Comparison of the concentrations of HDL cholesterol as determined after magnesium-phosphotungstate precipitation or -ultracentrifugation of whole rabbit plasma

and are dissolved with 15 ml of cone. nitric acid on gentle heating. The acid is evaporated to a wet residue. The latter is dissolved into redistilled water. The solution is transferred into a measuring flask of 50 ml and is brought to the volume with water. The pH of the solution thus obtained is approximately 1. A 10-ml aliquot of the obtained solution (containing 0.5 g of selenium) is diluted to 100 ml and, if necessary, the pH is adjusted to 1.5 with dilute nitric acid. The solution is passed through the column with a rate of 0.5 ml/min. Selenium is washed out of the column with 2 ml of 0.01 M HNOa. The trace components are eluted with 6 ml of a 0.05 M solution of DTPA alkalized to pH 10.5 with ammonia. 2-ml portions of the eluate are collected. The column is regenerated with 10 ml of 2 M HNOa and is washed to neutral reaction. The concentration of the trace elements in the eluate is determined by flame, or electrothermal AAS, respectively, depending on the trace level. The calibration curves are prepared in a 0.05 M DTPA solution (pH 10.5).