CAPILLARY ELECTROPHORETIC DETERMINATION OF DEGRADATION PRODUCTS OF NITRILOTRIACETIC ACID USED AS A COMPLEXING AGENT IN A DESULFURATION PROCESS

Capillary electrophoresis (CE) was assessed for the determination of t he expected degradation products of nitrilotriacetic acid (NTA), viz., imiodiacetic acid (IDA), dimethyliminoacetic acid (DMIA), N-methylgly cine (NMG), glycine (GLY), acetate, formate and ammonium, in solutions containing iron(III)-NTA complexes which were used for the desulphura tion of industrial gases. Owing to the wide range of absolute mobiliti es and acidic constants of these analytes, the analytical requirements were best met with three different sets of operating conditions, all carried out with indirect absorbance detection. The more mobile ions ( formate, acetate and NTA) were obtained without interference with othe r process-relevant anions using a buffer of pH 6 and an electroosmotic flow modifier under reversed polarity. Using normal polarity and no m odifier, the less anionic species (GLY, NMG, DMIA) were determined at pH 9.5, while the major degradation product, IDA, was best determined at pH 7. Ammonium can be detected in the last two cases. The cumbersom e presence of iron (III) ions was avoided by either precipitation (pot assium hydroxide) or complexation (ethylenediaminetetraacetic acid). S pecial attention was paid to method validation. The analyses were fast (<6 min) and exhibited low relative standard deviations for migration times (<0.1%) and peak areas (<5%). The methods were applied to monit or the process of desulphuration. The results are well correlated with those obtained by ion chromatography (IC), but CE appeared simpler an d more versatile and cost effective.