DETERMINATION OF POLYCARBOXYLIC ACIDS BY CAPILLARY ELECTROPHORESIS WITH COPPER COMPLEXATION

Reversed-polarity CE on unmodified silica, making use of copper sulfate as a combination complexation agent/electrolyte and myristyltrimetylammonium bromide as an electroosmotic flow modifier, has been shown to be a reliable and rapid method of analysis for polycarboxylic acid builders. Since separation is governed by a combination of charge and charge density, a number of similar polycarboxylic acids can be identified by unique retention times. Baseline resolution and symmetrical peak shapes are observed for a mixture of polycarboxylic acids including oxydisuccinic, ethylenediaminetetraacetic, nitrilotriacetic and diethylenetriaminepentaacetic acids, Using direct detection at 254 nm, the limit of detection for these acids approaches 100 ppb (ng/ml), making the technique viable for trace analysis. CE results for nitrilotriacetic and citric acids in formulated products are comparable to results obtained by LC-UV detection. The CE method has been shown, to be as sensitive as LC with amperometric detection, but less selective and easier to stabilize. Other compounds which complex with copper(II) salts, such as ethylhydroxydiphosphonate can be determined at low levels in formulated products using this method.