1、Designation: D 3718 85a (Reapproved 2005)Standard Test Method forLow Concentrations of Chromium in Paint by AtomicAbsorption Spectroscopy1This standard is issued under the fixed designation D 3718; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e of 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test
3、 method covers the determination of the contentof chromium (including chromium oxide) in the range between0.005 and 1.0 % present in the solids of liquid coatings or indried films obtained from previously coated substrates. Thereis no reason to believe that higher levels could not bedetermined by th
4、is test method, provided that appropriatedilutions and adjustments in specimen size and reagent quan-tities are made.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesa
5、fety 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. Specific hazardstatements are given in Section 7.2. Referenced Documents
6、2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 2832 Guide for Determining Volatile and NonvolatileContent of Paint and Related Coatings3. Summary of Test Method3.1 The sample of liquid coating or dried film is preparedfor analysis by dry ashing at 500C followed by digestion withpotassiu
7、m permanganate and sulfuric acid in a polytetrafluo-roethylene (PTFE)-lined acid decomposition vessel at anelevated temperature. The chromium in the filtered digestionmixture is determined by atomic absorption spectroscopy.4. Significance and Use4.1 The permissible level of heavy metals in certain c
8、oat-ings is specified by governmental regulatory agencies. This testmethod provides a fully documented procedure for determininglow concentrations of chromium present in both water- andsolvent-reducible coatings to determine compliance.5. Apparatus5.1 Atomic Absorption Spectrophotometer, consisting
9、of anatomizer and either a single- or three-slot burner; gas pressure-regulating and metering devices for nitrous oxide (N2O) andacetylene; a chromium hollow cathode lamp with a regulatedconstant current supply; a monochromator and associatedoptics; a photosensitive detector connected to an electron
10、icamplifier; and a readout device.5.2 Muffle Furnace, maintained at 500 6 10C.5.3 Force-Draft Oven, maintained at 105 6 2C.5.4 Acid Decomposition Vessel, with PTFE digestion cup.35.5 Hot Plate, with variable surface temperature controlover the range from 70 to 200C.5.6 Volumetric Flasks, 50, 100 and
11、 1000-mL.5.7 Pipets, 5, 10, 15, and 20-mL capacity.5.8 Filter Paper, ashless, medium filtering 15-cm.5.9 Paint Shaker.5.10 Crucibles, wide form, porcelain, approximately 30-mLcapacity.41This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Appl
12、ications and is the direct responsibility ofSubcommittee D01.21 on Chemical Analysis of Paints and Paint Materials.Current edition approved Jan. 1, 2005. Published February 2005. Originallyapproved in 1978. Last previous edition approved in 1999 as D 3718 85a (1999).2For referenced ASTM standards, v
13、isit 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.3The sole source of supply of an acid decomposition cup, (Catalog Number4745), known to the co
14、mmittee at this time is the Parr Instrument Co., 211Fifty-third St., Moline, IL 61265. If you are aware of alternative suppliers, pleaseprovide this information to ASTM International Headquarters. Your comments willreceive careful consideration at a meeting of the responsible technical committee,1wh
15、ich you may attend.4The sole source of supply of No. 25007 crucibles, known to the committee atthis time is Coors Co. If you are aware of alternative suppliers, please provide thisinformation to ASTM International Headquarters. Your comments will receivecareful consideration at a meeting of the resp
16、onsible technical committee,1whichyou may attend.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.11 Mortar and Pestle.5.12 Paint Draw-Down Bar.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unle
