec-trophotometry. The element is chelated with8-hydroxyquinoline, extracted with methyl isobutyl ketone,and the extract aspirated into the nitrous oxide-acetylene flameof the spectrophotometer.5. Significance and Use5.1 Molybdenum can be found in waste that results from

11、chemical cleaning of components in which the metal is alloyed.5.2 National Pollution Discharge Elimination System(NPDES) permits or other standards, or both, require monitor-ing pollutants in waste discharged onto the water shed of, orinto, navigable waters, and those disposed of in such a mannertha

12、t eventual contamination of underground water could result.5.3 This test method affords an accurate and sensitive meansof determining compliance with those permits.6. Interferences6.1 Vanadium (V) and iron (III) enhance the absorption,while chromium (VI) and tungsten (VI) suppress it. Theseinterfere

13、nces are eliminated by the addition of ascorbic acid.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Sept. 1, 2012. Published October 2012. Originallyapproved

14、in 1975. Last previous edition approved in 2002 as D3372 02(2007)E01.DOI: 10.1520/D3372-12.2Chau, Y. K., and Lum-Shue-Chan, K., “Atomic Absorption Determination ofMicrogram Quantities of Molybdenum in Lake Waters,” Analytica Chimica Acta,Vol 48, 1969, p. 205.3For referenced ASTM standards, visit the

15、 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Bar

16、r Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States17. Apparatus7.1 Atomic-Absorption Spectrophotometer , for use at 313.3nm. A general guide for the use of flame atomic absorptionapplications is given in Practice D4691.NOTE 1The manufacturers instructions should be followed

17、 for allinstrumental parameters.7.1.1 Molybdenum Hollow-Cathode Lamp.7.2 Pressure-Reducing ValvesThe supplies of fuel andoxidant shall be maintained at a pressure somewhat higher thanthe controlled operating pressure of the instrument by suitablevalves.8. Reagents and Materials8.1 Purity of Reagents

18、Reagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it i

19、s first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, Type I, II, or III wat

20、er. Type I ispreferred and more commonly used. Type II water wasspecified at the time of round robin testing of these testmethods.NOTE 2The user must ensure the type of reagent water chosen issufficiently free of interferences. The water should be analyzed using thetest method.8.3 Ascorbic Acid Solu

21、tion (10 g/L)Dissolve1gofascorbic acid in water and dilute to 100 mL.8.4 Bromphenol Blue Indicator Solution (1 g/L)Dissolve0.1 g of bromphenol blue in 100 mL of 50 % ethanol orisopropanol.8.5 Hydrochloric Acid (1 + 49)Mix 20.0 mL of concen-trated hydrochloric acid (HCl, sp gr 1.19) with water and di

22、luteto1L.8.6 8-Hydroxyquinoline-Methyl Isobutyl Ketone Solution(10 g/L)Dissolve1gof8-hydroxyquinoline in 100 mL ofmethyl isobutyl ketone. Prepare fresh daily.8.7 Methyl Isobutyl Ketone (MIBK).8.8 Molybdenum Solution, Stock (1.0 mL = 100 g Mo)Dissolve 0.1500 g of molybdenum trioxide (MoO3)in10mLof wa

23、ter containing 1 mL of NaOH (100 g/L) (warm ifnecessary). Make just acid with HCl (1 + 49) and dilute to1000 mL with water. A purchased molybdenum stock solutionof appropriate known purity is also acceptable.8.9 Molybdenum Solution, Intermediate (1.0 mL = 1.0 gMo)Dilute 10.0 mL of molybdenum stock s

24、olution to 1000mL with water.8.10 Molybdenum Solution, Standard (1.0 mL = 0.1 gMo)Immediately before use, dilute 10.0 mL of intermediatemolybdenum solution of 100 mL with water. This standard isused to prepare working standards at the time of analysis.8.11 Nitric Acid (sp gr 1.42)Concentrated nitric

25、 acid(HNO3).8.12 Sodium Hydroxide Solution (100 g/L)Dissolve 100 gof sodium hydroxide (NaOH) in water and dilute to 1 L.8.13 MIBK-Saturated WaterThoroughly mix equal vol-umes of MIBK and water in a separatory funnel. Allow layersto separate. Collect and store water and MIBK, respectively, inproperly

26、 marked containers.8.14 Water-Saturated MIBKUse MIBK prepared from8.13.8.15 Nitrous OxideCommercially available nitrous oxideis suitable as oxidant.8.16 Acetylene FuelStandard, commercially availableacetylene is the usual fuel. Acetone, always present in acety-lene cylinders, will affect analytical

27、results. Generally, replac-ing the acetylene cylinder with 345 kPa (50 psi) remainingprevents acetone interference; however it has been reportedthat cylinders with pressure at 670 kPa (100 psi) or greater willcause interference.NOTE 3Warning: “Purified” grade acetylene contains a specialproprietary

28、solvent rather than acetone and should not be used. It canweaken the walls of poly(vinyl chloride) tubing that carries the acetyleneto the burner, causing a potentially hazardous situation.9. Sampling9.1 Collect the sample in accordance with Practices D3370.The holding time for the samples may be ca

29、lculated inaccordance with Practice D4841.9.2 To preserve the samples add concentrated HNO3(sp gr1.42) to a pH of 2 or less immediately at the time of collection;normally about 2 mL/L is required. If only dissolved molyb-denum is to be determined, filter the samples at time ofcollection through a 0.

