Flow-injection analysis for the measurement of penicillin V in fermentation media

Abstract

Three different flow-injection analysis systems for measuring penicillins in complex fermentation media were tested: a molybdenum blue, an iodimetric and a potentiometric method. All the methods are based on enzymatic hydrolysis of the penicillin to the corresponding penicilloic acid using β-lactamase, followed by detection of penicilloic acid. The β-lactamase is immobilized in a packed-bed reactor in which there is 100% conversion of penicillin to penicilloic acid, and all the methods therefore measure the sum of penicilloic acid and penicillin in the sample. The iodimetric method was found to be the best method for measurement in fermentation media. By replacing the enzyme reactor with an enzyme-free dummy reactor, it is possible to measure the concentration of penicilloic acid alone, and thence the penicillin concentration can be determined by subtraction of the penicilloic acid concentration from the total response in the analyser with the enzyme reactor inserted. The application of the analyser was tested by monitoring a fed-batch penicillin fermentation and the correlation between measurements by the FIA system and a liquid chromatographic method was very good.