An automatic determination of caffeine in soft drinks using flow injection system with amperometric detection

An automatic procedure based on a flow injection analysis manifold has been developed for the determination of caffeine in soft drinks using amperometric detection (+1.70 V vs AgCl/Ag). The sample and standards were injected without pre-treatment, with a sampling rate of 120 determinations per hour. The determination of caffeine in several soft drinks available in Portugal using the developed automatic system provided results with mean recovery values between 98% and 103% and a mean standard deviation between 2% and 5%. The results obtained were compared with those given by the reference method recommended by AOAC. Relative deviation was always less than 4%. Reproducibility of the method was assessed by the relative standard deviation (RSD%), values of which were less than 2%.