1、Designation: D 5281 98 (Reapproved 2005)Standard Test Method forCollection and Analysis of Hexavalent Chromium in AmbientAtmospheres1This standard is issued under the fixed designation D 5281; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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.1. Scope1.1 This test method covers the collection and measurementof hexavalent chromium Cr(VI) in the ambi
3、ent atmosphere.1.2 This test method collects and stabilizes atmospherichexavalent chromium using an alkaline impinger buffer solu-tion in a wet impingement sampling technique. Lead chromatePbCrO4, generally considered poorly soluble in water, issoluble in the impinger solution up to 940 g/L as hexav
4、alentchromium.1.3 This test method measures hexavalent chromium usingan ion chromatographic separation combined with a postseparation reaction with a colorimetric reagent and photometricdetection.1.4 This test method is applicable in the range from 0.2 to100 ng/m3of hexavalent chromium in the atmosp
5、here assum-ing 20 m3of air sample. The range can be extended upwards byappropriate dilution.1.5 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in parentheses are forinformation only.1.6 This standard does not purport to address all of thesafety concerns,
6、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 Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 1356
7、Terminology Relating to Sampling and Analysis ofAtmospheresD 1357 Practice for Planning the Sampling of the AmbientAtmosphereD 2914 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D 3195 Practice for Rotameter CalibrationD 3586 Test Method for Chromium in Workplace Atmo-s
8、pheres (Colorimetric Method)33. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D 1356.3.2 Definitions of Terms Specific to This Standard:3.2.1 eluentthe ionic mobile phase used to transport thesample through the ion exchange column.3.2.2 resol
9、utionthe ability of a column to separate con-stituents under specified test conditions.4. Summary of Test Method4.1 Sample Collection:4.1.1 Air is drawn at a rate of 15 L/min over a continuous24-h period through three 500-mL glass impingers (in-line)filled with 0.02 N sodium bicarbonate NaHCO3 “buff
10、er”solution. A target air volume of 20 m3is sampled.4.1.2 Impinger buffer solution has a pH of 8.2 and wasselected to prevent hexavalent chromium from being reducedto trivalent chromium Cr(III) in an acidic medium duringsampling (4).4.1.3 The impinger buffer solution from each impinger isanalyzed fo
11、r hexavalent chromium.4.2 Sample Analysis (1, 2, 3, 4)4:4.2.1 A volume of filtered sample, typically 1 mL, isinjected into the eluent flow path and separated by anionexchange using an ammonium sulfate (NH4)2SO4 basedeluent.4.2.2 After separation, the sample is reacted with an acidicsolution of diphe
12、nylcarbohydrazide. Hexavalent chromium1This test method is under the jurisdiction of ASTM Committee D22 on AirQuality and is the direct responsibility of Subcommittee D22.03 on AmbientAtmospheres and Source Emissions.Current edition approved March 1, 2005. Published May 2005. Originallyapproved in 1
13、992. Last previous edition approved in 1998 as D 5281 - 98.2For 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 onthe ASTM website.3W
14、ithdrawn.4The boldface numbers in parentheses refer to a list of references at the end ofthe text.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.reacts selectively with this reagent to form the characteristicviolet colored complex.4
15、.2.3 The eluent stream passes through a photometric de-tector for detection of the chromium diphenylcarbohydrazidecomplex by visible absorbance at 520 nm. Absorbance isproportional to the hexavalent chromium concentration.5. Significance and Use5.1 Hexavalent chromium has been shown to be a humanres
16、piratory carcinogen in epidemiological studies when hu-mans are exposed to relatively high airborne concentrations.Such high exposures may also induce dermal sensitization tohexavalent chromium in humans (5).5.2 Ambient atmospheric concentrations of hexavalentchromium are well below detection limits
17、 of sampling methodsincluding Test Method D 3586 and NIOSH-7600 (1).5.3 Objective assessment of ambient atmospheric concen-trations of hexavalent chromium provides a means of evaluat-ing exposures to atmospheric hexavalent chromium in amanner that can be related to health-based risk levels. Collect-
18、ing such actual monitoring data reduces or eliminates the needfor theoretical resuspension modeling and provides improvedbasis for health assessments of potential exposures (5).5.4 The buffered impinger sampling technique provides pHcontrol of the sampling medium, which stabilizes the oxidationstate
