IONIC-STRENGTH AND CHARGE NUMBER CORRECTION FOR MOBILITIES OF MULTIVALENT ORGANIC-ANIONS IN CAPILLARY ELECTROPHORESIS

An empirical expression was derived for the actual mobility, mu, valid in an extended range of ionic strength, I, between 0.001 and 0.1 mol/l, using a three-parameter exponential fit for the ratio of actual and absolute mobilities (mu(0) at I = 0), which consists of two variables: ionic strength of the buffer and charge number, z, of the solute. The charge numbers of the solute anions (21 aromatic sulfonates) ranged between 1 and 6, and the ionic strength was varied in the range mentioned using a sodium acetate buffer. The mobilities were determined at 25.0 degrees C in a coated capillary with suppressed electroosmotic flow. The resulting fitting equation, valid under these conditions, is mu/mu(0) = exp(-0.77 root zI). The difference between measured mobilities and mobilities calculated from a tenfold higher or lower ionic strength, using this equation, is within 5% for all experiments. For multivalent ions, mu values can be derived from mu(0) with comparable accuracy.