New nonextractive and highly sensitive high-performance liquid chromatographic method for determination of paroxetine in plasma after offline precolumn derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole.

New nonextractive and simple offline precolumn derivatization procedures have been proposed, for the first time, for the trace determination of paroxetine (PXT) in human plasma by HPLC with fluorescence detection. Trimetazidine (TMZ) was used as an internal standard. Plasma samples were treated with acetonitrile for protein precipitation and then derivatized with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole in borate buffer of pH 8 at 70 degrees C for 30 min. Separations of the derivatized PXT and TMZ were performed on a Nucleosil CN column using a mobile phase consisting of acetonitrile-10 mM sodium acetate buffer (pH 3.5)-methanol (47 + 47 + 6, v/v) at a flow rate of 1.0 mL/min. The derivatized samples were excited at 470 nm and monitored at an emission wavelength of 530 nm. Under the optimum chromatographic conditions, a linear relationship with good correlation coefficient (r = 0.9998, n = 7) was found between the peak area ratio and PXT concentrations in the range of 5-600 ng/mL. The LOD and LOQ were 1.37 and 4.14 ng/mL, respectively. The intraday and interassay precisions were satisfactory; the RSD did not exceed 4.2%. The accuracy of the method was proved by recovery of PXT from spiked human plasma at levels of 97.28-104.38 +/- 0.41-3.62%. The proposed method had high throughput, as the analysis involved a simple sample pretreatment procedure and short run time (< 10 min). The results demonstrated that the method would have a great value when it is applied in the therapeutic monitoring of PXT.