Designation: D 4785 – 08

Standard Test Method for

Low-Level Analysis of Iodine Radioisotopes in Water1

This standard is issued under the fixed designation D 4785; 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 (e) indicates an editorial change since the last revision or reapproval.

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 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 are provided for

information purposes only.

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 and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard

statements, see Note 2, Note 3, Note 9, and Section 9.

2. Referenced Documents

2.1 ASTM Standards: 2

D 1129 Terminology Relating to Water

D 1193 Specification for Reagent Water

D 2777 Practice for Determination of Precision and Bias of

Applicable Test Methods of Committee D19 on Water

D 3370 Practices for Sampling Water from Closed Conduits

D 3648 Practices for the Measurement of Radioactivity

D 3649 Practice for High-Resolution Gamma-Ray Spectrometry of Water

D 5847 Practice for Writing Quality Control Specifications

for Standard Test Methods for Water Analysis

D 3856 Guide for Good Laboratory Practices in Laboratories Engaged in Sampling and Analysis of Water

3. Terminology

3.1 Definitions—For definitions of terms used in this test

method, refer to Terminology D 1129.

4. Summary of Test Method

4.1 Sodium iodide is added as a carrier prior to performing

any chemical separations. The samples undergo an oxidationreduction 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 recovery is determined from the recovery of the

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 statutes for

drinking water. With a suitable counting technique, 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 131I . Other iodine radioisotopes should

behave in an identical manner in this procedure. However,

other iodine radioisotopes have not been tested according to

Practice D 2777. 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 the analysis of iodine radioisotopes with half-lives greater than 2 hours, which include

121I, 123I, 124I, 125I, 126I, 129I, 130I, 131I, 132I, 133I, and

135I.

6. Interferences

6.1 Stable iodine in the sample will interfere with the

chemical recovery determination. One milligram of ambient

iodine would produce a bias of about −4 %.

6.2 There are numerous characteristic iodine X-rays at and

below 33.6 keV which are indicative of iodine, but not a

specific radioisotope of iodine. It is recommended that only

discreet 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.

1 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 April 1, 2008. Published April 2008. Originally

approved in 1988. Last previous edition approved in 2000 as D 4785 – 00a. 2 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’s Document Summary page on

the ASTM website.

1

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
7.2 Flexible Polyvinyl Chloride (PVC) Tubing, 6.35 mm (1⁄4

in.) outside diameter, 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 D 3649).

7.4 Glass Fiber Filter Paper, 11.5-cm diameter.

7.5 Ion Exchange Column, glass tube, 35 6 2-mm inside

diameter, 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

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 size,

medium or coarse porosity with suitable one-hole stopper and

vacuum filter flask.

7.10 Vacuum Desiccator.

7.11 Vortex Mixer.

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.3

Other grades may be used provided they are of sufficiently high

purity to permit their use without reducing the accuracy of the

determination.

8.2 Purity of Water— Unless otherwise indicated, reference

to water shall be understood to mean reagent water conforming

to Specification D 1193, 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.

8.4 Ammonium Hydroxide (sp gr 0.90)—Concentrated ammonium hydroxide (NH4OH).

8.5 Ammonium Hydroxide (1.4 M)—Mix one volume of

concentrated NH4OH (sp gr 0.90) with nine volumes of water.

8.6 Anion Exchange Resin—Strongly basic, styrene, quarternary ammonium salt, 20–50 mesh, chloride form, Dowex

1-X8, or equivalent.

8.7 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.4 Store the CuCl in a

desiccator.

8.8 Hydrochloric Acid (sp gr 1.19)—Concentrated hydrochloric acid (HCl).

8.9 Hydrochloric Acid Solution (0.3 M)—Dilute 25 mL of

concentrated HCl to 1000 mL with water.

8.10 Hydroxylamine Hydrochloride (NH2OH:HCl)—

Crystals.

8.11 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.

8.12 Iodine-131 Standardizing Solution—National standardizing body such as National Institute of Standards and

Technology (NIST), traceable solution with a typical concentration 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 concentrated

HNO3 (sp gr 1.42) with 10 volumes of water.

