ASTM D4785-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D4785 − 08 (Reapproved 2013) D4785 − 20
Standard Test Method for
Low-Level Analysis of Iodine Radioisotopes in Water
This standard is issued under the fixed designation D4785; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Warning notes were editorially updated throughout in June 2013.
1. Scope
1.1 This test method covers the quantification of low levels of radioactive iodine in water by means of chemical separation and
counting with a high-resolution gamma ray detector. Iodine is chemically separated from a 4-L 4 L water sample using ion
exchange and solvent extraction and is then precipitated as cuprous iodide for counting.
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for
information purposes only.only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. For specific hazard statements, see 8.178.16, 8.188.17, 8.198.18, Section 9, and 13.2.11.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Flowing Process Streams
D3648 Practices for the Measurement of Radioactivity
D3649 Practice for High-Resolution Gamma-Ray Spectrometry of Water
D4448 Guide for Sampling Ground-Water Monitoring Wells
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
D3856D6001 Guide for Management Systems in Laboratories Engaged in Analysis of WaterDirect-Push Groundwater Sampling
for Environmental Site Characterization
D7282 Practice for Set-up, Calibration, and Quality Control of Instruments Used for Radioactivity Measurements
D7902 Terminology for Radiochemical Analyses
2.2 Other Documents:
ANSI N42.22 Traceability of Radioactive Sources to the National Institute of Standards and Technology (NIST) and Associated
Instrument Quality Control
BIPM-5 Decay Data Evaluation Project (DDEP)
NUDAT2
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.04 on Methods of Radiochemical
Analysis.
Current edition approved June 15, 2013May 1, 2020. Published July 2013June 2020. Originally approved in 1988. Last previous edition approved in 20082013 as
ɛ1
D4785 – 08.D4785 – 13 . DOI: 10.1520/D4785-08R13E01.10.1520/D4785-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Available from Institute of Electrical and Electronics Engineers, Inc. (IEEE), 445 Hoes Ln., Piscataway, NJ 08854-4141, http://www.ieee.org.
Available from BIPM, Sèvres Cedex, France, https://www.bipm.org.
Available from National Nuclear Data Center at Brookhaven National Laboratory, W Princeton Ave, Yaphank, NY 11980, http://www.nndc.bnl.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4785 − 20
3. Terminology
3.1 Definitions—Definitions: For definitions of terms used in this test method, refer to Terminology D1129.
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
3.1.2 For definitions of terms used in this standard relating to radiochemical analysis, refer to Terminology D7902.
4. Summary of Test Method
4.1 Sodium iodide is added as a carrier prior to performing any chemical separations. The samples undergo an oxidation-
reduction process to ensure exchange between the carrier and the radioactive iodide. Hydroxylamine hydrochloride and sodium
bisulfite are added to convert all the iodine to iodide which is then removed by anion exchange. Subsequent elution of the iodide
is followed by oxidation-reduction to elemental iodine. The elemental iodine is purified by solvent extraction, reduced to iodide,
and precipitated as cuprous iodide. The chemical recoveryyield is determined from the recovery net mass of therecovered iodide
carrier.
5. Significance and Use
5.1 This test method was developed for measuring low levels of radioactive iodine in water. The results of the test may be used
to determine if the concentration of several radioisotopes of iodine in the sample exceeds the regulatory statuteslimits for drinking
water. With a suitable counting technique,techniques, sample size, and counting time, a detection limit of less than 0.037 Bq/L (1
pCi/L) is attainable by gamma-ray spectroscopy. This method was tested for spectrometry. I . Other iodine radioisotopes should
behave in an identical manner in this procedure. However, other iodine radioisotopes have not been tested according to Practice
D2777. The user of this method is responsible for determining applicability, bias, and precision for the measurement of other iodine
radioisotopes using this method.
5.2 This procedure addresses test method is intended for the analysis of iodine radioisotopes with half-lives greater than 2 hours,
121 123 124 125 126 129 130 131 132 133 135
which include I, I, I, I, I, I, I, I, I, I, and I. The test method was tested according to Practice D2777
using only I. The user of this test method is responsible for determining applicability, bias, and precision for the measurement
of other iodine radioisotopes.
6. Interferences
6.1 Stable iodine in the sample will interfere with the chemical recoveryyield determination. One milligram of ambient iodine
would produce a bias of about −4 %.–4 %.
