Simultaneous separation of 12 different classes of antibiotics under the condition of complete protonation by capillary electrophoresis-coupled contactless conductivity detection.

A novel capillary electrophoresis - capacitively coupled contactless conductivity detection (CE-C4D) method for the separation of 12 antibiotics, including four types of aminoglycosides, three types of fluoroquinolones, two types of tetracyclines, and three types of macrolides, was developed. Half of these antibiotics were not determined by ultraviolet (UV) because of their lack of UV-absorbing groups. Formic acid (FA) (pH 2.50) with low conductivity was employed as the background electrolyte (BGE) in comparison with three BGE systems (i.e., HAc, HCl and H3PO4), which not only allowed complete protonation and electrophoresis separation but provided more cost-effectiveness and shorter analysis time. Under these conditions, a UV detector was employed as an additional detection mode to evaluate the qualitative analysis of 6 antibiotics possessing UV absorbing groups. Moreover, it was found that the sensitivities of the C4D and UV detectors were similar. Albeit a slightly reduced sensitivity of C4D in the analysis of norfloxacin, enrofloxacin and tylosin compared to UV, enough points were achieved to detect all analytes by C4D. The repeatability with respect to peak areas and migration times was better than 4.69% and 2.48% (n = 5), respectively. Mixed liquid pharmaceutical formulations of tobramycin eye drops having non-UV absorbing groups and ofloxacin eye drops possessing UV absorbing groups have been separated and detected in a single run by this technique. The studied recoveries of the two were 100% and 103%, respectively.