Determination of olanzapine in human breast milk by high-performance liquid chromatography with electrochemical detection

A reversed-phase high-performance liquid chromatographic-electrochemical as say was developed and validated for the quantification of olanzapine in hum an breast milk. The assay involved a solid-phase extraction (SPE) of olanza pine and its internal standard on a Bond Elut Certify LRC mixed-mode cartri dge. After conditioning of the SPE cartridge, human milk (1 ml) was passed through the cartridge. The cartridge was washed with five separate washing steps to remove endogenous compounds, and the analytes were eluted with eth yl acerate-ammonium hydroxide (98:2, v/v) solution. The eluate was evaporat ed to dryness (gentle stream of nitrogen at 40 degrees C), and the residue was dissolved in mobile phase. The extract was injected onto a YMC basic co lumn (150 mmx4.6 mm I.D., 5 mu m particle size) at a flow-rate of 1 ml/min. A mixture of 75 mM phosphate buffer, pH 7.0-acetonitrile-methanol (48:26.2 6, v/v/v) was used as the mobile phase. Standard curves with a lower limit of quantitation of 0.25 ng/ml of olanzapine were Linear (r(2)greater than o r equal to 0.9992) over a range of 0.25-100 ng/ml. Based on the analysis of quality control (QC) samples, the average inter-day accuracy (RE) was 99.0 % with an average precision (CV) of 6.64% over the entire range. The stabil ity of olanzapine in human milk was established after three freeze-thaw-hea t cycles and storage at -70 degrees C for 10 months. The validated method w as used to measure olanzapine concentrations in human milk during a clinica l trial. (C) 1999 Elsevier Science B.V. All rights reserved.