Determination of Po1on1um-2lO
In Drinking Water by Alpha Particle Counting
Method 912.0
Richard J. VeHen
and
Betty J. Jacobs
Inorganic Analyses Section
Physical and Chemical Methods Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio
October 1983
-------
Determination of Po1on1um-2lO 1n
Drinking Water by Alpha Particle Counting
Method 912.0
1. Scope and Application
l.l This method is applicable to the determination of polon1um-210
(Po-210) In drinking water samples.
1.2 The method detection limit as defined by the National Interim
Primary Drinking Water Regulations 1s 0.1 pC1/L based on an
Instrumental alpha particle background of 0.1 count /minute and a
100-minute counting period.
1.3 This method may be applied to surface and ground water samples
provided these samples are Immediately filtered upon collection.
2. Summary of Method
771Lead is added as a nonisotopic carrier and the polonium-210 is
concentrated by coprecipitatlon on lead sulfide from an acetic acid
solution using hydrogen sulfide gas. The lead sulfide is collected
by filtration and dissolved in concentrated nitric acid. Nitrates
are removed by fuming with a small quantity of perchloric acid.
The solution is treated with diluted hydrochloric acid and the
polonium-210 1s spontaneously electroplated onto a nickel disk.
The nickel disk 1s washed, dried, and alpha.counted.
3. Safet
371Hydrogen sulfide gas is not only toxic but also highly flammable.
Its use should be restricted to well ventilated hood facilities and
--away-from all open flames.
3.2 Perchloric acid is used in a very limited amount.. Adequate
precautions should be taken to insure that the acid fumes are
purged through a water trap when not used 1n hoods specifically
designed for perchloric acid usage. ~
4. Apparatus
471Concentric ring water bath.
4.2 Plating cell, 8 ounce plastic nursing bottle (See Fig. 13.1).
4.3. Stirring motor with glass stirrer.
4.4 Internal proportional counter, -
4.5 Membrane filtering assembly, 300 ml.
5. Reagents
5.1 Acetic acid, glacial, CAS Reg 64-19^7, 99.7% w/w.
5.2 Acetone, CAS Reg 67-64-1.
5.3 Anmonium hydroxide, CAS Reg 1336-21-6 (NfyOH) 6N. Dilute 400 ml
of concentrated ammonium hydroxide to 1000 ml uling distilled water.
5.4 Hydrochloric acid, CAS Reg 7647-01-0. (HC1) 0.5N. Dilute 42 ml
36-381 HC1 to 1000 mL using distilled water.
5.5 Hydrogen sulfide'gas (H?S). Lecture bottle 99.5%.
5.6 Lead nitrate carrier solution, CAS Reg 10099-74-8, (Pb(N03>9)
0.1N. Dissolve 16.5g lead nitrate (Pbfffl^);) In 500 mL of 6.IN
nitfic acid. 1 mL • 10.4 mg lead ion. ~
-------
5.7 Methyl red, CAS Reg 493-52-7. O.lt w/v. Dissolve 0.1 g methyl red
1n 100 * water.
5.8 Nickel disk — 1.5-Inch diameter by 0.020-Inch In thickness.
Highly polished on one side.
S.9 Nitric add, CAS Reg 7697-37-2. (HNCh) 69-71* w/w.
5.10 Perchloric add, CAS Reg 7601-90-3, (HC104) 70-72% w/w.
6. Sample Collection, Preservation and Storage
6.1 sample Collection
6.1.1 Sampling should conform to ASTM 03370-76, "Standard
Practices for Sampling Water."
6.2 Preservation and Storage
6.2.1 Sample should be preserved by the addition of nitric add to
a strength of 0.1N (6 ml 69-72% per liter of sample).
6.2.2 Preserved samples'need not be refrigerated for storage.
However, analysis should be performed as soon as possible
and before 60 days after collection.
6.2.3 All samples shall be collected and stored In plastic
containers.
7. Calibration and Standardization .
771Internal proportional counter efficiency
7.1.1 Transfer an aliquot containing 200-500 d/m of polonium 210
to a 150-mL beaker.
7.1.2 Add 1 ml of the lead nitrate solution, 20 nt concentrated
nitric acid and 1 at of perchloric acid.
7.1.3 Cover with a watch glass and evaporate to dense fumes of
perchloric acid.
7.1.4 .Remove from hot plate, cool, and dissolve residue in 20 ml
of 0.5N hydrochloric acid.
7.1.5 Assemble plating cell and fill with water to check for
leaks. Discard water if no leaks are present.
