Isotachophoresis and isotachophoresis-zone electrophoresis of food additives on a chip with column-coupling separation channels

The use of a poly(methylmethacrylate) chip, provided with two separation channels in the column-coupling (CC) arrangement and on-column conductivity detection sensors, to isotachophoresis (ITP) and ITP-ZE separation and determination of food additives was studied. A group of preservatives and taste intensifying components examined in this study included benzoate, sorbate, p-hydroxybenzoic acid esters (parabens), and glutamate, while various food products and cosmetics represented different matrices (proteins, fat, organic acids, carbohydrates, salts). ITP on the CC chip was found suitable for the determination of glutamate in the food products with only a minimum sample preparation (dilution, filtration). It also provided a rapid and simple procedure for the determination of parabens in cosmetics. On the other hand, ITP experiments with benzoate and sorbate revealed that sample preparations providing high analyte/matrix concentration ratios are essential when these food preservatives are to be determined by ITP on the chip. ITP-ZE combination on the same chip provided a solution to this problem by integrating an efficient ITP sample preparation (concentration of the preservatives and removal of the main part of the matrix), capable of processing μL sample volumes, with a final ZE separation and sensitive detection (low μmol/L limits of detection) of the preservatives. In both ITP and ITP-ZE separations on the CC chip no interference from food matrices was found.

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