Capillary electrophoresis for protein analysis: separation of human growth hormone and human insulin molecular forms

The capillary zone electrophoresis (CZE) technique was evaluated for separation and quantification of human growth hormone (hGH), human insulin (hI), and proinsulin. Three different molecular forms of biosynthetic hGH (20K, 22K, 44K), methionyl-hGH, biosynthetic hI, and proinsulin, were studied. The hormones were separated with uncoated capillaries, and various analytical conditions were tested (different buffers, ionic strength, pH). The samples were introduced both at positive pressure and electrokinetically, and the voltage applied was varied in each case. Linearity, repeatibility, and limit of detection (0.8 microM for hGH and 1.3 microM for insulin) were determined. Different purification steps were tried in order to find a suitable preanalytical procedure for hGH and hI purification from plasma. Recovery rates from 65 to 80% were obtained.