8.15 Sodium Bisulfite Solution (2 M)—Dissolve 104.06 g

of NaHSO3 in approximately 300 mL of water in a 500-mL

volumetric flask and dilute to volume.

8.16 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.

8.17 Sodium Hydroxide Solution (12.5 M)—Dissolve 500 g

of NaOH in 800 mL of water and dilute to 1 L.

NOTE 1—Caution: The dissolution of sodium hydroxide may produce

excessive heat.

8.18 Sodium Hypochlorite (NaOCl)—Approximately 5 to

6 %. Commercially available bleach is acceptable.

NOTE 2—Warning: Acidification of NaOCl produces toxic chlorine

gas and must be handled in a fume hood.

8.19 Toluene.

NOTE 3—Warning: Toluene is a carcinogen and must be handled and

disposed of in an approved manner.

8.20 Calibration standard(s)—Known amounts of 125I, 129I,

and 131I are used for calibration when determining these

radionuclides. A mixed-gamma standard, for

example, 241Am, 109Cd, 57Co, 141Ce, 113Sn, 137Cs, 88Y,

and 60Co, is used for calibration over an extended energy range

as required for the determination of additional radioisotopes of

iodine. These standards should be mounted on the filter as

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 may be prepared by the laboratory

3 Reagent Chemicals, American Chemical Society Specifications, American

Chemical Society, Washington, DC. For suggestions on the testing of reagents not

listed by the American Chemical Society, see Analar 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.

4 CuCl solution is not stable. It can be oxidized to the Cu+2 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.

D 4785 – 08

2
performing this method or by a commercial supplier of such

standards. Alternate radionuclides may be used for calibration

provided that they have gamma ray energies covering the range

of interest for the iodine radionuclides to be analyzed.

9. Hazards

9.1 Due to the potential health effects from handling these

compounds, the steps utilizing NaOCl and toluene must be

carried out in a fume hood. Toluene is a carcinogen and

acidification of NaOCl liberates toxic Cl2 gas.

10. Standardization of Iodide Carrier

10.1 Pipet 1.0 mL of iodide carrier reagent into each of five

100-mL centrifuge tubes containing 50 mL of deionized water.

10.2 Add 0.1 mL of 2 M NaHSO3 to each solution and stir

vigorously using a vortex mixer. Add 5.0 mL of freshly

prepared CuCl solution.

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

NH4OH.

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 the calibration

standard (8.20) traceable to a national standards body, in the

geometrical position representing that of the samples 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 location data from the calibration

spectrum, establish the energy per channel relationship (energy

calibration) 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, and

Slope = energy calibration equation slope (keV per channel).

NOTE 4—Most modern spectroscopy 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

(energy calibration) as:

FWHM 5 Offset 1 ~Ch 3 Slope! (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),

En = peak energy (keV), and

Slope = resolution calibration equation slope (keV/keV).

NOTE 5—Most modern spectroscopy software packages perform this

calculation, and may include higher-order polynomial terms to account for

non-linearity in the resolution calibration.

11.4 For each gamma-ray photopeak, calculate the fullenergy peak efficiency, ef

, as follows:

ef 5 Rn

Rg 3 DF (3)

where:

ef = full-energy peak efficiency (counts per gamma ray

emitted),

Rn = net gamma-ray count rate in the full-energy peak of

interest, counts per second (s–1),

Rg = gamma-ray emission rate, in gamma-rays per second

(s–1), as of the reference date and time of the

calibration standard,

DF = decay factor for the calibrating radionuclide, e–l(t1 –

t0

),

l = (ln 2) / t1/2,

t1/2 = half-life of calibrating radionuclide (half-life unit

must match that used for the time difference, t1– t0),

t0 = reference date and time of the calibration standard,

and

t1 = midpoint of sample count (date and time).

