Determination of ammonium and metal ions by capillary electrophoresis–potential gradient detection using ionic liquid as background electrolyte and covalent coating reagent

A capillary zone electrophoresis (CZE)–potential gradient detection (PGD) method coupled with field-amplified sample injection was developed to determine alkali metal, alkaline-earth metal, nickel, lead and ammonium ions. The capillary surface was coated with dialkylimidazolium-based ionic liquid and thus the electroosmotic flow (EOF) of the capillary was reversed. The buffer composed of 7.5 mM lactic acid, 0.6 mM 18-crown-6, 12 mM α-cyclodextrin (α-CD); it was adjusted to pH 4.0 by 1-hexyl-3-methylimidazolium hydroxide. The 11 cations were baseline separated within 14 min with 5.1–18.9·104 plates (for 40-cm-long capillary) in separation efficiency, and the detection limits were in the range of 0.27–7.3 ng/ml. The method showed good reproducibility in terms of migration time with RSD ≤ 0.90% for run-to-run and ≤1.65 for day-to-day assessment.