19、 of hexavalent chromium during sampling (6).5.5 Ion chromatography provides a means of separating thehexavalent chromium from other species present in the sample,many of which interfere with other detection methods. Thecombination of this separation with a sensitive colorimetricdetection method prov
20、ides a selective and sensitive analyticalmethod for hexavalent chromium with minimal sample prepa-ration (4).6. Interferences6.1 Reducing agents may reduce hexavalent chromium totrivalent chromium in acidic matrices. Preservation of a pH 7.8or greater will minimize the effect of these species. Theox
21、idation of trivalent chromium to hexavalent chromiumduring this test method is unlikely to occur (6).6.2 By virtue of the chromatographic separation, essentiallyall interfering species are removed from the hexavalent chro-mium before detection. The response of 1 mg/L of hexavalentchromium is not aff
22、ected by 1000 mg/L of chromic ion.6.3 Interferences may result from overloading of the ana-lytical separator column capacity with high concentrations ofanionic species in the sample. Concentrations of chloride ion orsulfate ion up to the equivalent of 2 % NaCl and 5 % Na2SO4do not affect the separat
23、ion or detection when using a 100-Lsample loop (2).6.4 Hypochlorite OCl1 (100 mg/L) in the buffer solutionhas been found to cause a positive interference with hexavalentchromium analyses to the extent of 0.3 to 1 g/L. Hypochlorite(1 mg/L) has also been found, in the presence of 50 g/Ltrivalent chrom
24、ium, to cause a 1.2-g/L positive interferencewith hexavalent chromium.6.5 Permanganate MnO41 (0.5 g/L) causes a positive0.07-g/L interference with hexavalent chromium.6.6 No other interferences were observed from 10 g/LBrO3, MoO42, ClO4,S2O82,VO43,Be+,Cu+2,Ni+2,Ag+,Tl+3,V+3,As+3,Ba+2,Cd+2,Co+2,Cr+3,
25、Mo+5,Sb+3,Zn+2,Pb+2,F,Cl,Br,NO3,NO2,P2O64,SO42, 100 mg/L Se,or 1 mg/L Hg (6).7. Apparatus7.1 Sampling Apparatus:7.1.1 Impinger Sampling TrainFor a schematic drawingof the major sampling train components see Fig. 1. Thesampling train for collecting particulate matter and hexavalentchromium consists o
26、f the following elements:7.1.1.1 ImpingersThree 500-mL impingers (in-line) areused in the sampling train. The first two impingers in the series(A and B) use nozzled impinger inlets with impaction plates.These impingers impinge air at high velocity against theimpaction plate creating smaller air bubb
27、les which providemore surface area for air contact with buffer solution. The thirdimpinger (C) has a straight inlet nozzle and no impaction plate.7.1.1.2 Impinger Buffer Solution0.02 N sodium bicarbon-ate buffer solution (see 8.3.1) is added to the impingers suchthat: Impinger A = 250 mL, B = 200 mL
28、, and C = 150 mL.These particular impinger sodium bicarbonate solution vol-umes are recommended to minimize post sample volumedisparities between impingers.7.1.2 The sampling train apparatus is interconnected by thefollowing elements:7.1.2.1 Sample Line/ProbeSample is drawn from ambientair through a
29、 sample line/probe that consists of a 100 toFIG. 1 Diagram of a Sampling Train and Sampling ApparatusD 5281 98 (2005)2150-mm polytetrafluoroethylene (PTFE) tube (12-mm (12-in.)outside diameter and 9-mm (38-in.) inside diameter). Thesample line/probe is inserted into the air inlet of the firstImpinge
30、r (A).7.1.2.2 Impingers A, B, and C are interconnected using twoglass impinger U-joints. The last impinger in the series (C) isconnected to the sample pump by means of vinyl tubing usinga glass 0.5p radian (90) angle impinger joint that adapts theimpinger to wax film tubing (see 7.1.3). Impinger cli
31、ps, wax,and wax film wraps are used to secure all impinger connectionsand prevent sampling train leaks.7.1.3 Sampling BoxA pre-assembled impinger samplingbox holds the impinger sampling train and is designed so thatthe sample line/probe protrudes outside the box and bendsdownward. The sample box is
32、fitted with vinyl tubing (14-mm(916-in.) outside diameter and 9-mm (38-in.) inside diameter)that connects the impinger sampling train to a sample pump(see 7.1.2.2).The vinyl tubing is fitted with an in-line rotameterto facilitate sampling train operational checks.7.1.3.1 An in-line rotameter fitted
33、on the sample box facili-tates operational checks of the sampling system. The rotameteris a glass variable area flow meter capable of measuringflowrates between 10 and 15 L/min, calibrated in accordancewith Practice D 3195.7.1.3.2 Leakless Sample PumpA vane-axial electricallyoperated sampling pump c
34、apable of drawing 10 to 18 L/min ofair through the sampling train over 24 h is suitable.7.1.3.3 Flow Control DeviceAir flowrate control can beenhanced using a critical orifice or dry gas meter in accordancewith Test Methods D 2914. Protect the orifice or gas meterfrom particulate matter (see 11.2.6)
