1、Designation: D 4785 08Standard Test Method forLow-Level Analysis of Iodine Radioisotopes in Water1This standard is issued under the fixed designation D 4785; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 quantification of low levelsof radioactive iodine in water by means of chemical separationand counting
3、 with a high-resolution gamma ray detector.Iodine is chemically separated from a 4-L water sample usingion exchange and solvent extraction and is then precipitated ascuprous iodide for counting.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are provi
4、ded forinformation purposes only.1.3 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 of regulatory limitat
5、ions prior to use. For specific hazardstatements, see Note 2, Note 3, Note 9, and Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Commit
6、tee D19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 3648 Practices for the Measurement of RadioactivityD 3649 Practice for High-Resolution Gamma-Ray Spec-trometry of WaterD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD 385
7、6 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of Water3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D 1129.4. Summary of Test Method4.1 Sodium iodide is added as a carrier prior to performingany chemical
8、separations. The samples undergo an oxidation-reduction process to ensure exchange between the carrier andthe radioactive iodide. Hydroxylamine hydrochloride and so-dium bisulfite are added to convert all the iodine to iodidewhich is then removed by anion exchange. Subsequent elutionof the iodide is
9、 followed by oxidation-reduction to elementaliodine. The elemental iodine is purified by solvent extraction,reduced to iodide, and precipitated as cuprous iodide. Thechemical recovery is determined from the recovery of theiodide carrier.5. Significance and Use5.1 This test method was developed for m
10、easuring lowlevels of radioactive iodine in water. The results of the test maybe used to determine if the concentration of several radioiso-topes of iodine in the sample exceeds the regulatory statutes fordrinking water. With a suitable counting technique, samplesize, and counting time, a detection
11、limit of less than 0.037Bq/L (1 pCi/L) is attainable by gamma-ray spectroscopy. Thismethod was tested for131I . Other iodine radioisotopes shouldbehave in an identical manner in this procedure. However,other iodine radioisotopes have not been tested according toPractice D 2777. The user of this meth
12、od is responsible fordetermining applicability, bias, and precision for the measure-ment of other iodine radioisotopes using this method.5.2 This procedure addresses the analysis of iodine radio-isotopes with half-lives greater than 2 hours, which include121I,123I,124I,125I,126I,129I,130I,131I,132I,
13、133I, and135I.6. Interferences6.1 Stable iodine in the sample will interfere with thechemical recovery determination. One milligram of ambientiodine would produce a bias of about 4 %.6.2 There are numerous characteristic iodine X-rays at andbelow 33.6 keV which are indicative of iodine, but not aspe
14、cific radioisotope of iodine. It is recommended that onlydiscreet gamma energy lines at and above 35.5 keV be used foridentification and quantification of iodine radioisotopes.7. Apparatus7.1 Analytical Balance, readable to 0.1 mg.1This test method is under the jurisdiction of ASTM Committee D19 on
15、Waterand is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemi-cal Analysis.Current edition approved April 1, 2008. Published April 2008. Originallyapproved in 1988. Last previous edition approved in 2000 as D 4785 00a.2For referenced ASTM standards, visit the ASTM website, ww
16、w.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 Box C700, West Conshohocken, PA 19428-2959, United States.7.2
17、Flexible Polyvinyl Chloride (PVC) Tubing, 6.35 mm (14in.) outside diameter, 1-m length.7.3 Gamma-Ray Spectrometry Systemhigh resolutiongamma spectrometer (high purity germanium or equivalent)with a useful energy range of approximately 30 keV to 1800keV (see Practice D 3649).7.4 Glass Fiber Filter Pa
18、per, 11.5-cm diameter.7.5 Ion Exchange Column, glass tube, 35 6 2-mm insidediameter, 150-mm length, fitted with No. 8 one-hole rubberstoppers and perforated disk.7.6 Membrane Filters, 0.4 or 0.45-m pore size, 25-mmdiameter, with suitable filter holder and vacuum filter flask.7.7 Peristaltic Tubing P
19、ump, variable speed, fitted withvinyl or silicone tubing.7.8 pH Meter.7.9 Sintered Glass Filter, Bchner funnel, 150-mL size,medium or coarse porosity with suitable one-hole stopper andvacuum filter flask.7.10 Vacuum Desiccator.7.11 Vortex Mixer.8. Reagents and Materials8.1 Purity of ReagentsReagent
20、grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee onAnalytical Reagents of theAmerican Chemical Society.3Other grades may be used provided they are of sufficiently highpurity to permit their us
21、e without reducing the accuracy of thedetermination.8.2 Purity of Water Unless otherwise indicated, referenceto water shall be understood to mean reagent water conformingto Specification D 1193, Type III.8.3 Radioactive PurityRadioactive purity shall be suchthat the measured radioactivity of blank s
22、amples does notexceed the calculated probable error of the measurement.8.4 Ammonium Hydroxide (sp gr 0.90)Concentrated am-monium hydroxide (NH4OH).8.5 Ammonium Hydroxide (1.4 M)Mix one volume ofconcentrated NH4OH (sp gr 0.90) with nine volumes of water.8.6 Anion Exchange ResinStrongly basic, styrene
23、, quar-ternary ammonium salt, 2050 mesh, chloride form, Dowex1-X8, or equivalent.8.7 Cuprous Chloride Solution (approximately 10 mg CuCl/mL)Dissolve 10 g of CuCl (99.99 %) in 26 mL of concen-trated HCl (sp gr 1.19). Add this solution to 1000 mL of NaClsolution (1 M) slowly with continuous stirring.
