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

A reversed-phase high-performance liquid chromatographic-electrochemical assay was developed and validated for the quantification of olanzapine in human breast milk. The assay involved a solid-phase extraction (SPE) of olanzapine and its internal standard on a Bond Elut Certify LRC mixed-mode cartridge. 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 ethyl acetate-ammonium hydroxide (98:2, v/v) solution. The eluate was evaporated 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 column (150 mmx4.6 mm I.D., 5 microm particle size) at a flow-rate of 1 ml/min. A mixture of 75 mM phosphate buffer, pH 7.0-acetonitrile-methanol (48:26:26, 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 (r2> or =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 stability of olanzapine in human milk was established after three freeze-thaw-heat cycles and storage at -70 degrees C for 10 months. The validated method was used to measure olanzapine concentrations in human milk during a clinical trial.