Simultaneous determination of weakly ionizable analytes in urine and plasma samples by transient pseudo-isotachophoresis in capillary zone electrophoresis

A rapid method for the simultaneous determination of several non-steroidal anti-inflammatory drugs (NSAIDs) in human plasma and urine was developed using transient pseudo-isotachophoresis (ITP) in capillary zone electrophoresis (CZE). The influence of different parameters on resolution and preconcentration efficiency, such as background electrolyte (BGE) composition, sample injection, sample matrix composition, and pH, were studied to optimize the transient pseudo-ITP performance. Optimized conditions were a BGE consisting of 100 mM Na₂B₄O₇ in 10% aqueous MeOH solution and hydrodynamic injection of the sample at 50 mbar for 90 s. The sample was prepared in a solution mixture of 1% NaCl/ethanol (30:70 v/v) at pH 10. Our results show that this simple strategy offers improved sensitivity compared to conventional CZE analysis, reaching a 45-fold preconcentration factor. The detection limits (LODs) were as low as 0.07 mg/L for standard samples with good repeatability (values of relative standard deviation, %RSD < 11%). The method was applied to the analysis of NSAIDs in biological samples. Validation for human plasma and urine samples demonstrated good linearity, low detection limits, and satisfactory repeatability values.