2D Capillary Electrophoresis Hyphenated with Spectral Detection for the Determination of Quinine in Human Urine

The possibilities of a column coupling two-dimensional capillary electrophoresis (2D CE) combined with fiber-based diode array detection (DAD) for the direct, highly reliable and ultrasensitive quantitative determination of quinine in real multicomponent ionic matrices (human urine) are demonstrated in this work. The capillary isotachophoresis (CITP) stage provided an on-line sample pretreatment (elimination of interfering matrix constituents, preseparation and preconcentration of the analyte) before the capillary zone electrophoresis (CZE) separation. Due to the large volume (30 µL) sample injection and CITP sample preconcentration, a simple absorbance photometric detection was sufficient for obtaining very low concentration limits of detection (∼8.6 ng/mL). The combination of the different separation mechanisms (CITP and CZE) resulted in enhanced separation selectivity. This enabled us to obtain a pure analyte zone in the directly injected real samples suitable for qualitative and quantitative evaluation. The spectral DAD allowed (i) characterization of the purity (i.e., spectral homogeneity) of the analyte zone; and (ii) preliminary indication of structurally related compounds (i.e., potential biodegradation products of quinine), via characteristic spectra recorded in intervals of 200-800 nm. The CITP-CZE-DAD method was characterized by favorable performance parameters that are suitable for its routine biomedical use. One of the primary benefits of the CITP-CZE-DAD method is the possibility of performing direct injections of real biological samples while avoiding external sample preparation procedures and, therefore, enhancing the reliability and applicability of analyses and the potential for method automatization and miniaturization.