METHOD DEVELOPMENT AND VALIDATION PROCEDURE FOR THE CHROMATOGRAPHIC ASSAY OF COCAINE AND ITS METABOLITES IN PHARMACOKINETIC STUDIES

Although chromatographic assay is one of the most powerful methods of analysing cocaine and its metabolites in blood samples, the methods presently available for the separation of the metabolites suffer from problems with long-term use for large numbers of assays. We describe the development of a method and devote special attention to the description of the validation procedures of each step of the assay. The validation procedures can be described in two parts. The first is the development of the separation by reversed phase HPLC using the retention properties of cocaine and its major metabolites norcocaine, benzoylecgonine, norbenzoylecgonine as affected by the strength, selectivity and pH of the mobile phase. On a C18, end-capped column, on-column band broadening was limited to the extent that all pairs of peaks are resolved. Extraction from plasma was performed with C18 Bond-Elut and good recovery obtained, without interferences, for all the products under study (cocaine recovery 90.9 +/- 6.3 %). The internal standard method using atropine has been used for the assay. Validation procedures enabled quantification of cocaine and its main metabolites at concentrations between 50 and 2000 ng/ml.