Ampholytes with close pK(a) values (i.e., good carrier ampholytes (CAs)) are needed as buffers in pH-biased isoelectric trapping (IET) separations. The syntheses of two families of such good CAs were reported recently. Members of the family of diamino sulfate ampholytes (first series) had pl values in the 5.7 < pl < 9.0 range. Members of the family of quaternary ammonium dicarboxylic acid ampholytes (second series) had pl values in the pl < 4.3 range. To further characterize the diamino sulfate ampholytes, their effective mobilities were measured by indirect UV-absorbance detection capillary electrophoresis in a series of background electrolytes (BGEs) with different pH values. The pKa and limiting ionic mobility values of the C As were obtained by fitting these mobility values, as a function of the pH and the ionic strength of the BGEs, to the theoretical mobility expression. These diamino sulfates complete the list of CAs suitable for IET-separations.