Determination of organic acids and inorganic anions in wine by isotachophoresis on a planar chip

Isotachophoretic (ITP) separation and determination of a group of 13 organi c and inorganic acids, currently present in wines, on a poly(methyl methacr ylate) chip provided with on-column conductivity detection was a subject of a detailed study performed in this work. Experiments with the ITP electrol yte systems proposed to the separation of anionic constituents present in w ine revealed that their separation at a low pH (2.9) provides the best resu lts in terms of the resolution. Using a 94 mm long separation channel of th e chip, the acids could be resolved within 10-15 min also in instances when their concentrations corresponded to those at which they typically occur i n wines. A procedure suitable to the ITP determination of organic acids res ponsible for some important organoleptic characteristics of wines (tartaric , lactic, malic and citric acids) was developed. Concentrations of 2-10 mg/ l of these acids represented their Limits of quantitation for a 0.9 mul vol ume sample loop on the chip. A maximum sample load on the chip, under the p referred separating conditions, was set by the resolution of malate and cit rate. A complete resolution of these constituents in wine samples was reach ed when their molar concentration ratio was 20:1 or less. ITP analyses of a large series of model and wine samples on the chip showed that qualitative indices [RSH (relative step height) values] of the acids, based on the res ponse of the conductivity detector, reproduced with RSD better than 2% whil e reproducibilities of the determination of the acids of our interest chara cterized RSD values better than 3.5%. (C) 2001 Elsevier Science B.V. All ri ghts reserved.