6.2 There are numerous characteristic iodine X-rays at and below 33.6 keV which are indicative of iodine, but not of a specific
radioisotope of iodine. It is recommended that only discreet Only use discrete gamma energy lines at and above 35.5 keV be used
for identification and quantification of iodine radioisotopes.
7. Apparatus
7.1 Analytical Balance, readable to 0.1 mg.
7.2 Flexible Polyvinyl Chloride (PVC) Tubing, 6.35 mm ( ⁄4 in.) outside diameter, 1-m 1 m length.
7.3 Gamma-Ray Spectrometry System—High resolution gamma spectrometer (high purity germanium or equivalent) with a
useful energy range of approximately 30 keV to 1800 keV (see Practice D3649). and Practice D7282, Sections 8, and 9.2).
7.4 Glass Fiber Filter Paper, 11.5-cm 11.5 cm diameter.
7.5 Ion Exchange Column, glass tube, 35 6 2-mm 2 mm inside diameter, 150-mm 150 mm length, fitted with No. 8 one-hole
rubber stoppers and perforated disk.
7.6 Membrane Filters, 0.4 or 0.45-μm pore size, 25-mm 0.45 μm (or 0.4 μm) pore size, 25 mm diameter, with suitable filter
holder and vacuum filter flask.
7.7 Peristaltic Tubing Pump, variable speed, fitted with vinyl or silicone tubing.
7.8 pH Meter.
7.9 Sintered Glass Filter, Büchner funnel, 150-mL 150 mL size, medium or coarse porosity with suitable one-hole stopper and
vacuum filter flask.
7.10 Vacuum Desiccator.
7.11 Vortex Mixer.
D4785 − 20
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society. Other
grades may be used provided they are of sufficiently high purity to permit their use without reducing the accuracy of the
determination. Some reagents, even those of high purity, may contain naturally-occurring radioactivity, such as isotopes of
uranium, radium, actinium, thorium, rare earths, potassium compounds, or artificially produced radionuclides, or combinations
thereof. Consequently, when such reagents are used in the analysis of low-radioactivity samples, the activity of the reagents should
be determined under analytical conditions that are as close as practicable to those used for the test sample. The activity contributed
by the reagents should be accounted for and applied as a correction when calculating the test sample result.
8.2 Purity of Water—Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to
Specification D1193, Type III.
8.3 Radioactive Purity—Radioactive purity shall be such that the measured radioactivity of blank samples does not exceed the
calculated probable error of the measurement.
8.3 Ammonium Hydroxide (sp gr 0.90)—Concentrated ammonium hydroxide (NH OH).
8.4 Ammonium Hydroxide (1.4 M)—Mix one volume of concentrated NH OH (sp gr 0.90) with nine volumes of water.
8.5 Anion Exchange Resin—Strongly basic, styrene, quarternaryquaternary ammonium salt, 20–50 mesh, chloride form,
Dowex 1-X8, or equivalent.
8.6 Cuprous Chloride Solution (approximately 10 mg CuCl/mL)—Dissolve 10 g of CuCl (99.99 %) in 26 mL of concentrated
HCl (sp gr 1.19). Add this solution to 1000 mL of NaCl solution (1 M) slowly with continuous stirring. Add a small quantity of
metallic copper (for example, 5 to 10 copper metal shot) to the solution for stabilization. Store the CuCl salt in a desiccator.
8.7 Hydrochloric Acid (sp gr 1.19)—Concentrated hydrochloric acid (HCl).
8.8 Hydrochloric Acid Solution (0.3 M)—Dilute 25 mL of concentrated HCl to 1000 mL with water.
8.9 Hydroxylamine Hydrochloride (NH OH:HCl)—Crystals.
8.10 Iodide Carrier Solution (25 mg I/mL)—Dissolve 14.76 g of NaI in approximately 80 mL of water in a 500-mL volumetric
flask and dilute to volume. Standardize using the procedure in Section 10.
8.11 Iodine-131 StandardizingStandard Solution—National standardizing body Solution traceable to the SI through a national
metrology institute (NMI), such as National Institute of Standards and Technology (NIST), traceable solution with a typical
concentration range from 1 to 10 kBq/mL.kBq/mL
8.12 Nitric Acid (sp gr 1.42)—Concentrated HNO .
8.13 Nitric Acid (1.4 M)—Mix 1 volume of concentrated HNO (sp gr 1.42) with 10 volumes of water.
8.14 Sodium Bisulfite Solution, (2 M)—Dissolve 104.06 g of NaHSO in approximately 300 mL of water in a 500-mL
volumetric flask and dilute to volume.
