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A mesofluidic platform (MP) with fluorescence detection based on a stepwise injection analysis (SWIA) was used for the determination of curcumin in biologically active supplements and food spices. The main units of the MP are a mixing chamber (MC) and an optical channel with a quartz capillary inside. The MC provides rapid and complete mixing solutions by gas bubbling. The proposed method is based on the new rapid and sensitive reaction of curcumin with a fluorescence reagent – 4-(2,3,3-trimethyl-3H-indolium-1-yl)butane-1-sulfonate (TIBS). The fluorescence intensity of TIBS is greatly quenched in the presence of curcumin in an alkaline medium. The linear range was from 1 to 10 µM of curcumin, and the limit of detection, calculated as 3σ of a blank test (n=5), was found to be 0.3 µM. The sample throughput was 24 h−1. The proposed method was successfully applied for the determination of curcumin in biologically active supplements and samples of food spices. The obtained data were in good agreement with those measured by a HPLC-UV method.

A procedure is developed for the flow-injection spectrophotometric determination of cysteine in dietary supplements based on the formation of a reduced phosphomolybdic complex by the analyte in mixing a sample solution with a solution of ammonium 18-molybdophosphate. For the flow-injection determination of cysteine, a polymethyl methacrylate chip is fabricated, in the channels of which the analytical form was obtained and detected. The detection limit for cysteine is 3 × 10–6 M and the throughput is 240 determinations per hour. The procedure was tested in the analysis of different samples of dietary supplements; the results obtained were verified by HPLC.

A stepwise injection analysis system was developed to monitor the concentration of l -cysteine in biologically active supplements (BAS) and fodders. It is based on the rapid redox reaction of l -cysteine with 18-molybdo-2-phospahte heteropoly anion (18-MPA) and the detection of the formed heteropoly blue with a spectrophotometry. The method has relatively wide optimal ranges of pH and 18-MPA concentration − 5.0 to 7.3 and 0.4 to 2.0 mM, respectively. Under optimized operating conditions the performance of the SWIA system was linear up to a concentration of l -cysteine of 0.1 mM ( R 2 = 0.994) with a detection limit of 0.003 mM and a sample frequency of 20 h − 1 . The SWIA system was employed to determine the concentration of l -cysteine in BAS and fodder. The obtained data were in good agreement with those measured by a HPLC method.