AN-1402

Rapid Determination of Sr inEmergency Milk Samples

Summary of Method Strontium is separated and concentrated from 100mL milk samples using a calcium
phosphate precipitation. The precipitate is dissolved with nitric acid and centrifuged to remove residual protein and fat.
The supernate, containing Sr, is wet ashed with HNO3-H2O2 and then heated in a muffle furnace at 550°C for 30-60
minutes to destroy any residual organic matter. The muffled residue is wet ashed again with HNO3-H2O2 and dissolvedin HNO3-Al(NO3)3. Strontium is separated from matrix impurities and potentially interfering radionuclides in the sample
using stacked 2mL and 1mL cartridges of Eichrom Sr Resin. Radiostrontium is measured on a low background gas flow
proportional counter or liquid scintillation counter. Chemical yield of strontium is determined by gravimetric recovery ofstable strontium or by ICP-AES measurement. Average chemical recovery of strontium is 75 + 17%. Measured valuesof 90Sr agreed to within 3.2% and 0.5% of reference values for 20 minute count times and 60 minute count times,
respectively. The lower limit of detection for 100mL samples with 20 minute count times is 0.5Bq/L and with 60 minutecount times is 0.16Bq/L. A single operator can prepare
Figure 1. Sample Preparationbatches of 12-24 samples for 90Sr measurement in less than
8 hours.
100 mL milk
+ 50mL Water
Reagents+4mg Stable Sr Carrier
Sr Resin, 2mL Cartridges (Eichrom SR-R50-S)
Sr Resin, 1mL Cartridges (Eichrom SR1ML-R50-S)+2 mL 1.25M Ca(NO3)3
Ammonium Hydroxide (listed as 28% NH3 or 56% NH4OH)+5mL 3.2 M (NH4)2HPO4Nitric Acid (70%)
Hydrogen Peroxide (30%)
Adjust to pH 10 with NH4OH
Deionized Water
Mix Well
1.25M Ca(NO3)2
3.2M (NH4)2HPO4Strontium Carrier (10mg/mL)
Centrifuge 3500 rpm, 10 min
Decant2M Al(NO3)3
Supernate
90Sr standard
To WasteOxalic acid
Dissolve Precipitate in
20mL 3M HNO3
Equipment
Vacuum Box (Eichrom AR-24-BOX or AR-12-BOX)
Cartridge Reservoir, 20mL (Eichrom AR-200-RV20)
Centrifuge 3500 rpm, 10 min
Transfer Sr
Inner Support Tubes-PE (Eichrom AR-1000-TUBE-PE)
Supernate toYellow Outer Tips (Eichrom AR-1000-OT)
250mL Beaker
Wash Residue with50mL and 250mL Centrifuge Tubes
10-15mL 3M HNO3Centrifuge
Transfer Sr
Cupped Stainless Steel Planchets (~5mL volume)
Supernate toGas Flow Proportional Counter
Centrifuge 3500 rpm, 10 min
250mL Beaker
Muffle Furnace
Hot Plate
Analytical Balance
To Load Solution
Discard solids
250mL Glass Beakers
Preparation
to wasteVacuum Pump

Figure 2. Load Solution Preparation and Strontium Separation
Evaporate Supernate to Dryness
Wet ash with 5mL 70% HNO3
and 5mL of 30% H2O2

Muffle at 550°C for 30-60 min.
Wet ash with 5mL 70% HNO3
and 5mL of 30% H2O2
Dissolve residue in
5mL 70% HNO3 and5mL 2M Al(NO3)3(warm to facilitate dissolution)
Cool to room temperature.
90Sr(1) Precondition Sr Resin with
5mL 8M HNO3.
(2) Load sample.
(3) Rinse sample beakerwith 5mL 8M HNO3.

2mL+1mLSrResin(4) Add beaker rinse to Sr Resin.
(5) Rinse Sr Resin sequentially with:- 15 mL 8M HNO3
- 5mL 3M HNO3 - 0.05 oxalic acid- 7mL 8M HNO3
(6) Dispose of (1) to (5) as waste.
(7) Strip Sr with 13mL 0.05M HNO3.
Gas Flow Proportional Counting*:(8) Evaporate samples to dryness
on tared cupped stainless steel
planchets.
(9) Rinse Sr sample vials with 2mL
8M HNO3. Transfer vial rinse toplanchets. Evaporate to dryness.
(10) Weigh planchets on an
analytical balance to determine
gravimetric yield of stable Sr(NO3)2.

90

Sr, reference(Bq/L)
00
2.86
2.86
2.86
2.86
5.7
5.7
5.7
14.3
14.3
14.3

(11) Measure radiostrontium insamples on low background gas
flow proportional counter.
*(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). 89/90Sr canthen be measured by adding liquid
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.

Performance of Radiostrontium in Milk Method
20 Minute Count Times
60 Minute Count Times909090
Sr,measured
Sr, reference
Sr,measured
Uncertainty
Uncertainty(Bq/L)%, k = 2% Bias
(Bq/L)(Bq/L)%, k = 2
0.26
98.9
N/A
0
0.11
130
0.26
81.9
N/A
0
0.27
59
2.66
24.1
-7.0
2.86
3.09
13.2
3.96
24.7
38
2.86
3.11
16.7
3.31
20.2
15.7
2.86
2.67
13.6
2.67
18.7
-6.6
2.86
2.67
11.3
6.11
16.7
7.2
5.7
5.85
10.4
5.71
13.1
0.2
5.7
5.75
8.3
5.16
13.9
-9.5
5.7
6.04
8.2
12.8
9.1
-11
14.3
13.6
6.1
15.2
8.5
6.3
14.3
14.0
6.1
14.1
8.6
-1.4
14.3
14.2
6.1

% Bias
N/AN/A
8.0
8.7
-6.6
-6.6
2.6
0.9
5.9
-4.9
-2.1
-0.7

References1) Sherrod L. Maxwell, Brian K. Culligan, “Rapid method for the determination of radiostrontium in emergency milk
samples,” J. Radioanal. Nucl. Chem., 279(3), 757-760 (2009).
1955 University Lane Lisle, IL 60532, USA+1 (630)963-0320

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