Determination of retigabine and its acetyl metabolite in biological matrices by on-line solid-phase extraction (column switching) liquid chromatography with tandem mass spectrometry

Abstract

A HPLC assay with tandem mass spectrometric detection in the positive-ion atmospheric pressure chemical ionisation (APCI) mode for the sensitive determination of retigabine [( I), D-23129] and its acetyl metabolite [( II), ADW 21-360] in plasma was developed, utilising the structural analogue (D-10328), ( III), as internal standard. Automated on-line solid-phase extraction of diluted plasma samples, based on 200-μl plasma aliquots, at pH 6.5, allowed a reliable quantification of retigabine and the acetyl metabolite down to 1 ng/ml. Injection of 500 μl of diluted plasma onto a C 2 stationary phase-based column switching system in combination with a 75 mm×4 mm reversed-phase analytical column at a flow-rate of 0.5 ml/min provided cycle times of 4 min per sample. The standard curves were linear from 1 to 1000 ng/ml using weighted linear regression analysis (1/ x 2). The method is accurate (mean accuracy ≤±10%), precise (RSD <±15%) and sensitive, providing lower limits of quantification in plasma of 1 ng/ml for retigabine ( I), and 2.5 ng/ml for the metabolite ( II) with limits of detection of 0.5 ng/ml for both analytes. Up to 200 unknowns may be analysed each 24 h per analyst.