SEPARATION OF TETRACYCLINES BY HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS AND CAPILLARY ELECTROCHROMATOGRAPHY

Separations of various tetracycline mixtures by high-performance capil lary electrophoresis (HPCE) and a new form of electrochromatography (C EC) are compared. The new CEC method involves etching the inner wall o f the capillary surface with an appropriate reagent (ammonium dihydrog en fluoride) in order to produce a significant increase in surface are a. The etched surface is then modified by a silation/hydrosilation rea ction sequence to first produce a hydride intermediate which is then f urther reacted to attach a C-18 moiety. The bare and hydride capillari es are tested under HPCE conditions while the C-18 capillary functions in the CEC mode. The effects of pH and the presence of an organic mod ifier (methanol) are also studied. Detection limits (<10 mu g/ml) are comparable to previous HPLC and HPCE results. Resolutions for mixtures which simulate real analytical problems are equal to or better than t hose reported for separations on polymeric and diol columns by HPLC an d in earlier studies by HPCE and MECC.