Electrophoretic separation of acidic and basic proteins in the presence of micromolar concentrations of an ionic liquid

We report on the use of an ionic-liquid (IL) as additive to an acidic background electrolyte (BGE) for capillary electrophoretic separation of the proteins human serum albumin, transferrin, trypsin inhibitor, hemoglobin, catalase, myoglobin and lysozyme. The method was carried out in a capillary zone electrophoresis mode because the concentration of the ionic liquid is far below its critical micelle concentration, and the proteins were detected by measurement of capacitively coupled contactless conductivity. The addition of the IL to the BGE in micromolar concentration improves (a) the detection sensitivity of the method, (b) the recovery of the protein due to the alleviated wall-adsorption of proteins, and (c) the resolution due to strong interaction between IL and protein. In fact, even microheterogeneous variants of trypsin inhibitor, hemoglobin and catalase could be resolved. Proteins were separated within typically 18 min at pH 2.5, with detection limits of 0.7 to 9.4 mu g mL(-1) (34.8-141.1 nM). The method was specifically employed to analyze human serum samples.