7500-I RADIOACTIVE IODINE*
7500-I A. Introduction
1.
Occurrence and Significance
Radioiodine that results from testing nuclear devices or is
released during use and processing of reactor fuels is a major
concern in radioactivity monitoring. Fission products may con-
tain iodine-129 through iodine-135. Iodine-129 has a half-life of
1.6 ⫻10
7
years but a relatively low specific activity (1.73 ⫻
10
⫺4
Ci/g for
129
I as compared to 1.24 ⫻10
5
Ci/g for
131
I). The
half-life of
131
I is 8 d while for the other isotopes it is shorter
(35 min to 21 h). At present, only
131
I is likely to be found in
water. When ingested or inhaled, it concentrates in the thyroid
gland and may cause thyroid cancer.
2.
Selection of Method
Of the three methods, the precipitation method (B) is preferred
because it is simple and involves the least time. Method C, in which
iodide is concentrated by absorption on an anion resin, purified, and
counted in a beta-gamma coincidence system, is sensitive and
accurate. Method D uses distillation. With each method it is possi-
ble to reach the EPA recommended detection limit of 1 pCi
131
I/L.
3. Bibliography
KLEINBERG, J. & G.A. COWAN. 1960. The Radiochemistry of Fluorine,
Chlorine, Bromine and Iodine. Rep. NAS-NS-3005, U.S. Atomic
Energy Comm.
BRAUER, F.P., J.H. KAYE & R.E. CONNALY. 1970. X-ray and

-
␥
.
Coincidence Spectrometry Applied to Radiochemical Analysis
of Environmental Samples. Advances in Chemistry Ser., No. 93,
Radionuclides in the Environment, pp. 231–253. American
Chemical Soc.
7500-I B. Precipitation Method
1.
General Discussion
a. Principle: Iodate carrier is added to an acidified sample and,
after reduction with Na
2
SO
3
to iodide, the
131
I is precipitated
with AgNO
3
. The precipitate is dissolved and purified with zinc
powder and H
2
SO
4
and the solution is reprecipitated as PdI
2
for
counting.
b. Quality control (QC): The QC practices considered to be an
integral part of each method can be found in Section 7020.
2.
Apparatus
a. Counting instrument: Low-background beta counter (see
Section 7030B.1) or gamma spectrometer (Section 7030B.5).
b. Fine-fritted glass funnel.
c. Filter apparatus: Two-piece filter funnel with filtering
equipment.*
d. Filter materials: Filter paper;† glass-fiber filter, 2.4 cm
diam; or 0.8-
m pore-diam membrane filter, 4.7 cm diam.
3.
Reagents
a. Ammonium hydroxide, NH
4
OH, 6N.
b. Ethanol, 95%.
c. Hydrochloric acid, HCl, 6N.
d. Iodate carrier: Dissolve 1.685 g KIO
3
in distilled water and
dilute to 100 mL. Store in dark flask; 1 mL ⫽10 mg I.
e. Nitric acid, HNO
3
, conc.
f. Palladium chloride, PdCl
2
: Dissolve 3.3 g PdCl
2
in 100 mL
6NHCl; 1 mL ⫽20 mg Pd.
g. Silver nitrate, AgNO
3
, 0.1M: Dissolve 17 g AgNO
3
in
distilled water and dilute to 1000 mL. Store in dark flask.
h. Sodium sulfite, Na
2
SO
3
,1M(freshly prepared): Dissolve
6.3gNa
2
SO
3
in distilled water and dilute to 50 mL.
i. Sulfuric acid, H
2
SO
4
,2N.
j. Zinc, powder, reagent grade.
4.
Procedure
a. To a 2000-mL sample, add 15 mL conc HNO
3
and 1.0 mL
iodate carrier. Mix well. Add 4 mL freshly prepared 1MNa
2
SO
3
and stir for 30 min. Add 20 mL 0.1MAgNO
3
, stir for 1 h, and
let settle for 1 h. Decant and discard as much of the supernatant
as possible. Filter remainder through a glass-fiber filter and
discard filtrate.
b. Transfer filter to a centrifuge tube and slurry with 10 mL
distilled water. Add 1 g zinc powder and 2 mL 2NH
2
SO
4
and stir
frequently for at least 30 min. Filter, with vacuum, through a
fine-fritted glass funnel and collect filtrate in an erlenmeyer flask.
Wash both residue and filter with a minimum quantity of dis-
tilled water and add wash water to filtrate. Discard residue.
c. Add2mL6NHCl and heat in water bath at 80°C for
10 min. Add 1 mL 0.2MPdCl
2
and digest for at least 5 min.
