Experimental
1. You have been given a solution containing phosphate & chloride, which also contains 3.7 kBq per 1cm3 of 32P

2. Pipette 0.5 cm3 to an aluminium planchette and evaporate under the infrared lamp in the fume hood. Handle the planchette with tweezers and transfer to the fume hood on a tray.

3. Once completely evaporated add another 0.5 cm3 and evaporate

4. Repeat until a total of 2 cm3 have been evaporated

5. Cover the planchette with sellotape and count on shelf 2 of a Geiger counter for 100 sec

6. Remove the planchette and measure the background count for 100 sec

Precipitation Methods
1. Take 2.5 cm3 of the phosphate/chloride solution and place in a boiling tube

2. Add 1 cm3 concentrated nitric acid and 5 cm3 of distilled water

3. Warm to approximately 80 °C in the dry bath in the fume hood

4. Measure out 3.8 cm3 of 10 % neutral ammonium molybdate into a 15 mL centrifuge tube and add 1 g ammonium chloride

5. Once the phosphate/chloride soln is warmed, transfer to the 15 mL centrifuge tube

6. Leave to stand at room temp. A precipitate of ammonium molybdophosphate will form after about 30 minutes

7. Centrifuge at 5000 rpm for 5 minutes

8. Pour off supernatant into a clean tube and retain

9. Transfer approximately 20 mg of this precipitate onto an aluminium planchette and dry under the infrared lamp. Do not do this for no more than 30 seconds at a time due to the risk of it catching fire.

10. Reweigh the tray and if the precipitate has reached a constant weight, cover with sellotape and count in the Geiger counter. If the weight is reducing, repeat the drying step until it is constant.

11. Calculate the weight of disodium hydrogen phosphate in the original solution assuming the precipitate to be (NH4)3PO4.12MoO3 as described previously

12. Evaporate 2 cm3 of the supernatant on another planchette in 0.5 increments, cover with sellotape and count.