Determination of Lead-210 1n Drinking Water
Method 909.0
Richard J, Velten
and
Betty J. Jacobs
Environmental Monitoring and Support Laboratory
U. S. Environmental Protection Agency
Cincinnati, Ohio 45Z68
!
March 1982
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Determination of Lead-210 in Drinking Water
Method 909.0
1. Scope and Application
1.1. Lead-210 is not regulated by the National Interim Primary Drinking
Water Regulations (NIPDWR). However, based upon its maximum
permissible concentration (MFC) published 1n NBS Handbook 69, the
maximum concentration level (MCL) calculated by applying the
formula in the NIPDWR would be 1 pC1/L or less, depending upon the
choice of critical organ.
1.2 The sensitivity of the method as defined in the NIPDWR is
approximately 0.7 pCi/L for a one liter sample size using liquid
scintillation counting and 0.2 pCi/L using a low background beta
counter.
2. Summary of Method
2.1 Lead carrier is added and concentrated by precipitation as the
chromate. It is further purified from its bismuth-210 daughter by
selected dissolution of lead sulfide from a 1.5N_ hydrochloric acid
solution. Lead is finally converted to the carbonate and the
lead-210 concentration calculated by either counting the lead-210
beta emission by liquid scintillation technique or counting the
ingrown bismuth-210 daughter activity by low background end window
counting.
3. Sample Handling and Preservation
3.1 If the sample cannot be analyzed within 24 hours, it is recommended
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that the sample be preserved using nitric acid to a concentration
of 0.01.N (pH 2).
4. Interferences
4.1 Lead-214 will not Interfere as the time delay from lead separation
and counting (10 half lives) allows for Its total decay.
4.2 Lead-212 can Interfere with the lead-210 determination and cause a
positively biased result. However, a 2 to 3 day storage at the end
of Step 8.14 will allow for sufficient decay.
5. Apparatus
5.1 Liquid scintillation counter or low background beta counter
5.2 Millipore 300 ml ground glass filtering assembly
5.3 Membrane filter (PVC), e.g., Gelman 64515
5.4 Centrifuge
5.5 40 ml cone bottom centrifuge tubes
5.6 2.8 cm fiber glass filters
5.7 Convection oven.
6. Reagents
6.1 Acetic add, glacial
6.2 Ammonium carbonate, 1.5*1. Dissolve 144 g ammonium carbonate in
300 ml of water and dilute to 500 ml.
6.3 Ammonium hydroxide, 6M. Transfer 400 ml of concentrated ammonium
hydroxide (SOX) to 500 ml water and dilute to 1000 ml with water.
6.4 Barium carrier, 5 mg Ba^/mL. Dissolve 4.4713 g of
?
2H20 1n water and dilute to 500 ml.
6.5 Bismuth carrier, 5 mg Bi /ml. Dissolve 5.8026 g of
B^NOJ, * 5H20 in 1 M HN03 and dilute to 500 ml with
1 M HMO.,.
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6.6 Hexanolc add, practical.
6.7 Hydrochloric acid, 12 M.
6 M - Transfer 500 ml of concentrated add to 400 ml of water and
dilute to 1000 ml with water.
1.5 M - Transfer 125 ml of concentrated acid to 700 ml of water and
dilute to 1000 ml with water.
6.8 Hydrogen sulfide gas, lecture bottle.
6.9 Lead carrier, 10 mg Pb /ml. Dissolve 4 grains Pb(N03)2 in
250 ml of 0.1 M HNO^
J5.10 Scintillation solution. Commercially prepared universal liquid
scintillation cocktail for aqueous and non-aqueous samples.
6.11 Sodium chromate, 1.5M. Dissolve 175 g of sodium chromate
tetrahydrate 1n 350 ml water and dilute to 500 ml with water.
6.12 Sodium nitrite, 1 M. Dissolve 6.9 g of sodium nitrite in 70 ml
water and dilute to 100 mL with water.