30、45-m membrane filter before acidifica-tion.NOTE 4Alternatively, the pH may be adjusted in the laboratory if thesample is returned within 14 days. This could reduce hazards of workingwith acids in the field when appropriate.10. Standardization10.1 Prepare in 200-mL volumetric flasks a blank andsuffic

31、ient standards containing from 0.0 to 2.5 g of molybde-num by diluting 0.0 to 25.0-mL portions of the standardmolybdenum solution to 100 mL with water.10.2 Proceed as directed in 11.5 to 11.11.10.3 Construct an analytical curve by plotting the absor-bances of standards versus micrograms of molybdenu

32、m.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, 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 Pharmaco

33、peiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D3372 122NOTE 5The burner must be conditioned just prior to standardizationand running of sample extracts by aspirating water-saturated MIBK untilthe flame stabilizes. Some systems have required as long as 10 min fo

34、rconditioning.11. Procedure11.1 For total recoverable molybdenum, add 5 mL ofconcentrated nitric acid to 100 mL of the sample in a 250-mLErlenmeyer flask and mix well. Heat the sample, withoutboiling, on a steam bath or hot plate in a well-ventilated fumehood until the volume has been reduced to 15

35、to 20 mL.NOTE 6When treating samples of brine or a sample containing a largeamount of solids, the amount of reduction in volume is left to thediscretion of the analyst.NOTE 7Many laboratories have found block digestion systems auseful way to digest samples for trace metals analysis. Systems typicall

36、yconsist of either a metal or graphite block with wells to hold digestiontubes. The block temperature controller must be able to maintain unifor-mity of temperature across all positions of the block. For trace metalsanalysis, the digestion tubes should be constructed of polypropylene andhave a volum

37、e accuracy of at least 0.5%. All lots of tubes should comewith a certificate of analysis to demonstrate suitability for their intendedpurpose.11.2 If color in the digested solution indicates the presenceof partially oxidized materials, add additional acid and ap-proximately 90 mL of reagent water to

38、 the cooled solution andrepeat the digestion.11.3 Cool and filter the digested solution through a suitablefilter (such as a fine-textured, acid-washed, ashless paper) intoa 100-mL volumetric flask. Wash and filter paper two to threetimes with reagent water, collecting washings in flask; make upto vo

39、lume with reagent water.NOTE 8If only dissolved molybdenum is to be determined, filterportion of the sample through a 0.45-m membrane filter and proceed with11.4.11.4 Pipette a volume of sample containing less than 2.5 gof molybdenum (100 mL maximum) into a 200-mL volumetricflask and adjust the volu

40、me to 100 mL with water.11.5 Add 5 mL of ascorbic acid solution (8.3) and mix.11.6 Add 2 drops of bromphenol blue indicator solution(8.4) and mix.11.7 Adjust the pH by addition of NaOH (8.12) solution(100 g/L) until a blue color persists.Add HCl (1 + 49) by dropsuntil the blue color just disappears

41、in both the standards and thesample; then add 2.5 mL of HCl (1 + 49) in excess. The pH atthis point should be 2.3.NOTE 9The pH adjustment in 11.7 may be made with the use of a pHmeter instead of using an indicator.11.8 Add 5.0 mL of 8-hydroxyquinoline-MIBK solution(8.6) and shake vigorously for 15 m

42、in.11.9 Allow the layers to separate; then carefully add watersaturated with MIBK so as not to disturb the ketone layer untilit is completely in the neck of the flask.NOTE 10The ketone layer should be centrifuged to remove all tracesof water if the extract is to be stored for several hours before an

43、alysis.11.10 Zero the instrument while aspirating the water-saturated MIBK (8.13).11.11 Aspirate the ketone layer of standards and samplesinto the nitrous oxide-acetylene flame of the spectrophotometerand record the scale reading for each standard and sampleagainst the blank.NOTE 11Warning: Aspirati

44、ng methyl isobutyl ketone into a nitrousoxide-acetylene flame can be dangerous. To minimize the chances of anaccident, scrupulously follow recommended practices for using such asystem.12. Calculation12.1 Determine the weight of molybdenum in each sampleby referring to the analytical curve. Calculate

45、 the concentrationof molybdenum in micrograms per liter as follows:Molybdenum, g/L 5 1000/A! 3Bwhere:1000 = 1000 mL / LiterA = volume of sample, mL, andB = weight of molybdenum in sample, g.13. Precision and Bias513.1 The single-operator and overall precision of this testmethod within its designated

46、 range based on data from fourlaboratories, which includes a total of five operators analyzingeach sample on three different days, may be expressed asfollows:ST5 0.072X10.450SO5 0.039X10.610where:ST= overall precision, g/L,SO= pooled single-operator precision, g/L, andX = concentration of molybdenum

47、, g/L.13.2 Recoveries of known amounts of molybdenum (fromMoO3) added to a series of natural waters for the samelaboratories and operators were as follows:AmountAdded,g/LAmountFound,g/LBias % BiasStatisticallySignificant(95 %ConfidenceLevel)3.0 3.07 0.07 2.3 no9.5 9.38 0.12 1.3 no18.0 16.86 1.14 6.3

48、 yes13.3 This test method was evaluated with reagent andnatural water matrices. These data may not apply to waters ofother matrices.13.4 Practice D2777 requires a minimum of six independentlaboratories and analysts, respectively, for a collaborative studyof a test method. Since the numbers listed fo

49、r this study do notmeet these requirements, that deficiency is recorded here forthe benefit of the user of this test method.NOTE 12The nitric acid digestion steps were not performed in theround robin of this test method. It is an approved and recommendedpractice for determining total recoverable metals by atomic absorptionspectrometry; however, its use can be expected to increase the variability5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D19-1025.D3372 12