24、Add a smallquantity of metallic copper (for example, 5 to 10 copper metalshot) to the solution for stabilization.4Store the CuCl in adesiccator.8.8 Hydrochloric Acid (sp gr 1.19)Concentrated hydro-chloric acid (HCl).8.9 Hydrochloric Acid Solution (0.3 M)Dilute 25 mL ofconcentrated HCl to 1000 mL wit
25、h water.8.10 Hydroxylamine Hydrochloride (NH2OH:HCl)Crystals.8.11 Iodide Carrier Solution (25 mg I/mL)Dissolve 14.76g of NaI in approximately 80 mL of water in a 500-mLvolumetric flask and dilute to volume. Standardize using theprocedure in Section 10.8.12 Iodine-131 Standardizing SolutionNational s
26、tan-dardizing body such as National Institute of Standards andTechnology (NIST), traceable solution with a typical concen-tration range from 1 to 10 kBq/mL.8.13 Nitric Acid (sp gr 1.42)Concentrated HNO3.8.14 Nitric Acid (1.4 M)Mix 1 volume of concentratedHNO3(sp gr 1.42) with 10 volumes of water.8.1
27、5 Sodium Bisulfite Solution (2 M)Dissolve 104.06 gof NaHSO3in approximately 300 mL of water in a 500-mLvolumetric flask and dilute to volume.8.16 Sodium Chloride Solution (1 M)Dissolve 58.45 g ofNaCl in approximately 500 mL of water in a 1000 mLvolumetric flask and dilute to volume.8.17 Sodium Hydro
28、xide Solution (12.5 M)Dissolve 500 gof NaOH in 800 mL of water and dilute to 1 L.NOTE 1Caution: The dissolution of sodium hydroxide may produceexcessive heat.8.18 Sodium Hypochlorite (NaOCl)Approximately 5 to6 %. Commercially available bleach is acceptable.NOTE 2Warning: Acidification of NaOCl produ
29、ces toxic chlorinegas and must be handled in a fume hood.8.19 Toluene.NOTE 3Warning: Toluene is a carcinogen and must be handled anddisposed of in an approved manner.8.20 Calibration standard(s)Known amounts of125I,129I,and131I are used for calibration when determining theseradionuclides. A mixed-ga
30、mma standard, forexample,241Am,109Cd,57Co,141Ce,113Sn,137Cs,88Y,and60Co, is used for calibration over an extended energy rangeas required for the determination of additional radioisotopes ofiodine. These standards should be mounted on the filter asdescribed in 7.6. The known amounts of the radionucl
31、ides mustbe traceable to a national standardizing body such as NIST inthe USA. The standard may be prepared by the laboratory3Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Ch
32、emical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.4CuCl solution is not stable. It can be oxidized to the Cu+2state by air after aperiod of ti
33、me, when the solution will turn dark green. If this happens, prepare afresh solution. The shelf life of the solution can be extended by displacing the airover the remaining solution with nitrogen or argon gas after each use and thenclosing the container promptly.D4785082performing this method or by
34、a commercial supplier of suchstandards. Alternate radionuclides may be used for calibrationprovided that they have gamma ray energies covering the rangeof interest for the iodine radionuclides to be analyzed.9. Hazards9.1 Due to the potential health effects from handling thesecompounds, the steps ut
35、ilizing NaOCl and toluene must becarried out in a fume hood. Toluene is a carcinogen andacidification of NaOCl liberates toxic Cl2gas.10. Standardization of Iodide Carrier10.1 Pipet 1.0 mL of iodide carrier reagent into each of five100-mL centrifuge tubes containing 50 mL of deionized water.10.2 Add
36、 0.1 mL of 2 M NaHSO3to each solution and stirvigorously using a vortex mixer. Add 5.0 mL of freshlyprepared CuCl solution.10.3 Using a pH meter, check the pH of each solution andadjust the pH to between 2.40 to 2.50 with 0.3 M HCl or 1.4 MNH4OH.10.4 Place each solution in a warm (approximately 50 t
37、o60C) water bath for 5 to 10 min, stirring occasionally.10.5 Rinse each CuI precipitate onto a separate preweighed0.45-m membrane filter mounted in a vacuum filtrationassembly. Rinse the walls of the filter holder with approxi-mately 50 mL of water.10.6 Dry all samples in a vacuum desiccator for a m
