On-line Flow Injection–Pervaporation of Beer Samples for the Determination of Diacetyl

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Abstract
A method for the determination of diacetyl based on the integration of a continuous pervaporation module and a flow injection manifold is presented. The chemical derivatization reaction involes condensation between diacetyl, α-naphthol and creatine in a basic medium to form a coloured compound, which is monitored photometrically at 530 nm. The method affords low detection and quantification limits (5 and 10 ng ml - 1 of diacetyl calculated as ±3ς and ±10ς, respectively, for n = 20), a wide linear range (10–2000 ng ml - 1 , r 2 = 0.9998, n = 7), good precision (RSD <3%) and a sampling frequency of 8 h - 1 . The method was applied to the determination of diacetyl in beer from bottled and medium-process samples and the results were in excellent agreement with those given by the conventional method.

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