11.5 Many modern spectrometry systems are computerized

and the determination of the gamma-ray detection efficiencies

is performed automatically at the end of an appropriate

counting interval. 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 for the

detector type. The curve should be smooth, continuous and

have a shape similar to the 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 bias between the actual

efficiency and the efficiency calculated with 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.

D 4785 – 08

3
12. Sampling

12.1 Collect a sample in accordance with Practice D 3370 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 NH2OH:HCl, stir, and add 5.0 mL of 2

M NaHSO3. Adjust the pH to 6.5 using 12.5 M NaOH or 1.4 M

HNO3. Stir for 30 min.

13.1.3 Filter the sample through a glass fiber filter and

discard the residue.

13.2 Anion Exchange Separation:

13.2.1 Slurry 100 mL (wet volume) of washed anion exchange resin into a 35 mm 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 6—The resin should be washed 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, fitted with a

short length of 5-mm glass tubing, in the top of the column and

connect it to a 1-m length of flexible PVC tubing.

NOTE 7—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. 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 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 vary the speed control to give a

flow rate of 40 mL/min.

NOTE 8—It is necessary to 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, and glass wool plug from the top of the column

and pour the resin into a 600-mL beaker.

13.2.8 Wash the resin with three successive 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 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 beaker and

discard the resin.

NOTE 9—Precaution: Chlorine Gas Released. Acidification of the

residual NaOCl decomposes it, releasing chlorine gas (green color) which

is highly toxic. This destroys residual NaOCl which would interfere in the

reduction of iodate to elemental iodine. 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

HNO3 (sp gr 1.42) to the NaOCl solution from 13.2.11 until the

pH is brought to 1. (Approximately 45 mL of HNO3 are

required.) Stir magnetically until the bulk of the chlorine gas

has evolved from the solution.

13.2.13 Pour the acidified solution into a 1000-mL separatory funnel containing 100 mL of toluene and 2 g of

NH2OH·HCl.

NOTE 10—Hydroxylamine hydrochloride is a mild reducing agent

capable of reducing iodate to iodine (I°). Iodine is preferentially soluble in

the toluene phase and can be separated by solvent extraction. When

NH2OH·HCl is added, some gas evolution will occur and the solution

color will darken (straw to amber) due to the formation of the complex

ions I3

−

(a combination of I2 and I−).

13.2.14 Shake the separatory funnel for a total of 2 min,

relieving the pressure occasionally. Allow the phases to separate. Drain off the lower aqueous phase into a second clean

1000-mL separatory funnel containing 2 g of hydroxylamine

FIG. 1 Iodine Procedure: Ion Exchange

D 4785 – 08

4
hydrochloride, and 100 mL of toluene. Allow a few drops of

the toluene to drain off with the aqueous phase. Save the

toluene in the first separatory funnel.

NOTE 11—It is necessary to relieve the pressure at the beginning of

shaking and a few times during the 2-min shaking. As the iodine transfers

to the toluene phase, the dark color of the aqueous phase will be replaced

by a violet color in the toluene due to dissolved elemental iodine.

13.2.15 Shake the second separatory funnel for 2 min,

relieving the pressure occasionally. Allow the phases to separate, and discard the lower aqueous phase (a third extraction

can be performed if desired). Combine this toluene with the

first toluene fraction in the first separatory funnel.

13.2.16 To the combined toluene in the separatory funnel,

add 50 mL of water containing 0.1 mL of 2 M NaHSO3. Shake

for 2 min. Allow the phases to separate and drain off the lower

aqueous phase into a 100-mL centrifuge tube until the toluene

phase enters the stopcock bore. Discard the toluene in an

appropriate hazardous waste container.

NOTE 12—The NaHSO3 reduces the iodine to iodide which is not

soluble in toluene. The color in the toluene fades rapidly as the iodine is

extracted into the aqueous phase. Remove any remaining toluene drops in

the centrifuge tube with a disposable transfer pipet.

13.3 CuI Precipitation and Mounting:

13.3.1 Add 5 mL of the CuCl solution and stir thoroughly.

Adjust the pH to between 2.40 to 2.50 with 0.3 M HCl or 1.4

M NH4OH solution as required.

