A flow-injection system based on immobilized penicillinase and a linear pH-buffer for potentiometric determination of penicillin

Penicillin is determined in a flow-injection manifold by hydrolysis of the β-lactam ring by means of an on-line reactor containing immobilized penicillinase with detection of the produced acid by a glass electrode. The penicillin concentration is calculated as the difference in response between a sample passing through the enzyme reactor and a sample flowing directly to the glass electrode. The pH signal is made linearly dependent on the acid concentration by using a buffer mixture of constant buffer capacity and the reactor is designed so that hydrolysis of the penicillin is essentially complete in the reactor. The linear range is 0.1–15 mM penicillin and the sensitivity is 0.056 pH mM^?1. The sample throughput is 60 h^?1 and the relative standard deviation < 1%. The proposed method is primarily intended for the analysis of purified potassium salts of penicillins in pharmaceutical preparations.