Chiral liquid chromatographic determination of mirtazapine in human plasma using two-phase liquid-phase microextraction for sample preparation

A simple, inexpensive and efficient preconcentration and clean-up liquid-phase microextraction method (LPME) using porous polypropylene hollow fibre membrane was developed for the extraction of the antidepressant mirtazapine from human plasma. The effects of different parameters influencing the efficiency of extraction were described and optimized. Under optimized conditions, mirtazapine was extracted with 22 μl toluene from 0.7 ml of plasma previously diluted with 3.1 ml deionized water and alkalinized with 0.15 ml 10 M NaOH. Mefloquine was used as internal standard. The chromatographic analysis was carried out through chiral liquid chromatography (LC) using a Chiralpak AD column and hexane-ethanol (98:2, v/v) plus 0.1% diethylamine as mobile phase, at a flow rate of 1.5 ml min−1. Detection was carried out at 292 nm. The mean recoveries of (+)-(S)- and (−)-(R)- mirtazapine were 29.1 and 28.8%, respectively. The quantification limit (LOQ) was 6.25 ng ml−1 with linear response over the 6.25-625 ng ml−1 concentration range for both enantiomers. Within-day and between-day assay precision and accuracy were studied at three concentration levels (15, 100 and 500 ng ml−1). For both mirtazapine enantiomers, the coefficients of variation (CV) and deviation from the theoretical values were lower than 15% at all concentration levels. The developed and validated method showed that LPME is a promising technique for sample preparation for the analyses of chiral drugs in biological samples.