Centrifuge and discard supernatant.
* Approved by Standard Methods Committee, 2000. Editorial revisions, 2011.
* Fisher Filtrator or equivalent.
† Whatman No. 42 or equivalent.
1
d. Dissolve precipitate in 5 mL 6NNH
4
OH and heat in boiling
water bath for 5 min. Filter through a glass-fiber filter and collect
filtrate in a centrifuge tube. Discard filter and residue.
e. Neutralize filtrate with 6NHCl, add 2 mL in excess, and
heat in a water bath. Add 1 mL 0.2MPdCl
2
to reprecipitate PdI
2
and digest for 10 min. Cool slightly and transfer to a tared filter
with distilled water. Wash successively with 5-mL portions of
distilled water and 95% ethanol. Dry in a vacuum oven at 60°C
for 1 h, weigh precipitate, mount, and beta-count.
f. If final PdI
2
precipitate on a glass-fiber filter is counted in a
low-background beta counter, the background counting rate is
relatively high (about 1.3 cpm). If precipitate is collected on a
0.8-
m membrane filter and dried for 30 min at 70°C it may be
counted in a beta-gamma coincidence scintillation system with a
background rate of less than 0.1 cpm.
If a low-background counter is used, confirm identity of
131
Iby
recounting precipitate after about 1 week to check the half-life.
5.
Calculation
Calculate concentration of radioiodine as follows:
131
I, pCi/L ⫽C
2.22 ⫻EVR ⫻A
where:
C⫽net count rate, cpm,
E⫽counting efficiency of
131
I as function of mass of PdI
2
precipitate,
V⫽volume of sample, L,
R⫽fractional chemical yield
⫽
recovered PdI
2
⫻0.0704
added iodine carrier , and
A⫽
131
I decay factor for the time interval between sample
collection and measurement.
6. Bibliography
U.S. ENVIRONMENTAL PROTECTION AGENCY. 1980. Prescribed Procedures
for Measurement of Radioactivity in Drinking Water. EPA-600/4-
80-032, Environmental Monitoring and Support Lab., Cincinnati,
Ohio.
7500-I C. Ion-Exchange Method
1.
General Discussion
a. Principle: A known amount of inactive iodine in the form
of KI is added as a carrier and the sample is taken through an
oxidation-reduction step using hydroxylamine and sodium bisul-
fite to convert all iodine to iodide. Iodine, as the iodide, is
concentrated by absorption on an anion-exchange column. Fol-
lowing an NaCl wash, iodine is eluted with sodium hypochlorite.
Iodine in the iodate form is reduced to I
2
, extracted into CCl
4
,
and back-extracted as iodide into water. The iodine finally is
precipitated as PdI
2
.
b. Quality control (QC): The QC practices considered to be an
integral part of each method can be found in Section 7020.
2.
Apparatus
a. Counting instrument: Low-background beta counter (Sec-
tion 7030B.1) or gamma spectrometer (Section 7030B.5).
b. Chromatographic column, 2cm⫻15 cm.
c. Vacuum filter holder, 2.5 cm
2
filter area.
d. Filter paper,* 2.4 cm diam.
e. Vacuum oven.
3.
Reagents
a. Iodine carrier: Weigh approximately 13 g dried KI to the
nearest 0.1 mg. Dissolve in a 1-L volumetric flask containing
100 mL distilled water. Add 10 mL 1MNaHSO
3
and dilute to
mark with distilled water. Concentration of carrier I, mg/L ⫽g
KI ⫻0.7644.
b. Ethanol, absolute.
c. Hydroxylamine hydrochloride, 1M: Dissolve 6.95 g
NH
2
OH 䡠HCl in distilled water and dilute to 100 mL.
d. Nitric acid, HNO
3
, conc, 8N, 1.6N.
e. Sodium bisulfite,1M: Dissolve 1.04 g NaHSO
3
in distilled
water and dilute to 10 mL.
f. Sodium hydroxide, 12N: Dissolve 480 g NaOH in distilled
water and dilute to 1 L.
g. Sodium hypochlorite, NaOCl, 5%: Use available household
bleach.
h. Anion-exchange resin.†
i. Carbon tetrachloride, CCl
4
, reagent grade.
j. Hydrochloric acid, HCl, 3N,1N.
k. Palladium chloride: Dissolve 3.3 g PdCl
2
in 100 mL 6N
HCl; 1 mL ⫽20 mg Pd.
l. Sodium chloride, NaCl, 2M: Dissolve 117 g NaCl in distilled
water and dilute to 1 L.
m. Hydroxylamine hydrochloride wash solution: Add 20 mL
conc HNO
3
and 20 mL 1MNH
2
OH 䡠HCl to 100 mL distilled
water.