6.13 Toluene, reagent grade.
6.14 Water/ethanol wash solution, 1:1. Mix 200 ml of ethanol with 200
ml of water.
7. Calibration and standardization
7.1 Lead carrier solution
7.1.1 Transfer 10 mL of the lead carrier solution to a 150 mL
beaker and dilute to 75 ml.
7.1.2 Add 1-2 drops of methyl orange indicator and neutralize by
the dropwise addition of 6M NH4OH.
7.1.3 Reacidify with 2 mL of glacial acetic acid and heat to near
boiling.
7.1.4 Slowly bubble H?S gas into the solution for 3-4 minutes.
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7.1.5 Remove hLS source and heat the solution to just boiling.
Cool.
7.1.6 Filter through a tared fritted glass filtering funnel of
fine porosity.
7.1.7 Wash several times with 10 ml portion of water.
7.1.8 Dry at 105-110°C. Cool and weigh.
7.2 Counter Efficiency
7.2.1 Transfer 1 ml each of the lead and bismuth carrier to a 40
ml cone bottom centrifuge tube.
7.2.2 Add an aliquot of the lead-210 standard tracer solution
approximating 1000 dpm.
7.2.3 Dilute to 20 ml and add 1-2 drops of methyl orange.
7.2.4 Neutralize by the dropwise addition of 6M NH4OH.
7.2.5 Reacidify with 2 ml of glacial acetic acid.
7.2.6 Heat to near boiling in a hot water bath and slowly bubble
HgS gas Into the solution for 2-3 minutes.
7.2.7 Remove H^S source and continue boiling for 2-3 minutes.
Remove from bath and cool.
7.2.8 Centrifuge and discard supernate.
7.2.9 Add 20 ml 1.5M HC1 and heat to boiling in a water bath with
Intermittent stirring, breaking up all large sulfide lumps.
7.2.10 Cool and filter through a 2.8 cm glass fiber filter, saving
the filtrate and noting the time of filtration.
;i
7.2.11 Neutralize filtrate by adding 5-6 ml of 6 M NH4OH using pH
paper to verify.
7.2.12 Reacidify by adding 2 ml of glacial acetic acid.
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7.2.13 Heat to near boiling 1n a water bath and slowly bubble H-S
gas into the solution for 2-3 minutes.
7.2.14 Remove H«S source and continue heating for 2-3 minutes.
Cool.
7.2.15 Centrifuge and discard the supernate.
7.2.16 Add 3 ml 6M HC1 and heat in a water bath to dissolve the
sulfides.
7.2.17 Add 0.5 ml of 1M NaN02 to oxidize excess sulfide ions.
Heat until effervescence ceases and dilute to 20 mL with
water.
7.2.18 Filter through a 2.8 cm glass fiber filter, saving the
filtrate.
7.2.19 Dropwise add 6M NH^OH until a pearlescent precipitate
persists. Then add 5 ml 1.5M ammonium carbonate solution.
7.2.20 Heat in a hot water bath with stirring until the excess
o
ammonium carbonate begins to decompose ( 60 C).
7.2.21 Cool and centrifuge, discarding the supernate.
7.2.22 Add 20 ml 1:1 water/ethanol wash solution breaking up the
precipitate with a glass rod.
7.2.23 Filter through a tared 2.8 cm glass fiber filter, washing
the tube and precipitate several times with 10 mL volume of
the wash solution.
7.2.24 Dry filter at 105-110°C. Cool and weigh.
7.3 Liquid Scintillation Counting
7.3.1 Place the weighed filter at the bottom of a glass
scintillation vial with the precipitate facing upwards.
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7.3.2 Add 0.5 ml each of glacial acetic add and water. Evaporate
to dryness 1n an oven at 120°C.
7.3.3 Cool and add 0.25 ml hexanolc acid wetting the filter
completely. Add 3 ml of toluene and swirl occasionally over
a period of 30 minutes to solubllize the lead hexanoate.
