Total ionization of hydrocarbons from mass spectral data

The total ionization is computed by adding all the mass peaks in the spectrum and multiplying by the sensitivity (current per unit pressure) for the maximum peak. This is divided by the corresponding product for n-butane to obtain a relative value independent of the units used. Data are taken from the API Catalog of Mass Spectral Data using revised values of sensitivity obtained by measuring pressure with a micromanometer. Total ionizations of all the isomers of a compound are nearly equal with only a few values differing greatly from the mean value. This is true in all cases where data are available for many isomers. With some exceptions total ionization increases with increasing number of carbon atoms in each series CnH2n+2, CnH2n, etc. Total ionization tends to decrease in compounds with the same number of carbon atoms and decreasing number of hydrogen atoms but there are many exceptions. Tables summarize data for 198 hydrocarbons. Values of total ionization of isomers will in some cases permit computing all isomers as a group in chemical analysis without identifying the compounds.