Application of chemical ionization mass spectrometry to the quantitative analysis of metabolites in biological fluids

Chemical ionization mass spectrometry has been used for the rapid and quantitative analysis of amino acids, fatty acid, free and bound cholesterol and estriol in biological fluids. The analysis depends on the extraction of a particular class of metabolites from the sample with an organic solvent followed by direct chemical ionization mass spectrometry on the extract without prior chromatographic separation. Quantitation has been achieved by the addition of stable isotopically labelled internal standards and mass spectral peak height measurement of the labelled and unlabelled protonated molecular ions. The method permits the determination of metabolites of interest down to a level of 25 ng, whilst still maintaining a signal/noise ratio better than 10:1. The analysis is reproducible with a standard deviation of less than 5%.