4.
Procedure
a. To 1 L sample in a beaker add, while stirring, 2.0 mL iodine
carrier and 5 mL 5% NaOCl, and heat for 2 to 3 min to complete
oxidation. After the interchange reaction (2 to 3 min), slowly add
5 mL conc HNO
3
. Add 25 mL 1MNH
2
OH 䡠HCl and stir. Let
* Whatman No. 42 or equivalent. † Dowex 1 ⫻8, 50-100 mesh, chloride form, or equivalent.
RADIOACTIVE IODINE (7500-I)/Ion-Exchange Method
2
RADIOACTIVE IODINE (7500-I)/Ion-Exchange Method
reaction go on for a few seconds, add 10 mL 1MNaHSO
3
, and
adjust pH to 6.5 with 12NNaOH or 1.6NHNO
3
. Stir thoroughly
for a few minutes. (Stir samples containing a large amount of
organic material, such as muddy water, for 45 min.) Filter
through a glass-fiber filter to remove suspended matter. Discard
residue.
b. Pour 20 mL anion-exchange resin into a column and wash
sides down with distilled water. Pass sample through ion-
exchange column at a flow rate of 20 mL/min. Discard effluent.
Wash column with 200 mL distilled water and then with 100 mL
2MNaCl at a flow rate of 4 mL/min. Discard wash solutions.
c. Add 50 mL 5% NaOCl in 10- to 20-mL increments, stirring
the resin as needed to eliminate gas bubbles, and maintain a flow
rate of 2 mL/min. To the eluted volume of 50 to 60 mL, collected
in a beaker, carefully add 10 mL conc HNO
3
to make sample 2
to 3Nin HNO
3
and transfer to a separatory funnel. (Add acid
slowly with stirring until vigorous reaction subsides.)
d. Add 50 mL CCl
4
and 10 mL 1MNH
2
OH 䡠HCl. Extract
iodine into organic phase by shaking for about 2 min. Let phases
separate and transfer organic phase to another separatory funnel.
Add 25 mL CCl
4
and5mL1MNH
2
OH 䡠HCl to the first
separatory funnel and shake for 2 min. Combine organic phase
with the one obtained from the first extraction. Discard aqueous
phase. Add 20 mL NH
2
OH 䡠HCl wash solution to the organic
phase and shake for 2 min. Let phases separate and transfer
organic phase to a clean separatory funnel. Discard wash solu-
tion.
e. Add 25 mL distilled water and 10 drops 1MNaHSO
3
to
organic phase. Shake for 2 min, let phases separate, and discard
organic phase. Transfer aqueous phase to a beaker. Add 10 mL
3NHCl. Using a stirrer-hot plate, boil and stir the sample until
it evaporates to 10 to 15 mL or begins to turn yellow.
f. Add 1.0 mL PdCl
2
solution dropwise. Rinse sides of beaker
with 1NHCl and add sufficient 1NHCl to make a volume of
30 mL. Continue stirring until cool. Place beaker in a stainless
steel tray and store at about 4°C overnight.
g. Filter through a tared filter mounted in a filter holder. Wash
residue with 1NHCl and then with absolute alcohol. Dry in a
vacuum oven at 60°C for 1 h. Cool in a desiccator, weigh
precipitate, then seal it between polyester tape and polyester
plastic film,‡ with the film over the precipitate. Count with a
beta-gamma coincidence system.
5.
Calculation
Calculate
131
I, pCi/L, as in 7500-I.B.5.
6. Bibliography
AMERICAN SOCIETY FOR TESTING AND MATERIALS. 1972 Book of ASTM
Standards. Part 23. D 2334-68, American Soc. Testing & Materials,
Philadelphia, Pa.
GABAY, J.J., C.J. PAPERIELLO,S.GOODYEAR, J.C. DALY & J.M. MATUSZEK.
1974. A method of determining
129
I in milk and water. Health Phys.
26:89.
7500-I D. Distillation Method
1.
General Discussion
a. Principle: Iodine carrier is added to an acidified sample and
iodine is distilled into a caustic solution. The distillate is acidi-
fied and the iodine is extracted into CCl
4
. After back-extraction
as iodide, the iodine is purified as PdI
2
for counting.
b. Quality control (QC): The QC practices considered to be an
integral part of each method can be found in Section 7020.
