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

A HPLC assay with tandem mass spectrometric detection in the positive-ion a tmospheric pressure chemical ionisation (APCI) mode for the sensitive deter mination 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-mul plasma aliquots, at pH 6.5, allow ed a reliable quantification of retigabine and the acetyl metabolite down t o 1 ng/ml. Injection of 500 mul of diluted plasma onto a C-2 stationary pha se-based column switching system in combination with a 75 mmx4 mm reversed- phase analytical column at a flow-rate of 0.5 ml/min provided cycle times o f 4 min per sample. The standard curves were linear from 1 to 1000 ng/ml us ing weighted linear regression analysis (1/x(2)). The method is accurate (m ean accuracy less than or equal to+/-10%), precise (RSD <+15%) and sensitiv e, providing lower limits of quantification in plasma of 1 ng/ml for retiga bine (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. (C) 2000 Elsevier Science B.V. All rights reserved.