质谱法分析单烷基苯分子量分布

Determination of Molecular Weight Distribution of Monoalkylbenzenes by Mass Spectrometry

前言工业烷基苯是一种组成比较复杂的混合物,已有人采用质谱和色谱/质谱联用技术对其进行了许多研究.Boyer等利用单烷基苯在质谱技术中形成裂片的氢重排规律来测定分子量分布,并已列入ASTM. 在电子轰击下,直链单烷基苯的裂片特征是β-键断裂,产生相当强的CnH2n-7,离子,同时通过氢转移形成CnH2n-6准分子离子。

An analytical method based on Boyer's principle has been developed to determine the molecular weight distribution of monoalkylbenzenes. The correction factor(k)of pseudo molecular ions and the sensitivity coefficient(I_f) have been studied with authetic alkylbenzenes. Experiments show that the value of k is composed of the rearrangement constant(C)and the heavy isotopic contribution k_(io), and the value of I_f increases proportionally with the molecular weight. Mixtures of either straight or branched chain monoalkylbenzenes of C_(12)—C_(31) have been analyzed. The standard deviation is found to be less than 0.5％,and the absolute error less than 1.0％. The relative error of the number average molecular weight calculated from the results is less than 5.0％,comparing with that measured by Vapor Pressure Osmometer(V P O). The method is not suitable for the analysis of mixture of highly branched and straight chain alkylbenzenes which gives much larger deviation.