A STUDY OF A PERMANENTLY COATED POLYMERIC COLUMN FOR SIMULTANEOUS SEPARATION OF INORGANIC ANIONS AND MONO-CARBOXYLIC ACIDS

A polymeric PRP-I reversed-phase column was modified by coating it wit h hexadecyltrimethylammonium bromide and has been used as an analytica l column for the separation of inorganic anions and mono-carboxylic ac ids. An aqueous solution of sodium salicylate was used as the mobile p hase and the detection was performed by indirect UV detection. The exc hange capacity of the permanently coated column was controlled by chan ging the concentration of the organic modifier, acetonitrile, in the c oating solution. The coated column with a low ion-exchange capacity ha s a dual retention mechanism of ion-exchange and surface adsorption fo r carboxylic acids. The contribution of the two mechanisms in the sepa ration was qualitatively evaluated under three chromatographic conditi ons, by means of equations for ion-exchange chromatography, an adsorpt ion model of the electrical double layer and the separation factor. Th e extra-column factors that influence the retention of the surface ads orption of the carboxylic acids were discussed. Among the factors stud ied, the pH of the mobile phase plays a double role, i.e. adjusting th e eluting strength and governing the contribution of each mechanism to the separation. Under the chromatographic conditions selected, simult aneous separation of inorganic anions and mono-carboxylic acids was ac hieved.