Manipulation of Retention of Acids in Ion Exchange Chromatography

Apart from the usual electrostatic effects which govern retention in ion exchange chromatography, one of the main factors affecting retention of carboxylic acids is the molecular adsorption of the acid on the anion exchange resin. The presence of

Figure 6 Analysis of human urine using ion exclusion chromatography. An Interaction ORH-801 column was used with a mobile phase comprising 10mmolL~1 H2SO4 containing 10% methanol. Detection was at 254nm. Solute identities: 1, oxalic acid; 2, oxaloacetic acid; 3, a-ketoisovaleric acid; 4, ascorbic acid and a-keto-^-methyl-n-valeric acid; 5, ^-phenylpyruvic acid; 6, uric acid; 7, a-ketobutyric acid; 8, homoprotocatechuic acid; 9, unknown; 10, unknown; 11, hydroxyphenylacetic acid; 12, p-hydroxyphenyllactic acid; 13, homovanillic acid. (Reprinted with permission from Woo DJ and Benson JR (1984) American Clinical Products Review Jan: 20.)

Figure 6 Analysis of human urine using ion exclusion chromatography. An Interaction ORH-801 column was used with a mobile phase comprising 10mmolL~1 H2SO4 containing 10% methanol. Detection was at 254nm. Solute identities: 1, oxalic acid; 2, oxaloacetic acid; 3, a-ketoisovaleric acid; 4, ascorbic acid and a-keto-^-methyl-n-valeric acid; 5, ^-phenylpyruvic acid; 6, uric acid; 7, a-ketobutyric acid; 8, homoprotocatechuic acid; 9, unknown; 10, unknown; 11, hydroxyphenylacetic acid; 12, p-hydroxyphenyllactic acid; 13, homovanillic acid. (Reprinted with permission from Woo DJ and Benson JR (1984) American Clinical Products Review Jan: 20.)

double bonds in carboxylic acids leads to higher retention factors, probably due to stronger hydropho-bic interactions of the double bond with the polymeric matrix of the resin and also stronger electrostatic interactions between ionic groups. The presence of hydroxy groups in carboxylic acids increases the polarity of the acid and results in stronger interactions both with the aqueous mobile phase (leading to lower retention factors for the acids) and any alkanol substituent of the quaternary ammonium functional group of the anion exchange resin (leading to higher retention factors). Since the adsorption of carboxylic acids plays such an important role in the retention of these acids in ion exchange chromatography, the pKa values of the acids are also important, as are any parameters which influence the dissociation of the acid, such as the pH of the mobile phase and the concentration of any organic solvent. Additionally, the pH of the mobile phase may also affect its elution strength and hence affect retention as well.

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Solar Panel Basics

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