17、ss 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.5Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently
18、high purity to permit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Type II of Specification D 1193.6.3 Chromium Standard Stock Solution (1 mg/mL)Dissolve 3.735 g of
19、potassium chromate (K2CrO4) in 100 mLof water and dilute to 1 L.6.4 Chromium Standard Working Solution (0.1 mg/mL)Pipet 10 mL of the chromium standard stock solution into a100-mL volumetric flask and dilute to volume with water.6.5 Oxidizing SolutionDissolve 0.2 g of potassium per-manganate (KMnO4)
20、in 100 mL of H2SO4(1 + 1). Stir untilcompletely dissolved. The color of this solution is dark brown.6.6 Reducing SolutionDissolve1gofhydroxylaminehydrochloride (NH2OHHCl) in 100 mL of water.6.7 Reagent BlankPipet 5 mL of oxidizing solution into25 mL of water contained in a 50-mL volumetric flask. Ad
21、dreducing solution dropwise until the permanganate color hasbeen discharged; then dilute to 50 mL with water.6.8 Sulfuric Acid (1 + 1)Carefully add 1 volume of con-centrated H2SO4(sp gr 1.84) to 1 volume of water.6.9 Sulfuric Acid (5 % volume per volume)Carefully add50 mL of concentrated H2SO4(sp gr
22、 1.84) to 500 mL of waterand dilute to 1 L.7. Hazards7.1 Use care in handling concentrated H2SO4because it iscorrosive and may cause severe burns of the skin or eyes. Referto suppliers Material Safety Data Sheet.7.2 The National Institute for Occupational Safety andHealth has stated that hexavalent
23、chromium compounds arehazardous to health. Care should be exercised in preparation ofa sample for test. The wearing of a respirator and rubber orsynthetic gloves is recommended. In case of contact, washthoroughly with soap and water. Mixtures containing hexava-lent chromium compounds should not be f
24、lushed down a drainbut disposed of as hazardous waste.7.3 Use only a rubber bulb aspirator for pipetting liquids.8. Calibration and Standardization8.1 Prepare 50-mL quantities of at least four standardsolutions bracketing the expected chromium concentration inthe sample to be tested. To suitable ali
25、quots of the 100-ppmchromium standard working solution, add 10 mL of theoxidizing solution with a pipet, followed by the dropwiseaddition of reducing solution until the permanganate color hasbeen discharged, then dilute to 50 mL with water.8.2 Operational instructions for atomic absorption spectro-p
26、hotometers vary with different models. Consult the manufac-turers literature for establishing optimum conditions for thespecific instrument used.8.3 Turn the instrument on and set the wavelength to the357.9-nm chromium line. Apply the recommended current tothe chromium hollow-cathode lamp. Allow the
27、 instrument towarm up for about 15 min and set the slit width. Adjust thenitrous oxide and acetylene pressures and ignite the burneraccording to instructions.8.4 Aspirate water to rinse the atomizer chamber. Aspirate astandard solution and make any necessary readjustment ininstrument parameters to o
28、btain maximum absorption. Zero theinstrument while aspirating reagent blank solution (6.7). Aspi-rate each of the appropriate standard solutions and record thecorresponding instrument readings. Aspirate water betweeneach standard.8.5 Transfer a 25-mL aliquot from each of the standardsolutions prepar
29、ed in 8.1 to 50-mL volumetric flasks and diluteto volume with water. Repeat the steps outlined in 8.4 for thediluted aliquot solutions.8.6 Construct a calibration curve on linear graph paper byplotting the absorbance versus concentration (micrograms permillilitre) for each set of standard solutions.
30、NOTE 1To obtain maximum accuracy one should complete calibra-tion and standardization just prior to sample analysis.9. Procedure9.1 If the sample is a liquid coating, mix it until homoge-neous, preferably on a mechanical paint shaker. Determine thenonvolatile content in accordance with Guide D 2832.
