The unapproved adding of psychiatric drugs, for example phenothiazines, to animal feed and food increases the risk of human organ lesion. Phenothiazines are usually weak natural fluorescent and can be oxidized into strongly fluorescent compounds. In this study, a novel sensitive and convenient post-column on-line oxidizing with lead dioxide solid-phase reactor and HPLC-fluorescence detection method was proposed for simultaneous determination of three banned psychotropic drugs, promethazine, chlorpromazine and thioridazine. Three compounds were successfully separated on an Agilent TC-C18 column (250 mm×4.6 mm, 5 μM, USA) with the mobile phase of water (A) and acetonitrile (B) (both containing 0.5% (v/v) formic acid). A gradient elution was programmed as follows: 0–3 min, maintaining 38% (v/v) A; 3-15 min, 38–45% A; 15–30 min, 45–38% A, pumped at a flow rate of 1.0 mL min-1. Fluorimetric detection was performed at λex/λem of 332 /373 nm for promethazine, 340/380 nm for chlorpromazine and 352/432 nm for thioridazine. The results showed a good linearity with a correlation coefficient (r ≥0.995) over the range of 30.0-4976.4 μg L-1 for promethazine, 2.0-2153.2 μg L-1 for chlorpromazine, and 15.0-3088.0 μg L-1 for thioridazine. The limit of detection (LOD, S/N=3) was 9.8 μg L-1 for promethazine, 0.6 μg L-1 for chlorpromazine and and 4.9 μg L-1 for thioridazine, respectively. The method was successfully applied to the analysis of phenothiazines in pig feed and tissue, and the average spiked recoveries were in the range of 69.1-115.4%.

Acknowledgments The project was supported by National Natural Science Foundation of China (No. 21275098) and Doctor Base Foundation of Chinese Ministry of Education (No. 20110202110005).