PREDICTION OF ELECTROPHORETIC MOBILITIES - 1 - MONOAMINES

The mobility of an ion is of fundamental importance in capillary elect rophoresis, The size, shape, and other physicochemical parameters of m onoamines are determined using molecular modeling, These parameters ar e used to generate regression expressions to predict absolute (infinit e dilution) mobilities, Molecular volume or mass is the strongest dete rminant of electrophoretic mobility, However, molecular volumes calcul ated via molecular modeling varied systematically depending on the sof tware used, and so molecular mass is the favored descriptor, Neither t he classical spherical (Huckel) nor ellipsoidal (Perrin) models were r easonable predictors of mobility, In accord with empirical expressions , such as the Wilke-Chang equation for diffusion, the absolute mobilit ies correlate with mass (or volume) to a much greater power than predi cted by Stokes's law. Incorporation of the effects of hydration using the McGowan waters of hydration increments further improved the predic tions, The best equation for predicting absolute mobilities of monoami nes is mu(0) = [(5.55 +/- 0.73) x 10(-3)]/[W(0.579 +/- 0.026) + (0.171 +/- 0.054)H] where W is the molecular weight and H is the mean waters of hydration calculated using the McGowan increments, The uncertainti es are the standard deviations of the parameters, This equation yielde d an average prediction error of 4.1% for the data set used to generat e the expression (literature absolute mobilities for 34 monoamines pos sessing no other functional groups), 7.2% for an independent data set from the literature (absolute mobilities for seven monoamines possessi ng other functional groups), and 3.3% for an experimentally determined data set (13 monoamines determined using capillary electrophoresis).