8.15 Sodium Chloride Solution (1 M)—Dissolve 58.45 g of NaCl in approximately 500 mL of water in a 1000 mL volumetric
flask and dilute to volume.
8.16 Sodium Hydroxide Solution (12.5 M)—Dissolve 500 g of NaOH in 800 mL of water and dilute to 1 L. (Warning—The
dissolution of sodium hydroxide may produce excessive heat.)
8.17 Sodium Hypochlorite (NaOCl)—Approximately 5 to 6 %. Commercially available bleach is acceptable. (Warning—
Acidification of NaOCl produces toxic chlorine gas and must be handled in a fume hood.)
8.18 Toluene. (Warning—Toluene is a carcinogen and must be handled and disposed of in an approved manner.)
125 129 131
8.19 Calibration Standard(s)—Known Use known amounts of of I, I, and I are used for calibration when determining
241 109 57 141 113 137 88
these radionuclides. A mixed-gamma standard, for example, standard containing Am, Cd, Co, Ce, Sn, Cs, Y,
and Co, is Co may be used for calibration over an extended energy range as required for the determination of additional
radioisotopes of iodine. TheseThe standards should be mounted on the filter as described (described in 7.6. The known amounts
of the radionuclides must be traceable to a national standardizing body such as NIST in the USA. The standard ) in a configuration
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, DC. For Suggestionssuggestions on the testing of reagents not listed by the American Chemical Society, see
AnnualAnalar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial
Convention, Inc. (USPC), Rockville, MD.
Dowex is a trademark of Dow Chemical Company, Midland, MI.
+2
CuCl solution is not stable. It can be oxidized to the Cu state by air after a period of time, when the solution will turn dark green. If this happens, prepare a fresh solution.
The shelf life of the solution can be extended by displacing the air over the remaining solution with nitrogen or argon gas after each use and then closing the container
promptly.
D4785 − 20
that closely matches that of sample test sources (STS) to be counted. Calibration standards may be prepared by the laboratory
performing this test method or by a commercial supplier of such standards. The standards used must be traceable to the SI through
an NMI. Standards obtained from ANSI N42.22 reference material providers will meet this requirement. Alternate radionuclides
may be used for calibration provided that they have gamma ray energies coveringthe calibration source covers gamma-ray energies
spanning the range of interest for the iodine radionuclides to be analyzed.
9. Hazards
9.1 Due to the potential health and safety effects from handling these compounds, the steps utilizing NaOCl and toluene must
be carried out in a fume hood. Toluene is a carcinogenhighly flammable and acidification of NaOCl liberates toxic Cl gas.
10. Standardization of Iodide Carrier
10.1 Pipet 1.0 mL of iodide carrier reagent into each of five 100-mL 100 mL centrifuge tubes containing 50 mL of deionized
water.
10.2 Add 0.1 mL of 2 M NaHSO to each solution and stir vigorously using a vortex mixer. Add 5.0 mL of freshly prepared
CuCl solution.
NOTE 1—A sixth standard prepared in parallel to the five replicates may be used to determine how much HCl or NH OH needs to be added to adjust
the pH to the range of 2.40–2.50.
10.3 Using a pH meter, check the pH of each solution and adjust the pH to between 2.40 to 2.50 with 0.3 M HCl or 1.4 M
NH OH.
10.4 Place each solution in a warm (approximately 50 to 60°C) water bath for 5 to 10 min, stirring occasionally.
10.5 Rinse each CuI precipitate onto a separate preweighed 0.45-μm membrane filter mounted in a vacuum filtration assembly.
Rinse the walls of the filter holder with approximately 50 mL of water.
10.6 Dry all samples in a vacuum desiccator for a minimum of 60 min or to constant weight. Remove and weigh the filter and
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 standard weight. The relative standard deviation of the mean should not exceed
0.025.