NOTE 13—The proper pH during the CuI precipitation is crucial. A pH

of less than 2.4 causes incomplete iodide precipitation. A pH value of

greater than 2.6 will cause a yellow to green color to appear in the

precipitate and the coprecipitation of some form of the excess copper,

resulting in artificially high chemical recoveries.

13.3.2 Allow the precipitate to stand with occasional mixing

for 5 to 10 min.

NOTE 14—Paragraphs 13.3.3 through 13.3.6 presuppose that the radioactivity will be determined using gamma-ray spectrometry. Suitable

adjustments may be made if beta-gamma coincidence counting is used

(see Practice D 3648).

13.3.3 Mount a preweighed membrane filter (0.4 or 0.45-μm

pore size or equivalent) on a suction filtration apparatus and

filter the CuI precipitate. Wash the walls of the filter holder and

the precipitate with water.

13.3.4 Place the sample into the vacuum dessicator and dry

under vacuum for a minimum of 60 min or to constant weight.

Remove the sample, weigh it, and record the weight.

13.3.5 Mount the sample for counting in a reproducible

geometrical arrangement for which the gamma-ray spectrometry system has been, or will be, calibrated for detection

efficiency.

13.3.6 Using the high resolution gamma-ray spectrometry

system, determine the net counting rate for the gamma-ray

energy lines of each iodine nuclide to be assayed. Listed in

Table 1 are recommended gamma energy lines and gamma

TABLE 1 Nuclear Decay Data for Iodine Radioisotopes

Iodine Nuclide Gamma

Energy (keV)

Gamma

Fraction Half-Life

121I 212.2 0.843 127.2 min

532.08 0.0610 123I 158.97 0.833 13.27 h 124I 511 0.4616 4.176 d

602.72 0.605

722.78 0.0998

1691.02 0.1041 125I 35.49 0.06681 59.41 d 126I 388.63 0.340 13.11 d

666.33 0.331 129I 37.6 0.075 1.57 3 107 a 130I 418.01 0.342 12.36 h

536.09 0.99

668.54 0.996

739.48 0.820

1157.47 0.113 131I 284.3 0.0614 8.02 d

364.49 0.817

636.99 0.0717 132I 522.65 0.16 137.7 min

630.19 0.1330

667.72 0.987

772.6 0.756

812 0.0550

954.55 0.1760

1398.57 0.0701 133I 529.87 0.87 20.8 h

875.33 0.0451 135I 546.56 0.072 6.57 h

836.8 0.0673

1038.76 0.0801

1131.51 0.2274

1260.41 0.289

1457.56 0.0873

1678.03 0.0962

1791.2 0.0777

D 4785 – 08

5
emission fractions obtained from the National Nuclear Data

Center.5

14. Calculation

NOTE 15—The following calculations assume that there are no interfering photopeaks in the background or sample spectrum, and none of the

iodine photopeaks are found in multiplets.

14.1 For each photopeak the net count rate, Rnet, and its

standard uncertainty, u(Rnet), are given by the following

equations:

Rnet 5 Rp – SRb 3 np

nb

D 5 Cp – ~Cb 3 np / nb!

ts

(4)

u~Rnet! 5 =Cp 1 ~Cb 3 np

2 / nb2!

ts

(5)

where:

Rp = photopeak count rate (s−1),

Rb = Compton baseline count rate (s−1),

Cp = total photopeak counts,

Cb = total Compton baseline counts,

ts = sample count time (s−1),

np = number of channels in the photopeak, and

nb = number of channels used in the baseline measurement.

14.2 When only one photopeak is used in the measurement

(for example, the 364 keV photopeak of 131I), the activity

concentration, AC, is given by:

AC 5 Rnet

ef 3 Ig 3 V 3 Y 3 e

–lt (6)

where:

Rnet = net count rate for the photopeak of interest (Eq 4),

ef = absolute detection efficiency of the gamma-ray

spectrometer for the photopeak of interest (Eq 3),

l = decay constant for the iodine isotope of interest,

equal to (ln 2) / t1/2, where the half-life, t1/2, comes

from Table 1,

t = elapsed time from sample collection to midpoint of

the sample counting period, in days,

V = volume of sample aliquant (L),

Y = fraction of the total iodine carrier recovered from

the sample, which is the weight of the sample

determined in 13.3 divided by the weight of standardized carrier in accordance with 10.8,

Ig = gamma-ray emission probability from Table 1.

