大气乙醛碳同位素分析方法的研究

摘要

A method was described for determination of carbon isotope composition of acetaldehyde in ambient air together with combined gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Through acetaldehyde via NaHSO3 and cysteamine derivatization, it was found that no carbon isotope fractionation occurred during derivatization reaction process (the differences between measured and calculated acetaldehyde derivatives were 0. Ll‰ to 0.35‰, within precision limits of GC/C/IRMS system). By determining carbon iso-topic compositions of cysteamine and acetaldehyde-cysteamine derivative, δ13C values of acetaldehyde in ambient air could be calculated through a mass balance. Using the method, almost identical δ13C values for acetaldehyde in ambient air were found at the same site [ they were ( -34.21 ±0. 27)‰ and ( -31.23±0.16)‰at two different sampling sites, respectively]. The method could be used as an effective tool to provide valuable information on different sources of acetaldehyde in ambient air.%利用气相色谱/燃烧/同位素比值质谱(GC/C/IRMS)分析技术,采用NaHSO3与半胱胺衍生化方法,测定了气态乙醛在衍生化反应过程中的碳同位素效应,探讨了采用该方法测定大气乙醛碳同位素组成的可行性.试验测定了乙醛、衍生剂半胱胺及相应衍生物的碳同位素比值,结果表明,乙醛衍生物的δ13C测量值与理论值的偏差范围为0.11‰～0.35‰,在仪器精密度范围内(＜0.50‰),即在衍生化过程中基本不会发生碳同位素分馏.采用该方法初步测定了大气中乙醛的碳同位素组成,实测数据显示,广州地化所和肇庆鼎湖山大气乙醛δ13C平均值分别为(-34.21±0.27)‰和(-31.23±0.16)‰,相同采样点的大气乙醛碳同位素组成基本不变,可见该方法可作为研究大气乙醛不同排放源的一种有效方法.