Determination of 90-Sr from Milk Powder

Lab Exercise - Determination of 90Sr from Milk Powder

Developed By

Laboratory of Radiochemistry
Department of Chemistry
University of Helsinki

Learning Goals

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Explanation and Exercise Guide


Milk Powder and Strontium (read)

Experimental Procedure

1. Weigh out 10 g milk powder ash into a 400 mL beaker.

2. Add 3 mL (30 mg) Sr carrier solution (10 g/L), 200 mL distilled water, 40 mL 65 % nitric acid (HNO3).
Heat ash-bearing solution to boiling on an electric heater and filter hot solution through a wetted filter paper into a 600 ml beaker.
The deposit on the filter is discarded.
Add 3 mL 85 % phosphoric acid (H3PO4) into the filtrate.
Add 25 % Ammonia (NH3) until the pH of the solution is about 10.
Pour the phosphate precipitate -bearing solution into centrifuge tubes, is centrifuge and discard solution. The precipitate is washed twice with a solution containing 15 mL 25 % NH3 + 1,5 ml 85 % H3PO4) in one litre of deionized water. Centrifuge after washing and discard solution

3. Dissolve the precipitates in the centrifuge tubes with a small amount of 65% nitric acid and combine the solutions. Evaporate to near dryness and dissolve the residue in 20 mL of 8 M nitric acid.

4. Preparation of SrResin column (Eichrom/Triskem offers also prepacked 2 mL and 10 mL SrResin column, when using them packing is not necessary)
Put a small piece of fiberglass on the bottom of the column.
Fill the column to half with water.
Weigh 3 g of SrResin (100-150 µm) and stir it into a small volume of distilled water.
Transfer the resin-water mixture with a disposable pipette into the column.
Put a small piece of fiberglass on the top of the column.
Rinse the column an excess of water – keep the water table on the top of the upper fiberglass.
Rinse the column 30 mL of 3 M HNO3.

5. Pour the sample solution into the column and let it freely drop into a underlying beaker.

6. Rinse the SrResin column by
twice with 20 mL 8 M HNO3
once with 20 mL 3 M HNO3
Write down the time when the last rinsing is finished since 90Y out elutes from the column.

7. Elute strontium out of the column with 70 mL 0.05 M HNO3, collect the eluate into a 250 mL baker (high) and make the solution alkaline (pH 8-9) with 25 % NH3.
Precipitate strontium carbonate by adding 3.5 - 4 g solid ammonium carbamate (NH4CO2NH2).
Heat the solution on a water bath until a fine-grained deposit has settled down on the vial bottom.
Let the solution cool on an ice bath.

8. Filter the SrCO3 precipitate through a Millipore filter holder with suction on the Ø 25 cm filter paper.
Wash the precipitate three times with 5 mL of dist. H2O and additional three times with 5 mL of technical ethanol.
Dry the precipitate for 10 min. at 105 OC in oven, let cool in a desiccator.
Transfer the precipitate into a 20 mL LSC vial (weighed five times - take average value)
Weigh five times - take average.

9. Dissolve the precipitate in 2 mL of 1 M HCl. Mix carefully.
Add 18 mL of HiSafe 3 liquid scintillation solution. Mix carefully.
Let the sample stand for two weeks in a cool place. Within two weeks 90Y grows up in equilibrium with 90Sr.

10. Prepare a sample from a 90Sr/90Y standard solution, in which 90Sr and 90Y are in equilibrium.
Take about 2 Bq of 90Sr/90Y standard solution and add it into a mixture 2 mL 1 M HCl + 18 mL HiSafe 3 in a LSC vial. Mix carefully.

11. Prepare a background LCS sample containing 2 mL 1 M HCl + 18 mL HiSafe 3 in a LSC vial.

12. Measure the 90Sr+90Y activity of the unknown, standard and background samples with
the liquid scintillation counter.

Questions for the Students


Describe in detail the whole separation procedure and explain why each step was made. Draw a separation procedure scheme.

Calculate the chemical yield from the masses of the vial, vial with the precipitate and the added carrier.

Calculate the activity concentration of the milk powder ash and its uncertainty.

mfilter paper ....................... (mean of 5 measurements)

mfilter paper +precipitate........................... (mean of 5 measurement)

mSr carrier .............................

AStd ............................. ,ref. date .....................


Safety Aspects

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Preparation for the lab Supervisor

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Feedback from Users and Supervisors

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