Abstract

An experimental study has been executed into the applicability of commercial coated capillaries for the determination of fluoride, formate, chloride, nitrate, sulphate, phosphate and bromide in (natural) aqueous solutions using capillary zone electrophoresis. The life duration of the surface-modified capillaries varied from one measurement until several months depending on the type of capillary. For the modified and common silica capillaries a PMA/TRIS and PMA/TEA/HMOH running electrolyte solution were used respectively. From a set of eight coated capillaries, the amine coated one gave the shortest and most stable migration time for nitrate followed by the C18/BRIJ modified capillary. The influence of the pH of the running electrolyte on the stability of the migration time decreases in order amine<C18/BRIJ coated<silica. Using a set of natural surface water samples, comparable standard deviations in migration time for chloride, nitrate and sulphate are found for the three different capillaries using hydrodynamic injection. Surprisingly, the migration time increased with increasing conductance of the sample solution with this injection mode, probably due to isotachophoretic effects at the initial part of the separation procedure. Finally, recoveries of additions to surface water samples obtained by electrokinetic injection were dependent on the sample itself as well as the component under investigation. For a proper application of this procedure, the use of internal standards is necessary.