14.3 When Eq 6 is used to calculate AC, the standard

counting uncertainty of AC (uncertainty due to counting

statistics only) is given by:

ucC~AC! 5 u~Rnet!

ef 3 Ig 3 V 3 Y 3 e

–lt (7)

where u (Rnet) comes from Eq 5.

14.4 Calculate the combined standard uncertainty of AC as

follows:

uc~AC! 5 =ucC

2 ~AC! 1 AC2 3 ~ur2

~ef! 1 ur

2

~Ig! 1 ur

2

~V! 1 ur

2

~Y! 1 ur

2

~...!

(8)

where:

ucC

2

(AC) = standard counting uncertainty of AC, from Eq

7,

ur (·) = relative standard uncertainty of the measured

quantity in parentheses,

ur (...) = relative standard uncertainty due to other

causes identified by the user.

14.5 Expanded Uncertainty (U):

The combined standard uncertainty, uc (AC), may be multiplied by a coverage factor, k, to obtain an expanded uncertainty, U.

U 5 k 3 uc~AC! (9)

The coverage factor k = 2 is often used. Assuming the

measurement process produces normally distributed results,

this coverage factor gives a coverage interval, AC 6 U, with a

coverage probability of approximately 95 %.

14.6 Calculate the critical activity concentration (LC) for

each sample measurement as follows:

LC 5

1.645ŒRb

ts

3 ~F 1 F2

!

ef 3 Ig 3 V 3 Y 3 e

–lt

(10)

where F=np/nb, and the other symbols are as defined above.

To decide whether the iodine isotope of interest is clearly

present in the sample, compare the measured activity concentration, AC, to LC.

14.7

NOTE 16—The following calculation for MDC requires the determination of the background area. Most automated gamma-ray software

performs this calculation using a similar equation. If the software does not

provide this calculation, the MDC calculation may be performed manually

using a printout of channel contents.

When the detection criterion of 14.6 is used, the a priori

minimum detectable activity concentration (MDC) may be

calculated as follows:

MDC 5 2.71 1 3.29=Rb 3 ts 3 ~F 1 F2

!

ts 3 ef 3 Ig 3 V 3 Y 3 e

–lt (11)

15. Quality Control

15.1 In order to provide reasonable assurance that the

analytical results obtained using this test method are valid and

accurate within the confidence limits of the method, Quality

Control (QC) samples are analyzed with each batch of samples

undergoing analysis. Each batch should include not more than

20 samples excluding those used for QC purposes. Laboratory

or project quality assurance plans may contain more restrictive

process QC requirements. The following minimum QC procedures must be followed when running the test method:

15.2 Internal Standard:

15.2.1 As indicated in 13.1.1, an accurately added amount

of stable iodide is used as a carrier in the determination of

radioiodine in the sample.

15.2.2 The recovery of the stable iodide carrier will be

calculated for each sample and associated QC samples. This

recovery should be reported along with the reported analytical

data. The relative standard uncertainty of the carrier recovery

measurement should be less than 5 %. As noted in Section

5 National Nuclear Data Center, Information extracted from NUDAT Data Base,

available at: http://www.nndc.bnl.gov/nudat2.

D 4785 – 08

6
10.8, the relative standard deviation of the mean of the five

calibration samples shall not exceed 0.025.

15.3 Calibration and Calibration Verification:

15.3.1 Standards used in the method shall be traceable to a

national standards laboratory (such as NIST or NPL).

15.3.2 The detector counting efficiency should be determined using at least three standards as noted in Section 11.

15.3.3 The detector efficiency shall be verified on a daily

basis or prior to use.