7.3.4 Add 10 ml of the scintillation solution, mix thoroughly and
place 1n a liquid scintillation counter.
7.3.5 After 30 minutes, determine the beta spectrum of the
lead-210 emissions.
7.3.6 Set the beta window to include about 95% of the beta
emissions.
7.3.7 Count the standard over a period of two weeks at this window
setting, noting the time of each count.
7.4 Low Background Beta Counter
7.4.1 Transfer the filter from step 7.2.24 to a planchet
conforming to your standard counting geometry. (It would be
desirable to covel? the filter to prevent loss of
precipitate).
7.4.2 Count the standard over a period of two weeks noting the
time of each count.
8. Procedure
8.1 Acidify a 1-liter volume of a tap water sample with 25 mis of
glacial acetic acid.
8.2 Add 10 mgs of lead carrier and 5 mgs of the holdback carriers Bi
and Ba. (Five mgs of these additional holdback carriers, Fe, Co,
Ni, Ce, Mn, Sr, Zn, and Cu may be added when needed.)
8.3 With constant stirring, add 20 mis of 0.5M sodium chromate.
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8.4 Heat to 70° C on a hot plate with stirring until the precipitate
1s fully developed.
8.5 Remove from hot plate and cool 1n a cold water bath.
8.6 Filter with vacuum through a 47 mm 0.45 micron membrane filter.
8.7 Wash precipitate thoroughly with small quantities of distilled
water.
8.8 Transfer the filter to a 40 ml cone bottom centrifuge tube and
dropwise add 1 ml of cone. HC1 contacting the precipitate and heat
in a boiling water bath to reduce the chromate and dissolve the
precipitate. Dilute to 20 mL with water.
8.9 Remove filter and wash with 10 ml water, adding the wash to the
centrifuge tube.
8.10 Add sufficient 6M ammonium hydroxide to neutralize the add.
8.11 Add 2 ml glacial acetic acid and place centrifuge tube 1n a boiling
water bath for 2-3 minutes.
8.12 Carefully bubble a slight stream of hydrogen sulfide gas into the
solution for 2-3 minutes to completely precipitate the lead.
8.13 Remove the hydrogen sulfide source and continue boiling for 5
minutes.
8.14 Remove from the water bath, cool, and centrifuge, discarding the
supernate.
8.15 Add 20 ml 1.5N HC1 to selectively dissolve PbS, heating 1n a
bo,iling water bath. (Precipitate 1s nearly completely solublUzed).
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8.16 Filter through a 2.8 cm glass fiber filter to remove the BigSj
precipitate, collecting the filtrate 1n a clean 40 ml centrifuge
tube. (Note time as Initial Pb-210 separation.)
8.17 Neutralize by the addition of 5-6 ml 6M NH4OH. Add 2 mL glacial
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acetic add and reprecipitate the PbS using H~S gas, heating in a
boiling water bath.
8.18 Cool, centrifuge and discard supernate.
8.19 Add 3 ml 6M HC1 to dissolve the sulfldes and heat in a boiling
water bath. Add 0.5 ml 1M sodium nitrite and heat 1n a hot water
bath until effervescence ceases. Remove from water bath and dilute
to 20 ml with water.
8.20 Filter through a fiber glass filter to remove any precipitated
sulfur or other Insolubles Into a clean 40 ml cone bottom
centrifuge tube. Wash with 10 ml water.
8.21 Add sufficient-6^1 ammonium hydroxide to neutralize the acid.
8,22 Add 5 ml of 1.5M ammonium carbonate.
8.23 Heat in a boiling water bath for 3 minutes, remove and cool.
8.24 Centrifuge and discard the supernate.
8.25 Wash precipitate with 15 ml of 1:1 water-.ethanol solution.
8.26 Filter through a tared 2.8 cm fltfer glass filter and rinse with 10
ml 1:1 water/ethanol solution. "
8.27 Dry at 105°C, cool and weigh to determine lead carrier recovery.
(If liquid scintillation counting 1s to be used, continue at step
8.28. If Low Background Beta counting is to be used, continue at
step 8.33).