31、9.2 Determine the ash content of the material under test induplicate.9.2.1 Weigh to the nearest 0.1 mg approximately5gofliquid coating or3gofdried film into each of two taredporcelain crucibles.NOTE 2Recover dried paint films from previously coated substrates(being careful not to remove any underlyi
32、ng material from the substrate)or prepare in the laboratory from liquid samples. For the laboratorypreparation, flow some of the well-mixed sample onto a clean glass plate.The use of a paint draw-down bar is recommended to obtain a uniformfilm thickness not exceeding 2 mils (50 m). Allow the film to
33、 dry in anoven at 105C for a minimum of 1 h. Scrape the dried film off the glassplate, preferably with a single-edge razor blade.9.2.2 Place the crucibles containing the liquid coating on thehot plate and slowly increase the temperature until the materialis dried. With some types of coatings, an ini
34、tial oven-drying at105C may be necessary to remove solvents without incurringlosses due to spattering.9.2.3 When the specimen appears to be dry, or when startingwith a dried film, gradually increase the temperature of the hotplate until the material chars.9.2.4 After charring is complete, place the
35、crucibles in themuffle furnace and ash at 500C.5Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole
36、, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D 3718 85a (2005)29.2.5 When the ashing appears to be complete (approxi-mately 1 to 2 h), remove the crucibles from the muffle furnaceand allow to cool to room temperatu
37、re in a desiccator. Weighand calculate the mean value for the percent ash.9.3 Transfer each ash to a clean, dry mortar and grind to afine, uniform powder. Weigh to the nearest 0.1 mg, 0.02 to 0.2g of each ash directly into separate decomposition vesselinserts.NOTE 3For a material containing 50 ppm (
38、mg/kg) of chromium basedon the solids and having 50 % ash and 70 % nonvolatile material, 0.2 g ofash extracted and diluted to 50 mL will contain 0.28 g of chromium permillilitre, and for one containing 10 000 ppm, 0.02 g of ash extracted anddiluted to 100 mLwill contain 2.8 g of chromium per millili
39、tre. To ensurecomplete recovery of chromium, do not use more than 0.05 g of ash formaterials that are known or suspected to contain over 1000 ppm ofchromium based on the solids.9.4 Pipet exactly 10 mL of oxidizing solution into the cup.Swirl gently to facilitate mixing. Place the vessel in a circu-l
40、ating oven at 105C for 112 h.9.5 Remove the vessel from the oven and allow to coolslowly to ambient temperature. Do not cool by placing thevessel in a refrigerator or freezer, or by submerging it in acooling liquid. When cooled, carefully unseal the vessel in afume hood.NOTE 4When the vessel is disa
41、ssembled, if the solution does notshow the presence of excess permanganate, repeat the digestion using asmaller weight of ash.9.6 Quantitatively filter the contents through filter paperdirectly into a 50 or 100-mL volumetric flask. Rinse thedigestion cup several times with water, transferring any in
42、-soluble material to the filter paper. Wash the filter paper severaltimes with small volumes of water. Add hydroxylamine hydro-chloride solution dropwise to the filtrate until the permanganatecolor has been discharged, then dilute to volume with water.9.7 Aspirate each test solution and determine th
43、e absor-bance in the same manner in which the instrument wascalibrated. Determine the concentration of chromium in micro-grams per millilitre from the appropriate calibration curve. Ifthe absorbance is above the range covered by the calibrationcurve, dilute an aliquot of the test solutions to a suit
44、ablevolume with H2SO4(5 % volume per volume) and repeat thedeterminations.NOTE 5The method of standard additions may be used to improve theaccuracy of the analysis. This test method is particularly recommended foruse with unknown samples where matrix effects may be potentiallysignificant. For a deta
45、iled description of the procedure and calculationsused in the method of standard additions, consult a standard text on atomicabsorption spectroscopy or the instruction manual provided by theinstrument manufacturer.10. Calculation10.1 Calculate the mean concentration of chromium in thenonvolatile por
46、tion of the sample as follows:Chromium, ppm mg/kg! in nonvolatile 5 C 3 F 3 A 3 V!/S 3 NV!(1)where:C = concentration of chromium in the aspirated testsolution, g/mL,F = dilution factor from 9.7 (volume diluted to volume ofaliquot),A = mean percent ash as determined in 9.2.5,V = volume diluted to in
47、9.6 (50 or 100 mL),S = weight of ash, andNV = percent nonvolatile of paint sample (use 100 ifsample was a dried film).11. Report11.1 Report the chromium content of the nonvolatile portionof the sample tested and whether the analysis was conducted ona liquid coating or a dried film.12. Precision and
48、Bias612.1 The precision estimates are based on an interlaboratorystudy in which six different laboratories analyzed in duplicate,on two different days, four samples of water-reducible paintsand four samples of solvent-reducible paints containing from50 to 10 000 ppm (mg/kg) chromium. The within-labo
49、ratorycoefficient of variation was found to be 4.9 % relative at 39degrees of freedom and the between-laboratory coefficient ofvariation was 8.5 % relative at 31 degrees of freedom. Basedon these coefficients, the following criteria should be used forjudging the acceptability of results at the 95 % confidencelevel:12.1.1 RepeatabilityTwo results, each the mean of dupli-cate determinations, obtained by the same operator on differentdays should be considered suspect if they differ by more than14 % relative.12.1.2 ReproducibilityTwo results, each the m
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