DETERMINATION OF PLUTONIUM IN DRINKING HATER
METHOD 911
by
Richard J. Velten
Betty J. Jacobs
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
•U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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Determination of Plutonium In Drinking Water
Method 911
1. Scope and Application
1.1 This method covers the measurement of total plutonlum alpha
particle activity 1n water samples.
2. Summary of Method
2.1 An acidified aliquot of the sample 1s treated with bismuth carrier
and the plutonlum 1s oxidized to the tetravalent state using sodium
nitrite. Bismuth phosphate carrying the plutonlum 1s precipitated
from a heated solution and filtered. After treatment with 8N HC1,
the plutonlum 1s extracted Into tr1-1so-octylam1ne (TIOA). The
plutonlum 1s reduced with hydrlodlc add, and separated from the
TIOA. The add solution 1s taken to dryness and the plutonlum 1s
dissolved in dilute HC1. Lanthanum fluoride carrying the plutonlum
Is precipitated and counted.
3. Sample Handling and Preservation
3.1 Tetravalent plutonium in weakly acidic or neutral solutions may
hydrolyze to form colloids. Samples should be acidified as soon as
possible after collection to maintain the plutonium 1n an Ionic
form.
3.2 Since polymeric plutonlum is slowly dissolved in slightly acidic
solutions, it is recommended that samples be stored for several
days prior to analysis.
4. Interferences
4 1 Alpha activity 1s present to various degrees in the lanthanum
carrier. If the activity associated with the lanthanum carrier Is
not determined, it will interfere in the determination. Lanthanum
reagent equivalent to < 0.2 cpm/mg lanthanum ion 1s satisfactory.
5. Apparatus
5.1 Gas-flow internal proportional counting system or alpha scintill-
ation detection system.
5.2 Stirring hot plates.
5.3 Separatory funnels, 125 mL.
5.4 Large Millipore glass filtering apparatus, and 47 mm diameter 0.45y
PVC filters.
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5.5 Stainless steel planchet, 2-1nch diameter.
6. Reagents
6.1 All chemicals should be of reagent grade or equivalent whenever
they are commercially available.
6.2 Alcohol-acetone mixture; mix equal volumes of 95% ethanol and
acetone.
6.3 Bismuth carrier, 10 mg/mL; dissolve 5.8 g Bi(N03)3 • 5H20
1n 250 mL of 0.5N HMOs-
6.4 Ethanol 95%.
6.5 Hydrochloric add, 12N; concentrated
0 y 8H; add 300 ml 12N HCL to 150 ml water.
6.6 Hydrofluoric add, 48%.
6.7 Hydr1od1c add, 47%.
6.8 Lanthanum carrier, 5 mg/mL; dissolve 1.55 g La(N03)3 • 6H20
in 100 mL of 0.1N HN03.
6.9 Nitric acid, concentrated, 16N..
6.10 Phosphoric acid, 11M; dilute 100 mL concentrated phosphoric acid
with 300 mL water.
6.11 Sodium bisulfate, 5%; dissolve 10 g NaHS04 in 100 mL water and
carefully add 100 mL of 3W U2$Q4 while stirring.
6.12 Sodium 'nitrite, solid.
6.13 Tri-1so-octylamine (TIOA) 10% in xylene; dilute 50 mL TIOA to 500
mL using xylene.
Calibration
7 1 Determine the counting efficiency factor (E). by transferring a
' known amount of standardized P^p"1^:"* Jracer. *o* o^thP
containing 50 mL of water and 2 mL of 12N HC . Add 1 mL of the
lanthanumwrrier and mix. With constant stirring, add 2 mL of 48%
HF, and allow to stand .for 30 minutes with occasional st jrlng.
Filter through a 47 mm membrane filter, wash two times with 10 mL
each of wate? and ethanol. Transfer the filter to a 2-Inch stain-
less steel planchet previously coated with rubber cement and
containing 5 drops of 1:1 acetone-alcohol mixture. Dry at 80°C
for 3-5 minutes. Count for sufficient times (50 minute) to
accumulate a total of 104 total counts.
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Counting efficiency, E • -
where: A « Gross counts per minute of standard
B » Reagent blank
C - dpm of standard used
8. Procedure
8.1 To a liter of water, add sufficient nitric add to make the solu-
tion 0.25N 1n nitric add (Note 1).
