Quantitative determination of isoniazid in biological samples by cation-selective exhaustive injection-sweeping-micellar electrokinetic chromatography

Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis, infects approximately one third of the current world population. Isoniazid is one of the most frequently used first-line anti-TB drugs. In this study, we developed a sensitive cation-selective exhaustive injection–sweeping–micellar electrokinetic chromatography method (CSEI-Sweep-MEKC) for analyzing isoniazid in human plasma. Parameters including acetonitrile (ACN) percentage in the separation buffer; the injection time, and concentration of the high-conductivity buffer; sodium dodecyl sulfate (SDS) concentration; phosphate concentration in the sample matrix; and the sample injection time were all optimized to obtain the best analytical performance. The optimal background electrolyte comprised 50 mM phosphate buffer, 100 mM SDS, and 15% ACN. Non-micelle background electrolyte, containing 75 mM phosphate buffer and 15% ACN, was first injected into the capillary, followed by a short plug of 200 mM phosphate (high-conductivity buffer). Run-to-run repeatability (n = 3) and intermediate precision (n = 3) of peak area ratios were found to be lower than 8.7% and 11.4% RSD, respectively. The accuracy of the method was within 98.1–106.9%. The limit of detection of isoniazod in human plasma was 9 ng mL⁻¹. Compared with conventional MEKC, the enhancement factor of the CSEI-Sweep-MEKC method was 85 in plasma samples. The developed method was successfully used to determine isoniazid concentration in patient plasma. The results demonstrated that CSEI-Sweep-MEKC has the potential to analyze isoniazid in human plasma for therapeutic drug monitoring and clinical research.