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An appropriate combination of separation mechanisms (simultaneous use of differences in pK values, host-guest complexations, and the ionic strength dependences of the actual ionic mobilities) provided zone electrophoresis (ZE) resolution of 22 organic and inorganic acids expected in wines on a polymethylmethacrylate (PMMA) chip with integrated conductivity detection. These separating conditions offered a framework for the ZE determination of organic acids responsible for some important organoleptic characteristics of wines (tartrate, malate, succinate, acetate, citrate, and lactate). The ZE procedure developed in this context is simple and rapid (ca. 10 minutes' analysis time), while affording reproducible migration and quantitation data for the acids. For example, 0.8-2.0% RSD values characterized the migration times of the acids for 25 repeated ZE runs with the same sample carried out in 5 days in the background electrolyte solution prepared freshly on a daily basis, while 3-5% RSD values were typical for the accompanying peak area data. The concentration ranges within which the acids of analytical interest could be determined in one ZE run covered all wine samples included in our study (100-400-fold sample dilutions were needed to work under the conditions corresponding to the validities of the calibration data). 90-110% recoveries of the acids as obtained repeatedly for one of the reference wine samples used in our experiments indicate a good predisposition of the present method to provide accurate analytical results. This statement also supports the results from the determination of the acids in reference wine samples with claimed concentrations of malic (five samples), tartaric (one sample), and lactic (one sample) acids.

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This feasibility study deals with column switching in zone electrophoresis (ZE) separations on a column coupling (CC) chip. The column switching implemented into the ZE separations an on-chip sample clean up applicable for both the multicomponent and high salinity samples. In addition, complemented by different separation mechanisms in the coupled columns (channels), it provided benefits of two-dimensional separations. Properly timed column switching gave column-to-column transfers of the analytes, characterized by 99-102% recoveries, delivered to the second separation stage on the chip the analyte containing fractions contaminated only with minimum amounts of the matrix constituents. A diffusion driven transport of the matrix constituents to the second channel of the chip (due to direct contacts of the electrolyte solutions in the bifurcation region), representing 0.1-0.2% of the loaded sample constituents, was found to accompany the sample clean up performed on the CC chip. This source of potential disturbances to the separation in the second channel, however, is not detectable in a majority of practical situations. With respect to a 900 nl volume of the sample channel on the CC chip, the electric field and isotachophoresis (ITP) stackings were employed to minimize the injection dispersion in the separations and concentrate the analytes. Here, the column switching, removing a major part of the stacker from the separation system, provided a tool effective in a control of the destacking of analytes. Highly reproducible ZE separations as attained in this work also for the chip-to-chip and equipment-to-equipment frames can be ascribed, at least in part, to suppressions of electroosmotic and hydrodynamic flows of the solutions in which the separations were performed.