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The fluorescence quenching of TGA-CdSe quantum dots (QDs) was used for Cr(3+) quantification in vitamin supplements. The QD was electrochemically synthesized, demonstrating high reproducibility with control of particle size, thus making it a clean method, without the presence of reducing agents. Under ideal conditions, with the fluorescence band at 551 nm (excitation 365 nm), the maximum fluorescence quenching was observed at pH 4.0, with a time of 200 s for each data acquisition. Under optimum experimental conditions, linear quenching was observed for Cr(3+) in the range of 25.0-325.0 ng L(-1) (R=0.9996, n=6), a limit of detection of 5.67 ng L(-1), and relative standard deviation of 4.43% (n=10). The recovery test for Cr(3+) quantification in vitamin supplements presented results from 82% to 98%. These Cr(3+) determination results were compared to the same vitamin supplement sample using flame atomic absortion spectrometry (FAAS) method, and no significant differences were observed at 95% confidence level.

A multicommuted flow procedure for the spectrophotometric determination of reducing sugars in wine has been developed. A dialysis unit was incorporated in the system to minimize matrix interferences and eliminate the colored compounds of the wine. The oxidation-reduction reaction in an alkaline medium between reducing sugars and the Cu 2+ -Neocuproine complex was employed. The compound formed was monitored at 460 nm. In the proposed procedure, there was a linear response between 0.25 and 4.0 g L -1 reducing sugars (y = (0.36 ± 0.02) + (0.31 ± 0.01) * x, R = 0.9975, n = 6), a coefficient of variance of 2.6% for a reducing sugar solution of 2.0 g L -1 (n = 7), a limit of detection estimated at 0.03 g L -1 , reagent consumption per determination of 0.330, 0.128 and 0.160 mg for neocuproine, CuSO 4 and NaOH, respectively. A sampling throughput of 45 determinations per hour was achieved. The proposed system was applied to wine samples and comparing the results with an AOAC official method no significant difference at a 95% confidence level.

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