On‐line pretreatment using methylcellulose‐immobilized cation‐exchange restricted access media for direct liquid chromatography/mass spectrometric determination of basic drugs in plasma

A novel methylcellulose-immobilized restricted access media column with strong cation-exchange groups on an internal surface (MC-SCX) was evaluated for the direct injection analysis of basic polar drugs in plasma by column-switching liquid chromatography/mass spectrometry (LC/MS). Analytical conditions, including an automated pretreatment step and MS detection, were optimized for a series of basic drugs (doxepin, desipramine, imipramine, nortriptyline, amitriptyline, clomipramine). On-line pretreatment with the MC-SCX column followed by fast gradient analysis using a C18 column resulted in a total analysis cycle time of 7 min for each spiked plasma sample. More than 150 plasma samples spiked with target compounds were measured without compromising MS detection (relative standard deviations less than 11% for all compounds, and regression coefficients greater than 0.99).