AN-1404

Rapid Determination of Sr in
1-2 Liter Seawater Samples

Summary of Method Strontium is separated and concentrated from 1-2L samples of seawater with a calcium
phosphate precipitation, enhanced with 200mg of iron. Strontium is separated from matrix impurities and potentiallyinterfering radionuclides in the sample using two stacked 2mL cartridges of Eichrom Sr Resin. Radiostrontium ismeasured on a low background gas flow proportional counter or liquid scintillation counter. Chemical yield of strontium
is determined by gravimetric recovery of native stable strontium in the seawater or by ICP-AES measurement. Averagechemical recovery of strontium is 89 + 5% for 1L samples and 82 + 4% for 2L samples. Measured values of 90Sr agreed
to within 1% and 4% of reference values, for 1L and 2L, respectively, with two hour count times. The minimum
detectable activity for 90Sr for 2L samples with a two hour count time is 9.1Bq/L. A single operator can prepare batchesof 12-24 samples for measurement of radiostrontium in less than 8 hours.
Reagents
Sr Resin, 2mL Cartridges (Eichrom SR-R50-S)
Nitric Acid (70%)
Ammonium Hydroxide (listed as 28% NH3 or 56% NH4OH)
Deionized Water
Iron Carrier (50mg/mL Fe, as ferric nitrate)
3.2M (NH4)2HPO4
2M Al(NO3)390Sr standard
Oxalic acidFigure 1. Sample Preparation
1-2L Sample of Seawater.
Add 200mg Fe(III), and 25mL
3.2M (NH4)2HPO4.
Mix Well.
Adjust to pH 10 with ~30mL of 56%
NH4OH while stirring.
Centrifuge for 10 minutes in 250 or 500mL
tubes at 3000rpm, decanting supernate towaste, until entire sample has been processed.

Wash precipitate with 50mL of pH 9 NH4OH.
Equipment
Vacuum Box (Eichrom AR-24-BOX or AR-12-BOX)
Centrifuge for 10 minutes at 3000rpm.
Cartridge Reservoir, 20mL (Eichrom AR-200-RV20)
Decant supernate to waste.
Inner Support Tubes-PE (Eichrom AR-1000-TUBE-PE)
Yellow Outer Tips (Eichrom AR-1000-OT)
Dissolve precipitate in 25mL 70% HNO3.
50mL Centrifuge Tubes
Transfer to 50mL centrifuge tube.
250-500mL Centrifuge Tubes
Centrifuge
Rinse centrifuge tube with 8mL 2M Al(NO3)3 and 5mL 3M HNO3.
Cupped Stainless Steel Planchets (~5mL volume)
Transfer tube rinse to Sr samples in 50mL centrifuge tube.
Gas Flow Proportional Counter
Hot Plate
Analytical Balance
Load Solution to Sr Resin Separation.
Vacuum Pump

Figure 2. Strontium Resin Separation (Optional 90Y Ingrowth)(1) Precondition Sr Resin with
10mL 8M HNO3.
(2) Load sample at 1-2mL/min.

Gas Flow Proportional Counting*:(3) Rinse sample tube with 5mL
8M HNO3.
(4) Add tube rinse to Sr Resin.
Elute at 1-2mL/min.
(5) Rinse Sr Resin sequentially with:- 15 mL 8M HNO3- 10mL 3M HNO3 - 0.05 oxalic acid- 10mL 8M HNO3

(8) Evaporate samples to dryness
on tared cupped stainless steelplanchets.
(9) Rinse Sr sample vials with 2mL
0.05M HNO3. Transfer vial rinse toplanchets. Evaporate to dryness.

(6) Dispose of (1) to (5) as waste.
(7) Strip Sr with 20mL
0.05M HNO3 at
1mL/min.

*(Options for 89/90Sr Discrimination)(a) Sr fraction from step (7) can betransferred to a liquid scintillation vial.
89Sr can be measured by Cerenkov
counting (no LSC cocktail). 89/90Srcan then be measured by addingliquid scintillation cocktail.
(b) Sr fraction from step (10) can be
dissolved in 10mL 8M HNO3 after >7days of 90Y ingrowth. 89/90Sr can beremoved on Sr Resin. 90Y will elute in
Sr Resin load and can be counted byliquid scintillation or gas flow
proportional counting.

(10) Weigh planchets on an
analytical balance to determine
gravimetric yield of stable Sr(NO3)2.

2 x 2mL
Sr Resin
Cartridges(11) Measure radiostrontium insamples on low background gas
flow proportional counter.
90Sr90

Performance of Sr Method for 1L and 2L Seawater Samples
SampleSampleReplicates Volume, L
111
490Sr, Reference
Value (mBq/L)
148

2

148

90Sr, Measured
Value (mBq/L)
150 + 11% Bias
1.2Sr carrier% Recovery
89 + 5154 + 54.2

82 + 42 hour count times
MDA = 9.1 mBq/L for 2L sample

References
1) Sherrod L. Maxwell, Brian K. Culligan, Robin C. Utsey, “Rapid determination of radiostrontium in seawater samples,”J. Radioanal. Nucl. Chem., 298(2), 867-875 (2013).
1955 University Lane Lisle, IL 60532, USA+1 (630)963-0320

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