AN-1414

Rapid Determination of 90Sr in up
to 40 Liter Seawater Samples

Summary of Method Yttrium-90, the daughter product of 90Sr decay, is separated and concentrated from up to40L samples of seawater. A ferric hydroxide precipitate enhanced with 10mg of lanthanum and 1mg of yttrium
concentrates 90Y, while rejecting much of the salt content of the seawater sample. A second precipitation withlanthanum fluoride removes additional matrix ions. Yttrium is separated from potentially interfering radionuclides in thesample, including rare earths such as 138La and 139/144Ce, using a 2mL cartridge of Eichrom DGA Resin. 90Y is measured
on a low background gas flow proportional counter following cerium fluoride microprecipitation onto an EichromResolve® Filter. Chemical yield of stable yttrium is determined by ICP-MS or ICP-AES. Average chemical recovery ofyttrium is 84 + 7% for 40L samples. Measured values of 90Sr(90Y) agree to within 5% of reference values, with two hourcount times. The minimum detectable activity for 90Sr for 40L samples with a two hour count time is 0.35mBq/L. Theaverage time to complete the method is 8 hours. While standard methods targeting Sr are limited by the ~8mg/L native
Sr content in seawater, targeting 90Y directly allows for the efficient processing of very large seawater samples toachieve very low minimum detectible activities. However, interference by theFigure 1. Sample Preparation
fission product 91Y (t1/2 = 58.51 days) precludes application of this method
for the measurement of 90Sr(90Y) immediately following a radiological incident
Up to 40L Sample of Seawater.
involving the release of un-aged nuclear fuel or fission products.
Acidify to pH 2 with 37% HCl.
Reagents
DGA Resin, Normal 2mL Cartridges (Eichrom DN-R50-S)
Nitric Acid (70%)
Hydrochloric Acid (37%)
Hydrofluoric Acid (49%) or Sodium Fluoride
Ammonium Hydroxide (listed as 28% NH3 or 56% NH4OH)
Deionized Water
Iron Carrier (50mg/mL Fe, as ferric nitrate)
Yttrium and Cerium Carriers (1mg/mL)
Lanthanum Carrier (10mg/mL)
1.25M Ca(NO3)2
2M Al(NO3)3
90Sr standard
Boric acid
Equipment
Vacuum Box (Eichrom AR-24-BOX or AR-12-BOX)
Cartridge Reservoir, 20mL (Eichrom AR-200-RV20)
Inner Support Tubes-PE (Eichrom AR-1000-TUBE-PE)
Yellow Outer Tips (Eichrom AR-1000-OT)
Resolve Filters in Funnel (Eichrom RF-DF25-25PP01)
50mL and 500mL Centrifuge TubesCentrifuge
Gas Flow Proportional Counter
Analytical Balance
Vacuum Pump
Heat Lamp

Add 1mg Yttrium carrier.
Add 10mg La carrier. Add 50mg Fe carrier
per liter of sample. Mix Well.
Adjust to pH 9 with 56% NH4OH. Mix.
Allow precipitate to settle.
Decant supernate until ~2L remains.
Transfer remaining supernate and precipitate
to 500mL centrifuge tubes. Centrifuge
3000rpm for 10 minutes. Decant supernate.
Repeat until entire sample centrifuged.
Wash precipitate with 100mL water.
Centrifuge. Decant supernate.
Dissolve precipitate in 100mL 1.5M HCl.
Add 75mg Ca and 50mL 49% HF. Mix.
Wait 15 minutes. Centrifuge. Decant supernate.
Dissolve precipitate in 10mL 3M HNO30.25M Boric acid, 10mL 70% HNO3,
and 10mL 2M Al(NO3)3.
Load Solution for Sr separation.

Figure 2. Yttrium Separation on DGA and CeF3 Microcprecipitation(1) Precondition DGA Resin with5mL 8M HNO3.
(2) Load sample at
1-2mL/min.
(3) Rinse sample tube with 5mL
8M HNO3.
(4) Add tube rinse to DGA Resin.
Elute at 1-2mL/min.
(5) Rinse DGA Resin sequentiallywith:- 15 mL 8M HNO3 (Ca,Sr,Pb)- 20mL 0.05M HNO3 (La,Ce,Sr,U)- 15mL 3M HNO3-0.25M HF (U,Th)- 10mL 3M HCl (Ca,La,Pb)(6) Dispose of (1) to (5) as waste.
(7) Strip Y with 20mL
0.25M HCl at
1mL/min.

(8) Remove 0.1-1.0mL aliquot for
stable Y recovery by ICP-MS orICP-AES. Dilute aliquot asappropriate.
(9) To remaining sample:- Add 100ug Ce carrier.
- Mix well.
- Add 2mL 49% HF.
- Mix well. Wait 15-20 minutes.

(16) Draw vacuum until filter is dry.
(17) Remove filter from funnel
assembly and mount filter on
stainless steel planchet withadhesive tape.

(10) Set up Resolve® Filter Funnel
on vacuum box.
(11) Wet filter with 3mL 80% ethanol
followed by 3mL DI water.
(12) Filter sample.
(13) Rinse sample
tube with 5mL
DI water andadd to filter.

(18) Dry filter under heat lamp for
10-15 minutes.
(19) Measure 90Y on low background gas flow proportionalcounter.

(14) Rinse filter funnel
with 3mL DI water.

2mL DGA
Cartridge
90Y(15) Rinse filter funnel
with 1-2mL 100%ethanol.

Method Performance 10-40L Spike Seawater Samples
9090Sample% Recovery
Sr (mBq/L)
Sr (mBq/L)
Volume, L
Y carrier
Reference
Measured1085.5
296
310
20
89.2
28.2
28.1
30
72.3
18.8
18.5
40
87.6
14.1
13.7
40
86.5
14.1
13.9
MDA for 40L sample = 0.35 mBq/L for 2 hour count timeMDA for 40L sample = 0.20 mBq/L for 8 hour count time% Bias
4.7-0.4-1.6-2.8-1.4

References
1) Sherrod L. Maxwell, Brian K. Culligan, Jay B. Hutchinson, Robin C. Utsey, Daniel R. McAlister, “Rapid determinationof 90Sr in seawater samples,” J. Radioanal. Nucl. Chem., 303, 709-717 (2015).
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