Isotachophoresis as a preseparation technique for liquid chromatography

High-performance liquid chromatographic (HPLC) profiles of uremic serum ultrafiltrate are rather complex [l] . For purposes of identification and characterization of the HPLC peaks, information may be obtained from chromatographic retention data, on-line and off-line HPLC-mass spectrometric analysis, off-line (Fourier) infrared analysis and to a certain extent from UVratio monitoring at multiple wavelengths [2]. However, it is desirable to decrease the complexity of the profiles, especially in view of the spectrometric identification techniques, where peak impurities might obscure the spectra. For this reason uremic serum ultrafiitrate was preseparated by isotachophoresis [3], the advantages of which are as follows. (1) The concentration effect of dilute samples. (2) The self-sharpening effect of zone boundaries. (3) The possibility of selecting a discrete amount of anions or cations by a proper choice of electrolyte conditions. (4) The length between leading zone and terminating zone (sample) is constant at the moment the terminator has passed the injection point. The steady-state therefore need not to be reached for sample collection. (5) Using valves for sample introduction even allows the collection of non-ionic compounds, as they remain in the valve during the isotachophoretic separation.