High-performance liquid chromatographic separation and electrochemical detection of penicillins

Chromatographic analysis of penicillins in pharmaceutical formulations and biological fluids

Natural penicillin (benzylpenicillin) is the oldest antibiotic observed by Alexander Fleming in 1928. To broaden its spectrum of activity, natural penicillin was modified, giving rise to a group of antibiotics under the name 'penicillins'. Although an increasing number of bacteria appear to be resistant to them, penicillins are used to treat a variety of bacterial infections including Gram-positive, Gram-negative aerobic and anaerobic bacteria. Consequently, they are widely used in human and veterinary medicine to prevent and treat diseases. This review covers the analytical methodologies, mainly chromatographic, employed to the penicillins determination in pharmaceutical formulations, biological fluids and in production-scale fermentations reported in the literature. Results of published assays are comparatively presented focusing on sample preparation regarding isolation and purification, chromatographic conditions and method validation. Information on chemical structure, spectrum of activity and action mechanism of common penicillins has also been given.

Electrochemical behavior and differential pulse polarographic determination of piperacillin sodium

In an aqueous piperacillin sodium solution, a well-defined single wave or single peak was observed by direct current (DC) polarography or differential pulse polarography (DPP). The peak potential change per pH unit was -54 mV in the phosphate buffer at 18 degrees C, which indicated that protons were involved in the electrochemical reduction of the 2,3-dioxopiperazine moiety of piperacillin sodium with a H+/e- ratio of one. Using a phosphate buffer of pH 4.3, the 1.0 x 10(-7) M piperacillin sodium single peak could be determined by DPP with relative standard deviation of 1.6% (n=3). Piperacillin sodium could be analyzed without interference from penicillin G-potassium, which enabled the employment of DPP as a fast and simple technique for monitoring the synthetic process of the antibiotic.

High-performance liquid chromatographic separation and electrochemical detection of cephalosporins

Pulsed amperometric detection (PAD) is useful for detection of cephalosporins following separation on a C18 column using an acetate buffer solvent with a small percentage of organic modifier. Under these conditions, the indirect PAD mode worked better than direct PAD, with IPAD outperforming both. A gradient program was demonstrated that allowed separation and sensitive electrochemical detection of eleven different cephalosporins with widely differing side chain structures. The cephalosporins could be detected to sub-micromolar levels with this separation. Applications of the method for quantitation of pharmaceutical formulations and for monitoring cephalexin in porcine serum were demonstrated. To improve the detectability of cephalexin, an on-column concentration scheme using separate concentration and elution solvents was applied to porcine serum.

Assay for cephapirin and ampicillin in raw milk by high-performance liquid chromatography--integrated pulsed amperometric detection

The FDA has issued guidelines governing the use of antibiotics in cattle and routinely tests for the presence of antibiotics in milk. Unfortunately, these compounds are often difficult to detect by direct methods because they often lack a chromophore or fluorophore. Integrated pulsed amperometric detection (IPAD) following reversed-phase liquid chromatography is well-suited for this analysis because it is selective, sensitive, and direct; i.e., derivatization is not required. This work involves the development of a simple, rapid assay for the determination of beta-lactam antibiotic residues in milk using HPLC-IPAD, specifically, ampicillin and cephapirin. Since the analyst studied here are detectable by UV detection, a comparison between IPAD and UV detection will be made. Sample preparation schemes that involve the extraction of antibiotics of interest from the milk matrix and subsequent cleanup are an important aspect of this project. These procedures will be discussed in detail. In addition, analytical figures of merit and IPAD wave form optimization will be addressed.