Long-term analyses in automated electrophoretic analyzer in hydrodynamically closed separation system

•On-line combination of cITP–CZE in automated electrophoretic analyzer.•Some potential problems occurring during the long-term analyses of samples.•Stability study of some basic analytical parameters (precision, accuracy).•Analyses of different kinds of the analytes and the samples.

Some potential problems that can occur during the analyses of complex samples by on-line combination of capillary isotachophoresis–capillary zone electrophoresis (cITP–CZE) in automated electrophoretic analyzer with the column-coupling configuration of the separation unit were studied in this work. The main focus was devoted on the reproducibility of important analytes’ parameters (migration time, peak height and peak area) and also on the stability studies of selected low and high molecular mass analytes of inorganic/organic origins (bromate, vitamins, proteins) present at low concentration levels in different kinds of matrices (mineral water, human urine).Such study was carried out for the first time for the electrophoretic analyzer operating in the hydrodynamically closed separation system provided with contact-less conductivity detectors and UV detector in CZE step. Hydrodynamic and electroosmotic flows of the buffer solutions were suppressed and therefore, only the electrophoretic transport of ions was significant. Obtained results showed the different stabilities of the analytes and samples depending on their origin. The focus in the long-term analyses should be paid on the storage of the samples and on the regular changing the contents of electrolyte vessels to keep the electrolyte composition and separation conditions as constant as possible.