TOTAL SERUM-CHOLESTEROL BY ISOTOPE DILUTION-MASS SPECTROMETRY - A CANDIDATE DEFINITIVE METHOD

  • 1 January 1980
    • journal article
    • research article
    • Vol. 26  (7) , 854-860
Abstract
A highly accurate and precise method is described for determination of total cholesterol in [human] serum by isotope dilution/mass spectrometry. The method was developed for use in establishing the accuracy of a candidate reference method for total cholesterol; for a Study Group of the Committee on Standards of the American Association for Clinical Chemistry, it fulfills their criteria for a definitive method. Cholesterol-d7 is added to serum, with the weight ratio of cholesterol-d7 to total serum cholesterol kept near 1:1. The esters are hydrolyzed, and the cholesterol is separated and converted into the trimethylsilyl ether derivative for measurement by combined gas chromatography/mass spectrometry. The intensity ratio of the molecular ions at m/z 465 and 458 is measured for each sample and for 2 calibration mixtures, according to a prescribed bracketing protocol. A weight ratio for the sample is obtained by linear interpolation of the ion-intensity ratios, and the total cholesterol is then calculated. The method was applied 4 times over several wk to each of 5 serum pools. Statistical analysis involving consideration of replication error and variability between wk gave a coefficient of variation for a single measurement of 0.36%. The absence of interferences in the method was demonstrated by measurements at several other masses.