Simultaneous determination of magnesium and potassium in lymphocytes, erythrocytes and thrombocytes

A standardized method for the determination of magnesium and potassium in the lymphocytes, erythrocytes, and thrombocytes of normal subjects is described. The procedure consists of four steps: 1) the removal of platelets from the remaining cells and heparin plasma, 2) the isolation of platelet-poor lymphocytes by means of density-gradient centrifugation of the buffy-coat, 3) the purification of blood cells by repeated washings, and 4) the determination in cell lysates of magnesium by atomic absorption spectrometry and of potassium by flame photometry. In order to get reproducible lymphocyte magnesium values, it was necessary to obtain a mean lymphocyte recovery of 60% with a purity of 97% (nucleated cells), this yield containing less than 5 thrombocytes per lymphocyte and less than 4 erythrocytes per 100 lymphocytes. Under these conditions, the normal content of magnesium in lymphocytes was 3.5-5.7 fmoll/cell (n = 18), that of potassium was 38.8-63.5 fmol/cell. The precision (CV) of the whole procedure measured with 10 identical samples from each of 5 persons was 5.7% for lymphocyte magnesium and 7.8% for potassium, respectively. The concentration of magnesium in erythrocytes was 1.99-2.43 mmol/l and that of potassium was 85.8-102.5 mmol/l. The precision was 3.6% for magnesium and 2.2% for potassium. The content of magnesium in thrombocytes was found to be 0.07-0.12 fmol/cell.