Determination of milk proteins by capillary electrophoresis

The determination of milk proteins by capillary zone electrophoresis (CZE) is hampered by the adsorption of the solute on the capillary wall. The effects of pH, ionic strength of the buffer and polymeric additives were studied in combination with a hydrophilically coated capillary. Optimum separations were obtained at low pH (2.5-3) in aqueous solutions containing 6 M urea and methylhydroxyethylcellulose, resulting in a complete separation of the serum proteins and caseins, including some genetic variants. The results were compared with those achieved with reversed-phase HPLC. With CZE, theoretical plate numbers in the range 300,000-700,000 were obtained. The relative standard deviations for migration times were below 0.08% and for peak areas were 2-4%. The separation of cow, goat and sheep milk proteins and of heat-damaged casein is reported.