11. Calibration of High-Resolution Gamma-Ray Spectroscopy System
11.1 Accumulate an energy spectrum using a spectrum for calibration by counting the calibration standard (8.208.19) traceable
to a national standards body, in the geometrical position representing in a geometry matching that of the samplesSTS to be
analyzed. Accumulate sufficient net counts (total counts minus the Compton baseline) in each full-energy gamma-ray peak of
interest to obtain a relative standard counting uncertainty of ≤1 %.
11.2 Using the gamma-ray emission data from the calibration standard and the peak centroid location data from the calibration
spectrum, establish the energy per channel relationship (energy calibration) as:
Using the gamma-ray emission data from the calibration standard and the peak location data from the calibration spectrum,
establish the energy per channel relationship (energy calibration) as:
En 5 Offset1 Ch 3Slope (1)
~ !
where:
En = peak energy (keV),
Offset = energy offset for the energy calibration equation (keV),
Ch = peak location channel number, and
Slope = energy calibration equation slope (keV per channel).
NOTE 2—Most modern spectroscopyspectrometry software packages perform this calculation, and may include higher-order polynomial terms to
account for minor non-linearity in the energy calibration.
11.3 Using the gamma emission data from the calibration standard and the peak resolution data from the calibration spectrum,
establish the resolution versus energy relationship (peak-resolution calibration) as:
Using the gamma emission data from the calibration standard and the peak resolution data from the calibration spectrum,
establish the resolution versus energy relationship (energy calibration) as:
FWHM 5 Offset1 Ch 3Slope (2)
~ !
where:
FWHM = full width of the peak at one-half the maximum counts in the centroid channel (keV),
Offset = width offset for the resolution calibration equation (keV),
D4785 − 20
Offset = FWHM offset for the resolution calibration equation (keV),
En = peak centroid energy (keV), and
Slope = peak resolution calibration equation slope (keV/keV).
NOTE 3—Most modern spectroscopyspectrometry software packages perform this calculation, and may include higher-order polynomial terms to
account for non-linearity in the resolution calibration.
11.4 Using the gamma-ray emission data from the calibration standard, calculate the full-energy peak efficiency, ε , as follows:
f
For each gamma-ray photopeak, calculate the full-energy peak efficiency, ε , as follows:
f
R
n
ϵ 5 (3)
f
R 3DF
γ
R
n
ε 5 (3)
f
R 3DF
γ
where:
ε = full-energy peak efficiency (counts per gamma ray emitted),
f
–1
R = net gamma-ray count rate in the full-energy peak of interest, counts per second (s ),
n
–1
R = gamma-ray emission rate, in gamma-rays per second (s ), as of the reference date and time of the calibration standard,
γ
–λ(t –t
1 0
DF = decay factor for the calibrating radionuclide, e ),
–λ(t – t )
1 0
DF = decay factor for the calibrating radionuclide, e ,
λ = (ln 2) / t ,
1/2
t = half-life of calibrating radionuclide (half-life unit must match that used for the time difference, t – t ),
1/2 1 0
t = reference date and time of the calibration standard, and
t = midpoint of sample count (date and time).
11.5 Many modern Modern spectrometry systems are computerized and the determination of the calculate gamma-ray detection
efficiencies is performed automatically at the end of an appropriate counting interval. automatically. Refer to the manufacturer
instructions for specific requirements and capabilities.
11.6 Plot the values for the full-energy peak efficiency (as determined in Section 11.5) versus gamma-ray energy. Compare the
efficiency curve to the typical efficiency curve typical for the detector type. The curve should be smooth, continuous and have a
shape similar to the that reflects the type of detector being used. The plot will allow the determination of efficiencies at energies
throughout the range of the calibration energies and will show that the algorithms used in computerized systems are providing valid
efficiency calibrations. Select the fit that has the best 95 % confidence limit around the fitted curve, has all data points within 68 %
of the value of the fitted curve, or both. This is accomplished by calculating the biasdifference between the actual efficiency and
the efficiency calculated withusing the fitted curve.
11.7 Save or store the values of energy versus efficiency for future reference, to be used in the calculation of activity for each
iodine nuclide in Section 14.
12. Sampling
12.1 Collect a sample in accordance with PracticePractices D3370, Guide D4448, Guide D6001, or other approved procedure.
13. Procedure
13.1 Sample Preparation:
13.1.1 Measure or weigh 4 L of the sample into a suitable plastic container. While stirring, add 1.0 mL of iodide carrier and
5.0 mL of 5 to 6 % NaOCl. Stir approximately 3 to 5 min.