8.2 Add 5 ml of bismuth carrier and 0.5 grams sodium nitrite.
8.3 Heat to 70°C with slow stirring on a hot plate magnetic stlrrer.
8.4 Add 5 ml of 11M phosphoric add and mix vigorously for 30 seconds.
8.5 Turn off heat and stir slowly for 30 minutes. Remove from stlrrer,
retrieve magnetic stirring bar and allow the precipitate to settle
for 20-30 minutes. (Note 2).
8.6 Filter through a 47 ran membrane filter, transferring the bulk of
the precipitate to the filter near the end of the filtration.
8.7 Wash the remaining precipitate from the beaker using a jet stream
of water. Discard filtrate.
8.8 Transfer the filter to a 50 mL beaker and dissolve precipitate in
20 mL of 8N. HC1.
8.9 Transfer the solution to a 125 ml separatory funnel containing 25
mL of equilibrated 10X TIOA.
8.10 Wash the filter and beaker twice with 15 mL of 8N_ HC1, adding the
washings to the separatory funnel.
8.11 Cap the separatory.funnel and shake vigorously for two minutes.
i f
8.12 Allow the phases to'separate for 5-10 minutes and discard the lower
acid layer. ' -.' :.'
••-; • j i
8.13 Wash the organic layer two'times using 10 mL portions of BH HC1 by
shaking for 30 seconds, discarding the lower acid phase after
adequate separation. '''*"'.'
8.14 Back-extract the plutonium by extracting three times for 1 minute
each using 10 mL portions of 8N HC1 containing 0.1 mL of 47X HI,
combining all separated acid pFases in a 50 mL beaker. Discard the
organic layer.
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8.15 Evaporate the combined extracts to near dryness. Remove from hot
plate and cool.
8.16 Add 2 mL of acid NaHS04 solution and 5 ml of 16N HNOa.
8.17 Evaporate to complete dryness. If organic material 1s not
completely oxidized, place beaker 1n a muffle furnace at 400°C
and ash until organic material 1s removed.
8.18 Remove from furnace and cool. Add 2 mL of 12N HC1 and rotate
beaker slowly to moisten the residue. Dilute to 50 mL with water.
8.19 Add 1 mL of lanthanum carrier and mix.
8.20 With constant stirring, add 2 mL of 48X HF, and allow to stand for
30 minutes, mixing Intermittently.
8 21 Filter through a 47 mm membrane filter and wash two times with 10
mL portions of water and two times with 10 mL portions of ethanol.
8.22 Transfer filter to a 2-Inch stainless steel planchet previously
coated with rubber cement and containing 5 drops of the alcohol-
acetone mixture. (Note 3).
8.23 Place 1n drying oven at 80°C for 3-5 minutes.
8 24 Count for a 100 minute interval in an internal proportional counter
or scintillation counter, or store in a desiccator until ready to
count.
Notes- 1. If sample has been preserved with nitric acid, ascertain
how much acid was used and make the necessary adjustments.
2. While waiting for precipitate to settle, pre-equilibrate
the TIOA by shaking 25 mL each of TIOA and 8N. HC1 for two .
minutes and allowing the phases to separate. Discard
acid.
3. To facilitate the mounting of the filter, it is.
recommended that the filter be rolled onto the planchet,
thereby eliminating entrapped air pockets.
9. Calculation
9.1 Plutonium concentration, pCI/L - S - B
E x 2.ZZ x V
where: S » gross counts per minute
B = reagent blank including instrument background
E » detector efficiency, cpm/dpm
2.22 = constant to convert dpm to pC1, pd/dpm
V « sample volume in liters
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10. Precision and Accuracy
10.1 Eight 1-Hter allquots of tap water were spiked with a standard
Pu-236 solution to a concentration of 8.5 pC1/L. Single laboratory
results of the analyses were 9.1. 7.9, 6.1, 8.4, 7.0, 7.2, 8.1, and
9.4 pCI/L. The precision 1s calculated to be 1.1 pCI/L and the
average concentration 7.9 pC1/L. Relation precision Is estimated
at 14* and average recovery 1s estimated at 93X.
11. References
11.1 George Coleman, "The Radiochemistry of Plutonium," NAS-NS 3058,
1965.
11.2 Fletcher L. Moore, "Liquid-Liquid Extraction with High-Molecular
Weight Amines," NAS-NS 3101. 1960.
11.3 T. 6. Scott, S. A. Reynolds, "Determination of Plutonium 1n
Environmental Samples - Part II Procedures," Radiochem. RadloanaV.
Letters, 23 (4) 275-281, (1975).
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