Abstract

INVESTIGATION ON ENZYMATIC DEGRADATION OF AMPICILLIN AND AMOXICILLIN IN AQUEOUS SOLUTION

Lixin Li and Hanwen Sun*

ABSTRACT

The enzymatic degradation of ampicillin and amoxicillin in aqueous solution was investigated by ultra-performance liquid chromatography coupled with electrospray ionization-time-of-flight mass spectrometry. The influence factors on the degradation were investigated, including β-lactamase dosage, temperature, time, and acidity. Their degradation products and the isomers of ampilloic acid and amoxilloic acid were identified based on the accurate mass and a sub-structure of the penicillins. The effect of pH and temperature on enzymatic degradations and degraded products of ampicilloic acid and amoxicilloic acid is stronger than on chemical acid hydrolysis. The proportion of the degradation products (ampicilloic acid and ampilloic acid; amoxicilloic acid and amoxilloic acid) was different with temperature and pH. When the temperature increased from 40 to 70°C, the proportion of the both penicilloic acid decreased markedly, up to near zero, it suggests the proportion of ampilloic acid and amoxilloic acid increased up to near 100% under 60‒70°C because the decarboxylation of the penicilloic acids formed penilloic acid. It is suggested that ampilloic acid and amoxilloic acid may be used as a standard for reliable quantitative analysis.

Keywords: Ampicillin; amoxicillin; degradation; ?-lactamase.