Salt effects in capillary zone electrophoresis .1. Dependence of electrophoretic mobilities upon the hydrodynamic radius

An examination of the derivation of the equation relating electrophoretic mobility (mu(ep)) to charge and the hydrodynamic radius (r) shows that the 1/r dependence arises from an approximation. A more generalised approach yields a 1/r(2) dependence and includes the known 1/root I dependence as well. Nine totally ionised sulphonamides have been used to test the proposed relationship between mu(ep) and r, and at each of four buffer concentrations utilised the correlations favour 1/r(2). For large molecules, mu(ep) has frequently been demonstrated to be proportional to 1/M-r(2/3), which can be equivalent to 1/r(2). However, it has been suggested that there may be a transition from 1/r dependence for small molecules to a 1/r(2) dependence for large molecules. Hence we have used literature data for a series of twenty-two peptides varying in size between 3 and 39 amino acids long to test that theory and the generality of the 1/r(2) dependence. The calculations indicate a consistent dependence upon 1/r(2). (C) 1997 Elsevier Science B.V.