A novel liquid chromatographic--electrospray ionisation mass spectrometric (LC--ESI-MS) method has been developed for the determination of escitalopram, an antidepressant in human plasma using paroxetine as internal standard. The method involved liquid--liquid extraction of the analyte from human plasma with a mixture of diethyl ether and dichloromethane (70:30, v/v). The chromatographic separation was achieved within 7.0 min by using 2.0 mM ammonium acetate (pH 5.0)--acetonitrile (54:46, v/v) as mobile phase and a ODS YMCAQ 150 mm x 4.6 mm analytical column; the flow-rate was 1.0 ml/min. Ion signals m/z 325.0 and 330.0 for escitalopram and internal standard, were measured in the positive mode. A detailed validation of the method was performed as per USFDA guidelines and the standard curves were found to be linear in the range of 1.0-200 ng/ml with a mean correlation coefficient more than 0.99. The absolute recovery was more than 75% for both escitalopram and internal standard. The method was simple, sensitive, precise, accurate and was successfully applied to the bioequivalence study of escitalopram in healthy, male, human subjects.

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