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

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Abstract

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.

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    These values are still more than acceptable, however, for the development of any kind of immunological method. A comparison of the main analytical data referring to penicillin G analysis, obtained using both the present immunosensor and ion selective electrodes (ISEs) investigated in previous research by the present and other authors [29,30] and by enzyme sensors [31–44] or immuno-devices developed by other authors [45–53], is shown in Table 7. The lower detection limit is 10−10 M for the present immunosensor, about 10−4 or 10−5 M usually for most of the penicillinase enzymatic sensors and about 10−4 M for most of the ISEs responsive to penicillin G.

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Present address: Draco AB, P.O. Box 34, S-221 00, Lund, Sweden.

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