38、inimumof 60 min or to constant weight. Remove and weigh the filterand precipitate. Record all data.10.7 Determine the net weight of each CuI precipitate.10.8 Use the mean of the five weights for the standardweight. The relative standard deviation of the mean should notexceed 0.025.11. Calibration of
39、 High-resolution Gamma-raySpectroscopy System11.1 Accumulate an energy spectrum using the calibrationstandard (8.20) traceable to a national standards body, in thegeometrical position representing that of the samples to beanalyzed. Accumulate sufficient net counts (total counts minusthe Compton base
40、line) in each full-energy gamma-ray peak ofinterest to obtain a relative standard counting uncertainty of#1%.11.2 Using the gamma-ray emission data from the calibra-tion standard and the peak location data from the calibrationspectrum, establish the energy per channel relationship (energycalibration
41、) as:En 5 Offset 1 Ch 3 Slope! (1)where:En = peak energy (keV),Offset = energy offset for the energy calibration equation(keV),Ch = peak location channel number, andSlope = energy calibration equation slope (keV per chan-nel).NOTE 4Most modern spectroscopy software packages perform thiscalculation,
42、and may include higher-order polynomial terms to account forminor non-linearity in the energy calibration.11.3 Using the gamma emission data from the calibrationstandard and the peak resolution data from the calibrationspectrum, establish the resolution versus energy relationship(energy calibration)
43、 as:FWHM 5 Offset 1 Ch 3 Slope! (2)where:FWHM = full width of the peak at one-half the maximumcounts in the centroid channel (keV),Offset = width offset for the resolution calibration equa-tion (keV),En = peak energy (keV), andSlope = resolution calibration equation slope (keV/keV).NOTE 5Most modern
44、 spectroscopy software packages perform thiscalculation, and may include higher-order polynomial terms to account fornon-linearity in the resolution calibration.11.4 For each gamma-ray photopeak, calculate the full-energy peak efficiency, ef, as follows:ef5RnRg3 DF(3)where:ef= full-energy peak effic
45、iency (counts per gamma rayemitted),Rn= net gamma-ray count rate in the full-energy peak ofinterest, counts per second (s1),Rg= gamma-ray emission rate, in gamma-rays per second(s1), as of the reference date and time of thecalibration standard,DF = decay factor for the calibrating radionuclide, el(t
46、1t0),l = (ln 2) / t1/2,t1/2= half-life of calibrating radionuclide (half-life unitmust match that used for the time difference, t1t0),t0= reference date and time of the calibration standard,andt1= midpoint of sample count (date and time).11.5 Many modern spectrometry systems are computerizedand the
47、determination of the gamma-ray detection efficienciesis performed automatically at the end of an appropriatecounting interval. Refer to the manufacturer instructions forspecific requirements and capabilities.11.6 Plot the values for the full-energy peak efficiency (asdetermined in Section 11.5) vers
48、us gamma-ray energy. Com-pare the efficiency curve to the typical efficiency curve for thedetector type. The curve should be smooth, continuous andhave a shape similar to the detector being used. The plot willallow the determination of efficiencies at energies throughoutthe range of the calibration
49、energies and will show that thealgorithms used in computerized systems are providing validefficiency calibrations. Select the fit that has the best 95 %confidence limit around the fitted curve, has all data pointswithin 68 % of the value of the fitted curve, or both. This isaccomplished by calculating the bias between the actualefficiency and the efficiency calculated with the fitted curve.11.7 Save or store the values of energy versus efficiency forfuture reference, to be used in the calculation of activity foreach iodine nuclide in Section 14.
