Determination of Trace Impurities in N-Hexane and N-Heptane by GC/CIMS

A simple and sensitive method for the determination of thirteen impurities in n-hexane or n-heptane by GC/CIMS is presented. One to three μl of sample is injected into a Finnigan 3300E GC/CIMS instrument equipped with a 5 m × 2 mm i.d. glass column packed with 5% squalane/Uniport K (80~100 mesh), and the mass fragmentograms of the specific peaks due to QM+ are recorded. The peaks used are as follows: m/z 69 for cyclopentane, 71 for 2-methylbutane and n-pentane, 79 for benzene, 83 for methylcyclo-pentane and cyclohexane, 85 for 2-methylpentane, 3-methylpentane and n-hexane, 93 for toluene, 97 for methylcyclohexane, 99 for 2-methylhexane, 3-methylhexane and n-heptane. Methane is used both as carrier and reactant gas. Owing to high selectivity and sensitivity of the proposed method, satisfactory results were obtained without the complete GC separation. The determination limit was 10~200 pg with a precision of about 5%. The total impurities in n-hexane or n-heptane samples which are all reagent chemicals were found to be 0.11~2.9%.