On-line flow injection-pervaporation of beer samples for the determination of diacetyl

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, alpha-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 +/-3 sigma and +/-10 sigma, respectively, for n = 20), a wide linear range (10-2000 ng ml(-1), r(2) = 0.9998, ii = 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.