Evaluation of a multiple-variable thin-layer and reversed-phase thin-layer chromatographic scheme for identification...

An analytical scheme composed of one normal-phase thin-layer chromatographic (TLC) method, one reversed-phase thin-layer chromatographic (RPTLC) method, and sequential analyte detection through four stages of color reactions is described. Eighty-one basic or neutral drugs were analyzed with this scheme and seventy-four were uniquely characterized with 95% confidence. Six of the remaining seven formed three unresolved pairs. The scheme was evaluated by mean list length analysis and shown to offer analyte resolution similar to that of a scheme of TLC and gas chromatography (GC) with nonspecific detection. Nine out of ten unknowns from the field of eighty-one drugs were uniquely identified with 95% confidence by the TLC/RPTLC scheme. The tenth unknown was not completely resolved from its isomer, but was statistically the more probable candidate.