Simultaneous measurement of serotonin and paroxetine in rat brain microdialysate by a single-pump column-switching...

Simultaneous quantitation of paroxetine and serotonin in rat brain microdialysate is presented as a means to study the neuropharmacokinetics and neuropharmacodynamics of paroxetine, a selective serotonin reuptake inhibitor. In order to achieve this objective, a single-pump column-switching technique was developed. Optimization of the mobile phase in terms of the concentration of ion-pairing agent, pH of mobile phase, temperature of the stationary phase and concentration of organic modifier was investigated and a single mobile phase was developed for both separations. The design was such that the switching valve employed column I (50 mm length) and column II (250 mm length) in series in position A. At 15.3 min, the valve was switched to position B, in which the flow of the mobile phase was directed only through the short column (column I). A flow gradient program was used to increase the flow-rate from 0.125 ml/min to 0.4 ml/min, which enabled a reduction in total analysis time to less than 20 min. The limits of detection for serotonin and paroxetine were 6 fmol and 300 fmol, respectively. The accuracy of the method demonstrated percent differences from spiked samples that were within 12.5% and the precision was found to be within 10% R.S.D.