Combination of field amplified sample injection and hydrophobic interaction electrokinetic chromatography (FASI-HIEKC) as a signal amplification method for the determination of selected macrocyclic antibiotics.

In this study, a field amplified sample injection (FASI) and hydrophobic interaction electrokinetic chromatography (HIEKC) method has been developed for the separation of five macrolide antibiotics: spiramycin, ivermectin, tylosin, josamycin, rapamycin, and one ansamycin drug - rifamycin. By the manipulation of both the sample and separation buffer compositions, their pH values and molarity, a systematic approach has been achieved to maximize analyte differential electrophoretic mobility and signal amplification. The impact of the sample solution composition and the injection mode on the signal amplification effect of the six tested antibiotics was also investigated. Moreover, the influence of the injection of the sample and the water plug on the quantity, symmetry and height of the analyte signal was demonstrated. All the analytes were completely resolved in less than 8 min in an uncoated fused-silica capillary of 75 μm internal diameter (I.D.) x 50 cm length. The electrophoretic separations were performed in a 60% (v/v) acetonitrile and 20 mM phosphate electrolyte system (pH 7.1) with an applied voltage of 25 kV. The established method was validated and confirmed to be applicable for the determination of the active ingredients in a quality control analysis.