On-line monitoring of kraft pulping liquors with a valveless flow injection–capillary electrophoresis system Original Research Article

A valveless flow injection–capillary electrophoresis system has been developed allowing reproducible injection of samples into an electrolyte stream with the aid of programmable pumps instead of an injection valve. The electrolyte stream transports the injected samples to an interface into which a capillary has been inserted. High voltage is applied throughout the process. On reaching the capillary aperture, a small fraction of the sample plug is electrokinetically introduced. Typical relative standard deviation values in calibration tests were in the range 2–6% for small inorganic anions. The system has been assessed for on-line monitoring of the major anions present in kraft pulping liquors. The preferred electrolyte solution for this application comprised 3.5 mmol l−1 chromate and 30 μmol l−1 cetyltrimethylammonium bromide at pH 11. Samples were taken every 6 min, fully automatically. The system also allows rates of oxidation to be monitored in terms of changes in the concentrations of sulphite, sulphide and thiosulphate ions, as demonstrated by inducing and following accelerated oxidation in a test sample.