13.1.2 Add 2.0 g of NH OH:HCl, stir, and add 5.0 mL of 2 M NaHSO . Adjust the pH to 6.5 using 12.5 M NaOH or 1.4 M
2 3
HNO . Stir for 30 min.
13.1.3 Filter the sample through a glass fiber glass-fiber filter and discard the residue.
D4785 − 20
13.2 Anion Exchange Separation:
13.2.1 Slurry 100 mL (wet volume) of washed anion exchange resin into a 35 mm inside diameter inside-diameter glass column
fitted at the lower end with a one-hole rubber stopper, perforated disk, and a short length of 5 mm glass tubing connecting to the
inlet side of the peristaltic pump (see Fig. 1).
NOTE 4—The resin should be washed Wash the resin with water until the wash water shows no change in pH. This is most conveniently done by batch
sequential washing of a relatively large quantity of resin and storing the washed resin as a slurry.
13.2.2 Leave approximately 25 mL of water on top of the resin bed and insert a glass wool plug, being careful not to touch the
resin. Place a one-hole rubber stopper,stopper fitted with a short length of 5-mm 5 mm glass tubing, in the top of the column and
connect it to a 1-m 1 m length of flexible PVC tubing.
NOTE 5—If a peristaltic pump is not available, the sample can be passed through the column by gravity flow using an appropriate reservoir.
13.2.3 Pump approximately 100 mL of water through the resin-packed column and check the final effluent pH with pH paper.
Repeat the wash if the test indicates residual activity. acidity in excess of levels observed during the initial resin washes. Be sure
to leave approximately 25 mL of water standing on top of the resin bed in the glass column or be certain that the feed tube remains
full of water in order to prevent air from entering the resin bed before the sample reaches the column.
13.2.4 Place the flexible PVC inlet tube into the sample container. It may be desirable to attach a 250 to 300-mm 300 mm length
of glass tubing to the sample container end of the PVC to facilitate removal of the sample from the container.
13.2.5 Place the pump discharge tube into a beaker or bottle to collect the column effluent.
13.2.6 Start the pump and varyadjust the speed control to give a flow rate of 40 mL/min.
NOTE 6—It is necessary to calibrate Calibrate the variable speed control of the peristaltic pump by timing the flow of known liquid quantities at each
setting of the control.
13.2.7 When the sample container is empty, remove the upper stopper,stopper and glass wool plug from the top of the column
and pour the resin into a 600-mL 600 mL beaker.
13.2.8 Wash the resin with three successive 100-mL 100 mL portions of water. Stir briefly and allow the resin to settle to the
bottom of the beaker. Decant and discard the wash water.
13.2.9 Place a magnetic stirring bar in the beaker with the washed resin and add 250 mL of 5 to 6 % NaOCl. Place the beaker
on a magnetic stirrer and stir for 10 min. Allow the resin to settle. Filter the NaOCl solution by suction through a glass fiber
glass-fiber filter supported in a sintered glass Büchner-type funnel. Save the filtrate.
13.2.10 Add 250 mL of fresh 5 to 6 % NaOCl solution to the resin remaining in the beaker and stir for another 10 min. Allow
the resin to settle and filter the NaOCl solution into the Büchner funnel. Save the filtrate.
13.2.11 Add 50 mL of water solution to the resin remaining in the beaker and stir for 5 min. Filter the solution and resin into
the Büchner funnel and rinse the resin thoroughly with water. Save the filtrate. Transfer the NaOCl solution from this step, step
13.2.9, and 13.2.10 into a 2000-mL 2000 mL beaker and discard the resin. (Warning—Chlorine gas released. Acidification of the
residual NaOCl decomposes it, releasing chlorine gas (green color) which is highly toxic. This destroys residual NaOCl which
FIG. 1 Iodine Procedure: Ion Exchange
D4785 − 20
solution leads to decomposition of residual NaOCl that would interfere in the reduction of iodate to elemental iodine. All Highly
toxic chlorine gas is released (green color). Perform all subsequent steps through 13.2.16 are to be performed in a well-ventilated
fume hood.)
13.2.12 In an adequate fume hood, slowly add concentrated HNO (sp gr 1.42) to the NaOCl solution from 13.2.11 until the
pH is brought to 1. (Approximately 45 mL of HNO are required.) S
...