EFFICIENT ANALYSIS OF NEUTRAL AND HIGHLY POLAR PHARMACEUTICAL COMPOUNDS USING REVERSED-PHASE AND ION-EXCHANGE ELECTROCHROMATOGRAPHY

Highly polar compounds, such as tricyclic antidepressants are very dif ficult to analyse by electrochromatography with conventional reversed- phase silica-based chromatography packings. At high pH (high electroos motic flow) the test compounds were not eluted from a Spherisorb ODS-1 column, as a result of strong interactions between the analyte and re sidual silanol groups on the packing material. By lowering the pH of t he mobile phase, whereby the highly basic test compounds become positi vely charged, it was possible to elute the samples but only with sever e peak tailing. Because the electroosmotic flow was greatly reduced, t he elution time for neutral species became prohibitively long. By use of a strong cation exchanger in place of C-18-silica it was found poss ible to resolve a series of highly basic compounds with very high effi ciencies, with very little evidence of peak tailing. Plate numbers in excess of 8 million per metre were observed.