35、.7.1.4 Bubble MeterThe bubble meter is used as a primarymethod of sampling train air flowrate calibration (see 10.1) andshall be capable of reading sampling air flowrates of 2 to 30L/min. Connect the bubble meter to the sample line/probe witha flexible rubber tube.7.1.5 An elapsed time meter is plac
36、ed in line with thesample pump to assist in detection of electrical interruptionsthat could have occurred over the 24 h interval.7.1.6 Stop Watch or Timer.7.1.7 pH Meter, to measure the pH of the impinger buffersolution.7.1.8 Refrigerator or Ice Cooler, for storage of samplesprior to shipment to the
37、 laboratory (see 11.4).7.1.9 Ice Cooler, for transport of samples to the laboratory(see 11.4).7.1.10 Meteorological Weather Station or Weather DataService, to determine ambient temperature, pressure, relativehumidity, wind speed and direction, and precipitation (see11.2.7). This information may be u
38、seful to interpret data, but isnot required to correct data for standard conditions.7.2 Analytical Apparatus (4):7.2.1 Ion ChromatographThe ion chromatograph shallhave the following components as shown in Fig. 2.7.2.1.1 Pump, capable of delivering a constant flow in therange of 1 to 5 mL/min at a pr
39、essure of 15 to 150 MPa (200 to2000 lb/in.2).7.2.1.2 Injection ValveA low dead-volume valve that willallow the loading of a sample contents into the eluent stream.Sample loops of up to 1 mL will provide enhanced detectionlimits. Smaller sample loops will result in proportionallyhigher detection limi
40、ts.7.2.1.3 Guard ColumnA column placed before the sepa-rator column to protect the separator column from fouling byparticles or strongly absorbed organic constituents.7.2.1.4 Separator ColumnA column packed with highcapacity pellicular anion exchange resin that is suitable forresolving hexavalent ch
41、romium from a sample containing hightotal dissolved solids (for example, 3 % Na2SO4).7.2.1.5 Reagent Delivery ModuleA device capable ofdelivering 0 to 2 mL/min of reagent against a backpressure ofup to 40 kPa (6.0 lb/in.2).7.2.1.6 Mixing Tee and Reaction CoilA device capable ofmixing two flowing str
42、eams with minimal band spreading.7.2.1.7 DetectorA low-volume, flow-through visible ab-sorbance detector with a nonmetallic 1-cm flow path. Thedetection wavelength for hexavalent chromium is 520 nm.7.2.1.8 Recorder, Integrator, or ComputerA device com-patible with detector output, capable of recordi
43、ng detectorresponse as a function of time for the purpose of measuringpeak height or area.7.2.2 Eluent ReservoirA container suitable for storingeluent.7.2.3 0.45 m syringe filter, for sample filtration prior toanalysis (see 11.5.7).FIG. 2 Diagram of an Ion Chromatograph Using Post-ColumnReagent Addi
44、tion and Photometric DetectionD 5281 98 (2005)37.2.4 SyringeAsyringe equipped with a male fitting and acapacity of at least 1 mL or auto sampler module (see 11.5.8).8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused in all tests.All reagents shall conform to the spec
45、ificationsof the Committee on Analytical Reagents of the AmericanChemical Society where such specifications are available.58.2 Purity of WaterWater shall be Type II reagent waterconforming to Specification D 1193.8.3 Sampling Reagents and Materials:8.3.1 Impinger Buffer Solution0.02 N sodium bicarbo
46、natebuffer solution: dissolve 1.67 g of sodium bicarbonate(NaHCO3) in 1 L of reagent water.8.3.2 Impinger Buffer Solution SpikePrepared in 0.5, 1,and 10-g/L concentrations by diluting appropriate volumes ofthe 1000 g/L hexavalent chromium standard (see 8.5.2)inthebuffer solution (see 8.3.1).8.3.3 1
47、% Nitric Acid Wash SolutionDilute 10 mL ofconcentrated reagent grade nitric (HNO3) acid, sp gr 1.42, to 1L with water.8.4 Ion Chromatography Eluents:8.4.1 Eluent Concentrate (2.0 M (NH4)2SO4, 1.0 MNH4OH)Dissolve 264 g of ammonium sulfate (NH4)2SO4inabout 500 mLof water.Add 65 mLof concentrated ammon
48、iumhydroxide (NH4OHsp gr 0.90). Mix well and dilute to 1 L ina volumetric flask.8.4.2 Eluent (0.20 M (NH4)2SO4, 0.1 M NH4OH)Add100 mL of eluent concentrate (see 8.4.1) to a 1-L flask anddilute to volume with water.8.4.3 Diphenylcarbohydrazide ReagentDissolve 0.5 g of1,5-diphenylcarbohydrazide in 100
49、 mLof reagent grade metha-nol. Add to about 500 mL of water containing 28 mL of 96 %sulfuric acid (sp gr 1.84). Dilute with water to 1 L in avolumetric flask.8.5 Calibration Standards:8.5.1 Hexavalent Chromium Solution, Stock (1000 mg Cr/L)Dissolve 0.2828 g of potassium dichromate (K2Cr2O7)that has been dried at 105C for 1 h, in water. Dilute to 100 mLin a volumetric flask.8.5.2 Hexavalent Chromium Solution, Standard (1000 gCr/L)Pipet 1.00 mL of the chromium stock solution (see8.5.1) into a 1-L volumetric fl