7.1.6 Transfer solution to'plating cell and rinse the beaker four-
more times with 20 ml of 0.5N HC1.
7.1.7 Place plaxing cell In boiling water.bath, immerse the glass
stirrer. stir and plate for 4 hours.
7.1.8 Remove stirrer, discard solution, and rinse disk with water.
7.1.9 Disassemble cell, remove disk, rinse with water and acetone,
dry and count for a period of time* to accumulate at least
10,000 counts. -.""••
7.1.10 Calculate counter efficiency, c/m/d/m.
7.2. Recovery Factor
7.2.1 Spike triplicate l-l aliquots of tap water with a known
quantity of Po-210 tracer (1000 d/n).
7.2.2 Analyze these aliquots as prescribed in Section 9.0,
Procedure.
7.2.3 Determine recovery factor (RF) as shown in Section 10.0,
Calculation.
8. Quality Control
871General Requirements
8.1.1 All analysts using this method are required to demonstrate
their ability to use the method and to define their
respective accuracy and precision criteria.
-------
8.1.2 The minimum requirements for the establishment of accuracy
and precision criteria Is four replicate analyses of an
externally prepared performance evaluation sample..
8.1.3 Application of this method to samples of different matrix
composition requires the analyst to demonstrate Us
successful use by the addition of a standardized spue
solution and evaluation of the spike recovery.
8.2 Requirements In support of National Interim Primary Drinking Water
Regulations (NIPOWR) regulations.
8.2.1 The laboratory must be certified.
8.2.2 The laboratory must participate once each year in an unknown
performance study for polonlum-210 administered by EPA.
8.2.3 The laboratory must participate at least twice each year 1n
EPA laboratory Intercomparison studies for polonlum-210.
8.2.4 To verify Internal laboratory precision for polonium-210, a
minimum of 10 percent duplicate analyses must be performed.
8.2.5 When 20 or more polonium-210 analyses are performed in a
day, a performance standard and a background sample must be
measured with each 20 samples. If less than 20 samples are
performed 1n a day. a performance sample and a background
sample, must be measured along with the samples.
8.2.6. Quality control performance charts, or performance records,
must be maintained.
8.3 Requirements for Non-Regulated Activities
8.3.1 It is recommended that the requirements criteria specified
for the NIPOWR be adopted for all study activities.
•r
8.4 Acceptance Criteria
8.4.1 Support of NIPOWR . »,,...
8,4.1.1 Analytical results must conform to control limits
established by EPA as "described In "Environmental
Radioactivity Laboratory Intercomparlson Studies
Program - FY 1977," (EPA-600/4-77r001) or in
subsequent revisions.
8.4.1.2 Duplicate measurements are considered acceptable
when the difference between them is less than two
standard deviations as described in EPA 600/4-77-001
or subsequent revisions. . . .,, w
8.4.1.3 The performance standard measurement will be
considered acceptable when the difference between
the observed or measured value and the true value is
less than two standard deviations as described in
EPA-600/4-77-001 or subsequent revisions.
8.4.2 Support of Non-Regulated Activities
8.4.2.1 It is reconmended that the following hierarchy be
used for the setting of accuracy and precision
statements. . „-...,
8.4.2.1.1 Defined by Purpose of Study
8.4.2.1.2 Defined by Interlaboratory Collaborative
Study
8.4.2.1.3 Defined by Intralaboratory -
Multi-operator Study
-------
8.4.2.1.4 Defined by Single Operitor Study
8.4.2.2 Duplicate measurements are considered acceptable
when the difference between then Is less than two
standard deviations as described In Section
8.4.2.1.1 through 8.4.2.1.3. Duplicate measurements
are considered acceptable when the difference
between them Is less than three standard deviations
as described 1n Section 8.4.2.1.4.
8.4.2.3 The performance standard measurement 1s considered
acceptable when the difference between the observed
and true value 1s less than two standard deviations
as described In Sections 8.4.2.1.1 through
8.4.2.1.3. The performance standard measurement Is
considered aceptable when the difference between the
observed and true value 1s less than three standard
deviations as described 1n Section 8.4.2.1.4.
9. Procedure
971Neutralize a 1-L aliquot of the acid preserved sample to the basic
side of methyl red using 6N NH^OH.
9.2 Add 25 nt glacial acetic ac~1d and .1 mL of the lead nitrate carrier
solution. Mix thoroughly.
9.3 Heat to near boiling on a hot plate and precipitate the lead by
bubbling a slow stream of hydrogen sulflde gas Into the solution
for 3 minutes. '- " ••""-.
