A potentiometric study of lithium complexation with catecholamines

A potentiometric study of lithium complexation with tyramine, dopamine, norepinephrine, and 5-hydroxytryptamine was undertaken using monovalent cationic selective and pH glass electrodes. The conditional stability constants for the lithium catecholamine complexes were calculated for a range of pH values from direct potentiometric measurement of the free lithium ion concentration. The ionic strength was maintained at 0.5 with tetramethylammonium chloride and glycine buffers. Temperature was maintained at 25 degrees C. Titration data for the catecholamines and lithium-catecholamine complexes at the same temperature and ionic strength were also obtained using tetramethylammonium hydroxide as titrant. All solutions were maintained essentially oxygen free during the analytical procedure. Alkali metals are generally recognized as being weakly complexed in aqueous solution. The magnitude of the stability constants determined in this study indicates there is a weak interaction of lithium with catecholamines.