Determination of bromide and potassium in saline groundwaters by capillary electrophoresis without prior dilution

Two capillary electrophoretic analysis methods are presented; one optimized for the analysis of Br⁻ and the other for determination of K⁺ in groundwaters of high conductivity. The water sampling was performed from the planned final disposal facility area for spent nuclear fuel at Olkiluoto in the municipality of Eurajoki, Finland. Bromide was analysed in an acidic electrolyte solution containing 5 mM formic acid and 42 mM NaCl (pH 3.5) and using direct UV detection (200 nm). Sample stacking was needed for the preconcentration. Potassium was analysed at pH 4.5 using imidazole-18-crown-6 ether solution. The accuracies of the Br⁻ and K⁺ methods were tested using laboratory-made reference sample mixtures with high salt concentration. In the Br⁻ analyses, the limits of detection and determination were 0.1 and 1 mg L⁻¹, respectively. The developed CE analysis for K⁺ in saline water was repeatable (RSD% 14.5–18.0) and the detection and the determination limits were 0.5 and 2.0 mg L⁻¹, respectively. The interlaboratory results showed that CE measurements of Br⁻ and K⁺ were compatible with those made with traditional solvent chemistry techniques.