Characterization of buffers for electrokinetic separations

Buffers used in electrophoresis and electrochromatography must have a relatively low ionic strength in order to minimize ohmic heating in the presence of an applied potential. Calculation of pH, ionic strength, and the van Slyke buffer capacity, β, is therefore important. This paper describes thea priori calculation of these parameters for tris buffer made up with either glycine (a zwitterion) or HCl. A quadratic expression for pH, valid over wide ranges, is obtained for both buffer systems. The calculated values of pH, ionic strength, and buffer capacity are shown to agree with experimental results as a function of tris, HCl, and glycine concentrations ranging from 1 to 50 mM. A new parameter, the electrokinetic buffer effectiveness factor, is introduced to characterize buffers being considered for use in electrokinetic systems such as electrochromatography, and is used to determine the appropriate composition ranges for the buffer components.