ABSTRACT

Liquid chromatography has been widely employed in multidimensional separations. The penalty of on-line multidimensional high-performance liquid chromatography is that more thought must be given to design of experiments and instrumentation to develop a successful application, compared to the design of successful off-line approaches. The very different selectivities of the various modes of liquid chromatography permit relatively complex mixtures to be analyzed with minimal sample preparation. The simplest approach to valve switching in multidimensional chromatography is to assume that the separation on the first column is sufficiently reproducible that the analyte will always elute from that column within a fixed time window. Amitryptiline and its metabolites, nortriptyline, 10-hydroxynor-tryptiline and 10-hydroxyaminotryptiline were determined in plasma using a coupled system consisting of a reversed phase concentrating column and a cyanopropyl bonded column. The challenges in applying the technique are in efficiently coupling the columns for transfer of analytes and maintaining mobile phase/column compatibility.