Simultaneous determination of β-lactamic antibiotics by a new high-performance low-pressure chromatographic system using a multisyringe burette coupled to a monolithic column (MSC)

A technique based on multisyringe chromatography (MSC) was developed to determine three beta-lactamic antibiotics. Amoxicillin (AMOXI), ampicillin (AMPI) and cephalexin (CEPHA) were analyzed using a system with a very simple design and very low-cost equipment consisting of a multisyringe module, three low-pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometric detector monitoring at 250 nm. Mobile phases containing methanol:acetic acid (0.1 M)-sodium acetate (0.1 M), pH 6.2, were tested for various ratios of methanol:acetic acid-sodium acetate, but a ratio of 10:90 gave optimum results with a flow rate of 2 ml min(-1). Validation parameters were evaluated for amoxicillin. The response to amoxicillin was linear over the range 0.04-0.4 mg/mL, with a correlation coefficient of 0.9996; precisions, evaluated as the repeatability for 0.04, 0.16 and 0.4 mg/mL amoxicillin, were 0.6%, 0.1% and 0.6%, respectively. Recovery from a generic formulation of amoxicillin was evaluated. The method showed selectivity in the presence of excipients commonly used in capsules, and satisfactory specificity was observed for amoxicillin and hydrolytic degradation products. The linearity was also evaluated for cephalexin and ampicillin. The conditions selected for MSC separation were compared with those for a HPLC system, and similar results were obtained in terms of chromatographic parameters but a difference in retention times was observed.