Determination of Trace Impurities in Benzene by GC-CIMS

Abstract

A simple and sensitive method forthe determination of15impurities in benzene by GC-CIMS is presented. One to ten μl of sample is injected into a Finnigan3300EGC-CIMS instrument equipped with a1.5m×2mm i. d. glass column packed with5%squalane(for2-methylpentane, 3-methylpentane and n-hexane)or5m column packed with5%PEG400(for the other12impurities)and the mass fragmentograms of the specific peaks due to QM⁺or(M+29)⁺are recorded. The peaks used are as follows: m/e69for cyclopentane, m/e71for2-methylbutane, m/e77for carbon disulfide, m/e83for methylcgclopentane and cyclohexane, m/e85for2-methylpentane, 3-methylpentane, n-hexane and thiophene, m/e97for methylcyclohexane, m/e93for toluene, m/e135for ethylbenzene and p-, m-, o-xylene. Methane is used both as carrier and reactant gas. Because of high selectivity and sensitivity of the proposed method, satisfactory results were obtained without any preconcentration and the separation of cyclopentane from2-methylpentane and of carbon disulfide from cyclohexane by GC. The determination limit was5-50pg with a precision of about5%. The total impurities in five samples which are all reagent chemicals were found to be0.013-0.28%.