2.
Apparatus
a. Distillation apparatus and 3-L round-bottom flask.
b. Separatory funnel, 60 mL.
c. Filter apparatus: Two-piece filter funnel with filtering
equipment.*
d. Filter paper: See 7500-I.B.2d.
3.
Reagents
a. Ammonium hydroxide, NH
4
OH, conc.
b. Carbon tetrachloride, CCl
4
.
c. Ethanol, 95%.
d. Hydrochloric acid, HCl, 6N,1N.
e. Iodide carrier: Dissolve 2.616 g KI in distilled water, add
2 drops NaHSO
3
, and dilute to 100 mL. Store in dark flask. 1 mL
⫽20 mg I.
f. Nitric acid, HNO
3
, conc.
g. Palladium chloride: Dissolve 3.3 g PdCl
2
in 100 mL 6N
HCl; 1 mL ⫽20 mg Pd.
h. Sodium bisulfite, NaHSO
3
,1M: Dissolve 5.2 g NaHSO
3
in
distilled water and dilute to 50 mL. Prepare only in small quantities.
i. Sodium hydroxide, NaOH, 0.5N.
j. Sodium nitrite, NaNO
2
,1M: Dissolve 69 g NaNO
2
in
distilled water and dilute to 1 L.
k. Sulfuric acid, H
2
SO
4
,12N.
l. Tartaric acid, C
4
H
6
O
6
, 50%: Dissolve 50 g C
4
H
6
O
6
in
distilled water and dilute to 100 mL.
4.
Procedure
a. To a 2000-mL sample in a 3-L round-bottom flask, add
15 mL 50% C
4
H
6
O
6
and 1.0 mL iodide carrier. Mix well,
cautiously add 25 mL cold conc HNO
3
, and close distillation
apparatus (Figure 7500-I:1).
‡ Mylar, or equivalent.
* Fisher Filtrator, or equivalent.
RADIOACTIVE IODINE (7500-I)/Distillation Method
3
RADIOACTIVE IODINE (7500-I)/Distillation Method
b. Connect an air line to still inlet, adjust flow rate to about
2 bubbles/s, and distill for at least 15 min into 15 mL 0.5N
NaOH. Cool and transfer NaOH solution to a 60-mL separatory
funnel. Discard still residue.
c. Adjust distillate to slightly acid with 1 mL 12NH
2
SO
4
and
oxidize with 1 mL 1MNaNO
2
. Add 10 mL CCl
4
and shake for
1 to 2 min. Transfer organic layer to a clean 60-mL separatory
funnel containing 2 mL 1MNaHSO
3
.
d. Add 5 mL CCl
4
and1mL1MNaNO
2
to original separatory
funnel containing the aqueous layer and shake for 2 min. Com-
bine organic fractions. Repeat and discard aqueous layer.
e. Shake separatory funnel thoroughly until CCl
4
layer is
decolorized; let phases separate and transfer aqueous layer to a
centrifuge tube. Add 2 mL 1MNaHSO
3
to the separatory funnel
containing CCl
4
and shake for several minutes. When phases
separate, add aqueous layer to centrifuge tube. Add 1 mL dis-
tilled water to separatory funnel and shake for several minutes.
When the phases separate, add aqueous layer to centrifuge tube.
Discard organic layer.
f. To combined aqueous fractions, add 2 mL 6NHCl and heat
in water bath at 80°C for 10 min. Add 1.0 mL PdCl
2
solution
dropwise, with stirring, and digest for 15 min.
g. Cool, stir precipitate, and transfer to a tared filter mounted
in a two-piece funnel. Let precipitate settle by gravity for uni-
form deposition, then apply suction. Wash residue with 10 mL
1NHCl, 10 mL distilled water, and then with 10 mL 95%
ethanol. Dry in a vacuum oven at 60°C for 1 h. Cool in desic-
cator, weigh, mount, and make beta count.
5.
Calculation
Calculate the concentration of radioiodine as given in 7500-
I.B.5.
6. Bibliography
AMERICAN SOCIETY FOR TESTING AND MATERIALS. 1972 Book of ASTM
Standards. Part 23. D 2334-68, American Soc. Testing & Materials,
Philadelphia, Pa.
Figure 7500-I:1. Distillation apparatus for iodine analysis (not to scale).
RADIOACTIVE IODINE (7500-I)/Distillation Method
4
RADIOACTIVE IODINE (7500-I)/Distillation Method
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