15.4 Initial Demonstration of Laboratory/Instrument/

Analyst Capability:

15.4.1 If a laboratory or analyst has not performed this test

before or there has been a major change in the measurement

system, for example, significant instrument change, new instrument, etc., a precision and bias study must be performed to

demonstrate laboratory, analyst, or instrument capability. A

significant change is defined as any change, repair, or alteration

of any component in the system, which may be expected to

affect the response of the measurement system.

15.4.2 Analyze seven replicates of a standard solution

prepared from a independent reference material (IRM) containing iodine-131 activity sufficient to reduce counting uncertainty to 1 % or less at one sigma. The matrix used for the

demonstration should represent a water sample typical for

which the method will be used, for example, a surface water.

The total dissolved solids (TDS) of the matrix should approximate that which may be encountered in normal use. In addition

interference radioisotopes should be included in the matrix

because they can interfere in the determination of the radioisotope of interest. The interference radioisotopes should be

included at a level of at least ten times the a priori MDC of the

analysis.

15.4.3 Calculate the mean and standard deviation of the

seven values and compare to the acceptable ranges of precision

and mean bias of 10 % and 615 %, respectively, based on a

review of the collaborative study data. Test Method D 5847

should be consulted on the manner by which precision and

mean bias are determined from the initial demonstration study.

The study should be repeated until the precision and bias are

within the given limits.

15.4.4 Analyze three replicates of a blank (in 131I) solution

matrix. The matrix used for the demonstration should represent

a water sample typical for which the method will be used, for

example, surface water. The total dissolved solids (TDS) of the

matrix should approximate that which may be encountered in

normal use. In addition interference isotope or isotopes should

be included in the matrix because they can interfere in the

determination of radioisotope of interest. The interference

radioisotopes should be included at a level of at least five times

the a priori MDC of the analysis.

15.4.5 Calculate the iodine-131 activity for each of these

three blank solutions. This study should be repeated until the

iodine-131 result of each of the three blank solutions is below

half the associated MDC for each of the analytes.

15.4.6 This method shall not be used for official samples

until precision, bias, and blank requirements are met.

15.5 Laboratory Control Sample (LCS):

15.5.1 To ensure that the test method is within control

limits, analyze an LCS with each batch of no more than 20

samples. The activity added to reagent water should be

appropriate for the type of samples analyzed and allow

sufficient precision to ensure a meaningful assessment of

accuracy. The LCS must be taken through all the steps of the

analytical method including sample preservation and pretreatment. The result obtained for the LCS should fall within the

limit of 625 % of the expected value.

15.6 Method Blank:

15.6.1 Analyze a reagent water test blank with each batch of

no more than 20 samples. The concentration of analytes found

in the blank should be less than half the MDC of the analytes

of interest. If the concentration of the analytes is found above

this level, provide an explanation in a case narrative. If the

result is not within the limit, analyses should be stopped and

the reason for the failure should be identified and resolved.

15.7 Matrix Spike:

15.7.1 Analyze at least one matrix spike sample with each

batch of no more than 20 samples by spiking an aliquot of a

sample within the batch with a known concentration of

radioiodine.

15.7.2 The spike should produce a concentration that is 2 to

5 times the anticipated sample concentration or as specified by

the laboratory, whichever is greater.

15.7.3 The Matrix Spike must be taken through all the steps

of the method.

15.7.4 Calculate the percent recovery of the matrix spike (R)

using the following formula:

R 5 ACas – ACa

ACs

3 100 % (12)

where:

ACas = the concentration of analyte in becquerels per litre

(Bq/L) measured in the spiked aliquot,

ACa = the concentration of analyte in becquerels per litre

(Bq/L) in the sample, and

ACs = the spiked concentration of analyte in becquerels

per litre (Bq/L).

15.7.5 The percent recovery, R, should fall within 625 % of

the expected value. If the concentration is not within these

limits, provide an explanation in a case narrative.

