Rapid determination of majority cations in yoghurts using on-line connection of capillary electrophoresis with mini-dialysis

•On-line connection of capillary electrophoresis with midi-dialysis.•High speed separation by electrophoresis in short capillary.•Flow-gating interface with sampling space filled with air during injection.•Rapid sample preparation by digestion in hot acid.•Laboratory made portable analytical instrument with low first and operating cost. An analyser was constructed on the basis of on-line connection of capillary electrophoresis over a short separation path with continuous mini-dialysis sample collection. The developed instrument was employed for simultaneous determination of the majority minerals K+, Ca2+, Na+ and Mg2+ (and possibly NH4+ ions) in commercially available unflavoured yoghurts. The cations are released from the organic structures by digestion with boiling 6 mol/L HCl. They were separated from residues of the organic matrix by a dialysis probe and were transferred to a stream of water. From the continuous stream, the dialysate was injected into the separation capillary through a flow-gating interface. Within the reliability interval, the determined total mineral content was equal to their contents stated on the yoghurt labels and the content determined by flame atomic absorption spectrometry and complexometric titration. The relative standard deviation of the electrophoretic determination is mostly about 5%.