Ion subtraction — a computer-aided step in the geochemical analysis of fossil fuels

The subtraction of the signal intensities of the ion fragments m/e 149 and m/e 151 in the GLC-MS computer analysis of the saturated hydrocarbons of a fossil fuel, reveals the distribution of the 5α and 5β steranes. This technique is a convenient method of establishing the efficacity of the thiourea clathration step, and simplifies routine geochemical analysis. Subtraction of the signal intensities of the ion fragments m/e 218 and m/e 217 reveals the distribution of 14α and 14β sterane isomers, and is a further refinement in the study of geological steroids.