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1. Use a 15 cm3centrifuge tube and add
   • 3 cm3carrier-free 32P soln
   • 1 cm3 deionised H2O
   • 3 drops 3 M sulphuric acid
   • 4 drops 10% ammonium molybdate
2. Cap the tube and mix thoroughly, then add 3 cm3 ethyl acetate
3. Recap the tube and shake vigorously for 2 min
4. Centrifuge at 5000 rpm for 5 min to separate the 2 layers and note the volume of each
5. Pipette out 0.5 cm3 of the organic phase (top layer) and put into a planchette
6. Carefully remove rest of the organic phase and discard into waste beaker provided
7. With a clean pipette take 0.5 ml of the aqueous layer and put into a 2nd planchette
8. Dry both under an infrared lamp. Note that the organic phase must be dried very slowly to avoid creepage
9. When nearly dry, add 4 drops of 6 M ammonium hydroxide to neutralise the acid
10. Complete the drying
11. Count both sources on a Geiger counter
12. Repeat the expt using varying carrier concentrations in place of the 1 cm3 deionised H2O. The carrier soln is orthophosphoric acid which is supplied at 10 mg cm-3. In each case adjust the total volume of the carrier solution to 1 cm3 using distilled water.
    • 0.5 mg cm-3
    • 1.0 mg cm-3
    • 5 mg cm-3
    • 10 mg cm-3

Results

The distribution ratio and the percentage extracted should be calculated for each extraction system. If enough results are available these may be presented graphically to show the dependence on the initial phosphate concentration in the aqueous layer.