9.4 Remove the hydrogen sulfide source, and continue boiling for 1
minute. Remove from hot plate and allow to cool until cool enough
to safely handle.
9.5 Filter the solution through a 47 mm 0.45 micron cellulose
triacetate membrane filter; Discard the filtrate.
9.6 Transfer the filter to a 100-mL beaker and add 20 ml concentrated
nitric add and 1 ml perchloric add.
9.7 Evaporate to the first signs of dense fumes of perchloric acid.
Remove from hot plate.
9.8 Assemble the plating cell and fill with water to check for leaks.
Discard water 1f cell is watertight, or reassemble and test 1f
found to leak. -:
9.9 Add 20 ml 0.5N HC1 to the perchloric acid residue and dissolve.
Heat, If neceTsary. • -
9.10 transfer solution to plating cell.. .
9.11 Rinse beaker'four more times using 20 mL 0.5N HCT each time and
adding each rinse to the plating cell. ""
9.12 Immerse plating cell 1n a boiling water bath, position the electric
stirring motor, and stir without cavitation for 4 hours.
9.13 Remove stlrrer from cell and remove the plating cell from the water
bath.
9.14 Discard plating solution and rinse cell two tines using water
rinses.
9.15 Disassemble the cell, and rinse both sides of the nickel disk with
water and acetone.* - . .
9.16 Place in a 60°C drying oven for several minutes to dry. Remove
from oven and cool in desiccator.
9.17 Count for 100 minutes in an internal proportional counter.
-------
10. Calculation
10.1 Counter Efficiency (E) (Sec. 7.1)
10.1.1 Compute counter efficiency by calculating the ratio of the
observed counts per minute to the added disintegration per
minute (c/m/d/m)
f Observed count rate (c/m)
" Disintegration rate (d/m)
10.2 Recovery Factor (RF) (Section 7.2)
10.2.1 Determine recovery factor by calculating the ratio of the
observed counts per /minute recovered to the added
disintegration rate.
RF Observed (c/m) recovered
" Added disintegration rate (d/m) x E
10.3 Polonium Concentration
10.3.1 Determine the concentration of the polonium-210 activity by
dividing the observed counts per minute by the counter
efficiency, recovery factor, sample volume, and the
conversion factor 2.22 d/'m/pCI
Po 210 oCi/L Sample observed count rate
v ' ~ E x RF x V X 2.22
where:
E « Counter Efficiency
RF m Recovery Factor
V * Volume in liters
2.22 = Conversion factor (d/m)/(pCi)
11. Precision and Accuracy
11.1 Single operator precision
11.1.1 The precision of the method has been evaluated by the
analysis of seven replicate samples at the 10.02 pCi/L
concentration level. The precision also includes the
counting error which has been determined to be 31 at the
1 S.D. confidence level. The calculated precision has been
. found to be * 5.3%.
11.2 Single. Operator Accuracy . . .
11.2.1 The average concentration found for the seven replicate
analyses was 10.44 pCi/L and ranged from a low of 9.83 to a
high of 11.11 pCi/L.
11.2.2 Bias Is calculated to be a positive 4.11.
12. References .
Blanchard, R. I., et al., Environmental Science and Technology, 1967, 1,
Figgins, P.E., National Academy of Science, National Research Council.
1961. NAS-NS 3037. • .
13. Appendix
13.1 Plating Cell Assembly (Figure 13.1)
13.1.1 Drill a hole in the bottom of an 8 oz. plastic nursing
bottle to accept the glass stirrer.
-------
13.1.2 Using a band saw, cut off a 3/4 to 1-1nch section of the
bottom to use as a cell cover to prevent excessive
evaporation during the plating period.
13.1.3 Using emery cloth, remove the molded seams across the top of
the mouth to make a flat seal with the nickel disk.
13.1.4 Cut out the rubber nipple and use the flange as the gasket.
13.1.5 Over-tightening of the closure tends to cause leakage.
13.1.6 Keeping the water level of the boiling water bath at a
higher level than the plating solution prevents any minute
leakage out of the cell during plating.
13.1.7 Weight may have to be added to the cover to keep the cell
submerged.
13.1.8 It Is advantageous to fabricate a plastic or metal
concentric ring for the water bath with just a large enough
hole to accept and stabilize the plating cell.
-------
\
3---.=*
STIRRING
MOTOR
CUT OFF BOTTOM
USED AS
COVER
GLASS
STIRRER
INVERTED PLASTIC
NURSING BOTTLE "
NICKEL DISK
RUBBER GASKET
SCREW-TOP CLOSURE
PLATING CELL ASSEMBLY
FIGURE 13.1
------- |