Rapid analysis of aliphatic hydrocarbon impurities in a special grade benzene by gas chromatography and a method of purification of commercial benzene

Abstract

Quantitative determination of a small amount of saturated hydrocarbons in a special grade benzene by gas chromatography has been investigated. Gas chromatograms, were obtained by using a column of tricrecylphosphate or carbowax as a liquid phase and using hydrogen gas as a developing gas. Before the appearance of the peak of benzene, four peaks were obtained. Pure saturated hydrocarbon which was though to be present as an impurity in benzene was added each by each to the pure benzene sample and gas chromatogram for this specimen was obtained in the same way as for the sample benzene. Then qualitative determination of the impurities was made by the comparison to the peak of known substances. In the quantitative determination, a definite amount of ethyl ether was added as an internal standard substance and the relative intensities of the spectra were measured with respect to that of the internal standard. A calibration curve prepared by plotting the relative intensity of the peak of the impurity as the function of its concentration in ether was used for quantitative determination.
As an example of the analysis, the presence of 0.16% n-heptane, 0.08% cyclohexane, 0.07% methylcyclohexane, and a small amount of n-hexane and an unknown impurity was found. By the fractional crystallization, a pure benzene showing no impurity by the above gas chromatography was prepared.