Analysis Of Basic Drugs By Column-Switching Liquid Chromatography-Mass Spectrometry

Sample throughput in LC/MS analysis is often limited by complex sample preparation methods designed to maximize the selectivity and sensitivity of detection without the constraints of matrix effects. Recent approaches to the acceleration of method development and reduction of analysis times have involved column-switching LC systems in which the first column eliminates macromolecular compounds such as proteins from plasma samples, and is followed by a second column that is used for analytical separations.

Previously, we reported a novel restricted access media (RAM) material, i.e., a methylcellulose- immobilized reversed-phase pretreatment column (MC-ODS), with applications for analysis of drugs in plasma using UV detection and mass spectrometric detection. High recovery, stability and reproducibility were demonstrated after the direct injection of 300 plasma samples totaling 15 mL of plasma.

Although reversed-phase RAM columns are the standard choice for direct injection methods, there are some exceptions. As drugs can be retained on the internal surface by hydrophobic interactions, hydrophilic polar compounds such as cationic drugs or drug metabolites show weak retentive properties, resulting in low recoveries and poor reproducibility. To overcome this problem the MC-SCX column was developed.

The present work describes the analysis of tricyclic antidepressants (doxepin, desipramine, imipramine, nortriptyline, amitriptyline and clomipramine) by LC/MS using the MC-SCX.