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The capillary electrochromatographic (CEC) separation of a range of pharmaceutical bases was investigated on a commercially available silica stationary phase using aqueous mobile phases. The effects of mobile phase composition, buffer pH, applied voltage, and buffer anion on the retention behaviour of these bases were studied. Promising chromatography was obtained at pH 7.8 but was later found to be irreproducible. However, successful and reproducible chromatography of the bases was achieved at pH 2.3. We have previously demonstrated that the addition of mobile phase additives such as TEA-phosphate at low pH values has resulted in excellent CEC analysis of bases on reversed-phase packing materials. The same approach was applied to the analysis of bases on the silica phase in order to improve peak shape. Excellent chromatography was obtained for the analysis of strong pharmaceutical bases such as benzylamine, nortriptyline and diphenhydramine. The experimental investigations have shown that the CEC separation of a range of pharmaceutical bases can routinely be achieved with excellent peak shapes and peak efficiencies as high as 320,000 plates m 1.

Abstract:The capillary electrochromatographic separation of six substituted barbiturates in the ion-suppressed mode was investigated on commercially available C18, C8, and, phenyl-bonded packing materials. The effect on the retention behavior of mobile phase composition, buffer pH, buffer ionic strength, and temperature was studied. Successful chromatography of the barbiturates was achieved with all three packing materials over a pH range from 2.3 to 7.8. It was Ž . notable that a significant electroosmotic flow EOF was generated with a pH 2.3 mobile phase for all the packing materials, suggesting that capillary electrochro-Ž . matography CEC in the ion suppression mode can be applied to a wide range of weakly acidic compounds of pharmaceutical interest. The C18, C8, and phenylbonded packing materials gave similar selectivities and retention times, and approximately linear relationships between percentage organic modifier in the mobile phase or temperature versus ln k were observed. Increasing the buffer ionic strength reduced the EOF but did not result in changes in selectivity. The use of methanol compared with acetonitrile had no effect on selectivity but resulted in a large increase in retention of the analytes. The experimental investigations have shown that the CEC separation of a series of weakly acidic compounds of pharmaceutical relevance can be achieved readily using a range of commercially available packed capillaries.

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Capillary electrochromatography (CEC) is a new and exciting hybrid separation technique that seeks to exploit the combined advantages of both capillary electrophoresis (high efficiencies) and HPLC (mobile and stationary phase selectivity). It is a technique with tremendous potential, especially in the pharmaceutical and biomedical fields. This is the first book to be devoted to the topic and presents reviews by the world leaders in the field on the theory and development of the technique and current and potential future applications. Capillary Electrochromatography provides an excellent introduction to the field for graduates and professionals in industry and academia with an interest in separation science.