15.8 Duplicate:

15.8.1 To check the precision of sample analyses, analyze a

sample in duplicate with each batch of no more than 20

samples. Calculate the statistical agreement (duplicate error

ratio (DER)) between the two results. This calculation is

performed using the combined standard uncertainty of each

result as shown below.

DER 5 | ACoriginal – ACdup |

=uc

2

~ACoriginal! 1 uc

2

~ACdup! (13)

where:

ACoriginal = original sample activity concentration,

ACdup = duplicate sample activity concentration,

uc(ACoriginal) = combined standard uncertainty of the

original sample, and

D 4785 – 08

7
uc(ACdup) = combined standard uncertainty of the duplicate sample.

15.8.2 In those cases where there is insufficient sample

volume to allow performance of a duplicate sample analysis, a

duplicate LCS (LCS-D) should be performed and analyzed

using the same DER criteria.

15.8.3 The value of DER should be less than or equal to 3.0.

If the sample duplicate or LCS duplicate result is not within

these limits all samples in the batch must be reanalyzed, or an

explanation must be provided in a case narrative.

15.9 Independent Reference Material (IRM):

15.9.1 In order to verify the quantitative value produced by

the test method, analyze an IRM sample, which was submitted

on at least a single-blind basis (if practical) to the laboratory at

least once per quarter. The concentration of analyte in the

traceable reference material should be appropriate to the

typical purpose for which the method is used. The value

obtained shall demonstrate acceptable performance as defined

by the program or the outside source.

15.9.2 In the absence of other acceptance criteria for the

IRM sample, compare the IRM sample result to the IRM

known value as follows:

R 5 | IRMfound – IRMknown |

=uc

2

~IRMfound! 1 uc

2

~IRMknown! (14)

where:

R = relative difference,

IRMfound = found concentration of the IRM,

IRMknown = known concentration of the IRM,

uc(IRMfound) = combined standard uncertainty of the

IRM found concentration, and

uc(IRMknown) = combined standard uncertainty of the

IRM known concentration.

15.9.3 The value of R should be less than or equal to 3.0. If

the value of R is greater than 3.0, the method should be

investigated to determine the cause.

16. Precision and Bias 6

16.1 The collaborative test conducted of this test method

included 6 laboratories each with one operator. Three activity

levels of 131I between 0.74 Bq/L (20 pCi/L) and 149 Bq/L

(4020 pCi/L) were tested with three replicates per level. The

determinations of the precision and bias statements were made

in accordance with Practice D 2777.

16.2 These collaborative test data were obtained using

reagent grade water.

16.3 The overall precision S(T) and single-operator precision

S(O) have been found to vary with level in a manner according

to Fig. 2.

16.4 The bias of this test method, based upon the collaborative test data, was found to vary with level according to Table

2.

17. Keywords

17.1 iodine; ion exchange; low-level activity; radioiodine;

radioactivity; solvent extraction water

6 Supporting data have been filed at ASTM International Headquarters and may

be obtained by requesting Research Report RR: D19-1136.

FIG. 2 S (T) and S (o) versus Concentration

D 4785 – 08

8
ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned

in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk

of infringement of such rights, are entirely their own responsibility.

This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and

if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards

and should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the

responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should

make your views known to the ASTM Committee on Standards, at the address shown below.

This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,

United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above

address or at 610-832-9585 (phone), 610-832-9555 (fax), or service@astm.org (e-mail); or through the ASTM website

(www.astm.org).

TABLE 2 131I Precision and Bias Data A

Amount Added Amount Found Relative

Bias

(%)

Relative

Precision (%)

Bq/L pCi/L Bq/L pCi/L

0.74 6 0.01 20.2 6 0.4 0.78 6 0.12 21.1 6 3.1 4.4 14.7

30 6 1 809 6 17 29.6 6 4.0 802 6 94 − 0.8 11.7

149 6 9 4020 6 82 152 6 16 4100 6 426 1.9 10.4

A For the 0.74-Bq/L (20-pCi/L) sample, the random uncertainty associated with

counting statistics ranged up to 10 % at the 2-sigma level.

D 4785 – 08

9