Field-ionization relative sensitivities for the analysis of saturated hydrocarbons from fossil-energy-related materials

Abstract

Field-ionization relative sensitivities relative to decane have been determined at ion-source temperatures of 270–300°C for 19 n-alkanes and cycloalkanes. The relative sensitivities are independent of sample composition within the limits of experimental precision. The n-alkane relative mole sensitivities increase by ca. 0.10 per carbon atom. Thus, the n-alkane relative gram sensitivities are unity within experimental precision. The variation in the n-alkane relative gram sensitivities at low ion-source temperatures reflects an increase in the relative mole sensitivity per carbon atom as the temperature is decreased. This result clearly favors the use of high ion-source temperatures in quantitative analysis. Cycloalkanes field ionize more efficiently on a mole basis than do alkanes having the same carbon number. The relative mole sensitivities for the first members in the cycloalkane series are interpreted in terms of the perturbation on the sensitivity for cyclohexane by naphthenic carbons. In order to predict relative gram sensitivities for saturated hydrocarbons the experimental values are correlated with the dependence of the relative mole sensitivity on the structure of the parent hydrocarbon type and the carbon number of the alkylated homologs.