Radiochemical quenching

Figure 7.8. Quenching effect of 5 mL rat plasma, following protein precipitation, on radiochemical signal using Scintiplate approach (a) [14C] (b) pH].

To a solution of perillyl alcohol (34, 91,2 mg, 0.6 mmol) in anhyd CHCl, (0.5 mL) was added a solution of TCHIj (9 mCi, 0.23 mmol) in CDClj (0.5 mL) and stirred for 5 min. 1 M i-BujAI in toluene (2mL) was added and the mixture stirred at rt for 3 h. The reaction was quenched by the addition of CHClj (5 mL) followed by excess NaF and HjO (2 mL). The CHCl, layer was separated, dried and evaporated to give the product for NMR and radio-HPLC analyses. HPLC purification afforded 3 mCi of the cyclopropane derivative which represents a radiochemical yield of 33%. 

An aqueous sample may be added to the cocktail directly, after minor prior processing, or at the end of a radiochemical separation procedure. Direct addition is the equivalent of gross activity counting discussed in Section 7.2.4 except that some spectral analysis may be possible. Alpha particles can be differentiated from beta particles by deposited energy, pulse shape, and decay time. Self-absorption is of no concern. Quenching and luminescence, discussed in Section 8.3.2, often occur. Identification by maximum beta-particle energy is approximate, and requires comparison to radionuclide standards. 

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