Field-amplified sample injection coupled with pseudo-isotachophoresis technique for sensitive determination of selected psychiatric drugs in human urine samples after dispersive liquid-liquid microextraction

A field-amplified sample injection (FASI) technique was elaborated for fast and sensitive determination of selected central nervous system drugs in human urine samples. Factors affecting the sensitivity enhancement, such as background electrolyte (BGE) and the analytical matrix composition were optimized and discussed. Pseudo-isotachophoresis (p-ITP) mechanism contribution in preconcentration mechanism was discussed. All separations were performed in uncoated fused silica capillaries 50 μm × 57 cm at 22 kV. The optimized analytical matrix was composed of 0.25 mM HCOOH in 90% (v/v) methanol, while BGE contained 45 mM TRIS/HCl (pH 2.20). The head-column injection was performed in 0.25 mM HCOOH water solution (3s, 3.45 kPa). Sample was introduced into the capillary by electrokinetic injection (70 s, 5 kV) followed by short BGE plug (3s, 3.45 kPa). Seven psychiatric drugs (olanzapine, prochlorperazine dimaleate, trifluoperazine dihydrochloride, perphenazine, promazine hydrochloride, clomipramine hydrochloride, and chlorprothixene hydrochloride) were separated in about 6 min. The elaborated method was additionally supported with dispersive liquid-liquid microextraction (DLLME) technique which in summary with FASI provided about 8000-13,000-fold sensitivity enhancement in comparison to the capillary zone electrophoresis (CZE) method with standard hydrodynamic injection (5s, 3.45 kPa).