Optimisation of the separation of anions by ion chromatography-capillary electrophoresis using indirect UV detection

The separation of a complex mixture of inorganic and organic anions by ion chromatography-capillary electrophoresis using a cationic polymer added to the background electrolyte and indirect UV detection has been studied. The addition of unmodified polymer to an electrolyte suitable for indirect dete ction resulted in the appearance of a system peak due to the counter-anion on the polymer and while the position of the analytes relative to this syst em peak could be changed, this was found to be an unacceptable approach for mixtures of large numbers of analytes. Although conversion of the polymer to replace the counter-ion with the indirect W detection probe ion simplifi ed the system, this approach restricted the flexibility of the system becau se the probe and polymer concentration were necessarily linked. This limita tion could be overcome by selecting the appropriate type of probe ion, with probes having a low ion-exchange selectivity coefficient providing greater retention of analytes than probes with a high ion-exchange selectivity coe fficient. Three electrolyte systems with different probes (benzoate, chroma te and phthalate) were modelled using a previously derived migration equati on and this was used to optimise the electrolyte composition to enable the separation of a mixture of 24 inorganic and organic anions within 7 min. Th e electrolyte composition was then optimised for the analysis of anions in Bayer liquor with the-final separation selectivity being substantially impr oved for selected key analytes. (C) 2001 Elsevier Science BN. All rights re served.