Determination of noscapine and its metabolites in plasma by coupled-column liquid chromatography

Noscapine, narcotoline and cotarnine were quantified in deproteinized plasma samples by using a coupled-column liquid chromatographic system. The drug and the metabolites were first separated into two groups on a short polar precolumn (-CN) with an acidic mobile phase, containing a low content of acetonitrile. The metabolites were transferred to a hydrophobic analytical column (C18) and separated with a mobile phase containing a counter ion and a co-ion in an acidic buffer with an high acetonitrile content. Noscapine was transferred to another hydrophobic analytical column (C18) with a mobile phase containing a counter ion in an acidic buffer with an high acetonitrile content. Ultraviolet detection at 310 nm was used for all three compounds. The limits of quantitation were 9 ng/ml for noscapine, 13 ng/ml for cotarnine and 20 ng/ml for narcotoline. The within-day precisions were better than 6% (relative standard deviation), and the absolute recoveries were above 82%.