New preconditioning strategy for the determination of inorganic anions with capillary zone electrophoresis using indirect UV detection

It is widely accepted that preconditioning procedures are indispensable in capillary electrophoresis in order to achieve reproducibility of migration times and peak areas. Several preconditioning strategies have been employed for electrophoretic determinations of inorganic anions using indirect UV d etection including simple flushing with buffer or alkaline or acid pre-rins ing followed by flushing with electrolyte. We investigated the influence of various preconditioning strategies on the reproducibility of migration tim es and peak areas of inorganic anions. The electrolyte systems for indirect UV detection were based on pyromellitic acid and chromic acid respectively as UV absorbing probes and hexamethonium hydroxide as electroosmatic flow modifier. Preconditioning agents under investigation were electrolyte buffe r, NaOH, HCl and the free acids of the UV absorbing probes. Investigations showed that reproducibility of migration times and peak areas can be signif icantly improved by acid pre-rinsing using the corresponding acid of the UV absorbing probes compared to preconditioning by flushing the capillary wit h buffer. In contrast to acid pre-rinsing using hydrochloric acid no interf ering signals within the migration time window of inorganic anions under in vestigation can be observed. The optimized preconditioning procedure yields relative standard deviations of migration times less than 0.25% (n = 10). Relative standard deviations of corrected peak areas were below 5% applying acid preconditioning using pyromellitic acid. (C) 2000 Elsevier Science B. V. All rights reserved.