DESIGN AND APPLICATIONS OF A NEW FLUOROMETRIC ASSAY OF THIOGUANINE INLIPOSOMES

This paper describes the systematic design of a modification that over comes the difficulties encountered with the original fluorimetric meth od for thioguanine. It allows the determination of thioguanine alone, as well as in a lipid medium (specifically in liposomes). It consists of an earlier lipid extraction based on liquid-solid extraction cartri dges; then the oxidation of thioguanine in the lipid-free solution is performed by adding hydrogen peroxide in pH 4.7 acetate buffer at 50 d egrees C for 30 min. A central composite design was used to finally op timize the method. The assay is precise (RSD values were 1.8 and 2.1% for intra-day and between-day precision, respectively). The detection limit was 0.05 mu M and the limit of quantitation 0.08 mu M.