Separation of catecholamines and their metabolites by adsorption, ion-pair and soap chromatography

The separation of catecholamines and their metabolites has been carried out by high-performance liquid chromatography using three systems: liquid-solid adsorption, ion-pair partition, and soap chromatography. In the last newly developed technique a reversed-phase packing is used in conjunction with an aqueous organic eluent containing a detergent. The detergent is chosen so that its ion can form ion-pairs with ions of the solutes. Soap chromatography proved the best technique in terms of column efficiency (giving 3000-5000 plates in 125 mm), resolution and sensitivity of detection. Noradrenaline, adrenaline and dopamine, their 3-O-methyl derivatives, L-3,4-dihydroxyphenylalanine, homovanillic acid and other related compounds could be separated in less than 10 min at the 10-50-ng level on columns whose plate heights were in the range of 20-40 mum. The dependence of retention on the concentration of organic modifier and on detergent concentration for three anionic detergents is reported. The method is applied to the direct analysis of urine and the potential of the method for such analyses, especially of pathological urines is demonstrated. Soap chromatography is likely to enlarge the scope of application of high-performance liquid chromatography to biochemical analysis. It is a powerful method for the separation of ionizable compounds which could replace conventional ion-exchange chromatography.