A 40-year-old man complains of a sharp general weakness, pain in muscles and joints, fever up to 38.6? C. Painful subcutaneous nodules up to 1 cm in size are palpated on the inner surface of the forearm . In the blood: moderate anemia, elevated ESR, leukocytosis, moderate proteinuria in the urine, microhematuria. To confirm the diagnosis, the patient was prescribed a proteinogram of serum proteins. What method can be used to separate proteins?