8.28 Place filter at the bottom of scintillation vial with the
precipitate facing upwards.
8.29 Add 0.5 ml glacial acetic acid and 0.5 ml water and take to dryness
in a 120°C oven.
8.30 Cool and add 0.25 ml of hexanoic add and 3 ml toluene. Mix and
let stand for 20 minutes with occasional mixing.
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8.31 Add 10 ml of scintillation solution. Mix throughly and place
sample Into the liquid scintillation counter.
8.32 Using the predetermined window setting for counting only the
lead-210 beta emissions, count for sufficient time to meet the
method detection limit.
8.33 Place the filter on a planchet conforming to your standard
geometry. (It would be desirable to cover the filter to prevent
loss of precipitate during storage.)
8.34 Store for about 2 weeks to allow sufficient B1-210 Ingrowth.
8.35 Place 1n the counter and count for sufficient time to meet the
method detection limit and note time of count.
Calculation
9.1 Lead standardization
Lead, mg/mL = mg PbS x 0.86599
TO
9.2 Liquid scintillation counter
9.2.1 Bismuth-210 crosstalk (Z)
9.2.1.1 Determine the bismuth ingrowth factors, (1-e )
where t equals the time difference from time of
separation (step 7.2.10) to time of counting for the
various count times.
9.2.1.2 Plot the observed count rates as the ordinate
against the ingrowth factors.
9.2.1.3 By linear least squares analysis, solve for the
Intercept, A, and slope, B. (The Intercept 1s the
count rate due to the lead-210 emission and the
slope 1s the count rate due to the amount of the
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for the various count times where t is the time
difference between time of separation and time of
count.
9.3.1.2 Plot the observed count rates as the ordlnate
against the ingrowth factors.
9.3.1.3 By linear least square analysis solve for the
intercept A and slope B. (The intercept A
represents the count rate due to lead-210 and the
slope B represents the count rate of bismuth-210 at
equilibrium.)
9.3.1.4 Efficiency determination
Lead-210 efficiency, E ^ = A/dpm recovered
Bismuth-210 efficiency, E ~ s B/dpm recovered
Total efficiency = E 1 + E 2 (1 -e~U)
9.3.2 Concentration
Lead-210 concentration pCi/L = G - B
Vx (E1+E2(1-e'U)) x R x 2.22
where:
G = gross count rate in lead-210 window
B = background count rate
V = volume of sample, liter
E] = Lead-210 efficiency
£2 = Bismuth-210 efficiency
(1-e *) = Bismuth-210 ingrowth factor
R = chemical recovery
2.22 - constant (dpm/pCi)
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10. Precision and Accuracy
10.1 Liquid scintillation counting
10.1.1 Accuracy
10.1-1.1 Four samples at lead-210 concentrations ranging from
0 to 41 pCi/L were analyzed. A plot and linear
least square solution of pCi/L found versus pCi/L
added showed that the intercept was not different
from zero and that the slope showed a +1X bias.
10.1.1.2 Seven samples were also analyzed at a single
concentration level (7.72 pCi/L). The average of
the seven determinations was 7.96 pCi/L. This
showed a +3% bias.
10.1.2 Precision
10.1.2*7 Based upon the seven replicate values at 7.72 pCi/L,
the relative standard deviation was found to be ± 8X.
10.2 Low background beta counting
10.2.1 Accuracy
10.2.1.1 Eight samples were analyzed at a single
concentration level of 7.72 pCi/1. The average
concentration found was 7.85 pCi/1. This shows as
+2% bias.
10.2. Precision
10.2.2.1 Based upon the eight replicate values at 7.72 pCi/1,
the relative standard deviation was calculated to be
+ 5X.
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