The effect of water on separations in non-aqueous capillary electrophoresis systems

Summary Water, in concentrations up to 10%, has been added to organic solvents (dimethylsulphoxide,N-methylformamide, acetonitrile and methanol) used as the buffer solvents in electrophoresis media for non-aqueous capillary electrophoresis. Anionic and cationic test substances have been used to study the effect on separation selectivity and efficiency. The effect on the electroosmotic flow has also been studied. Water added in concentrations up to 0.5% had only a minor effect on the separation selectivity, efficiency or electroosmotic flow in the systems studied. These results indicate that small variations in the water-content of organic solvents are of only minor importance to the reproducibility of non-aqueous capillary electrophoresis systems. The reproducibility of selectivity might, however, be slightly improved by adding 0.1–0.5% water, because true non-aqueous solvents are likely to cause problems as a result of the variable absorption of water.