Joint Research Centre - European Commission, Institute for Reference Materials and Measurements (IRMM), Retiesewg 111, B-2440, Geel, Belgium.
Rapid Commun Mass Spectrom. 2014 Jan 30;28(2):200-8. doi: 10.1002/rcm.6769.
Compound-specific stable isotope analyses of carbon require relatively large amounts of sample for reliable analyses. Commonly applied injections of 1 μL may thus be insufficient for samples with low concentrations of pollutants (e.g. air particulate matter) or when the amount of a sample is limited.
A Large-Volume Injection (LVI) method for carbon stable isotope ratio analysis of Polycyclic Aromatic Hydrocarbons (PAHs) was optimized in this study. Gas chromatography/combustion/isotope ratio mass spectrometry (GCCIRMS) and ion trap mass spectrometry (ITMS) were used for the determination of stable carbon isotope ratios and quantification of compounds, respectively.
The optimized method resulted in very good reproducibility, even for the most volatile PAH, naphthalene, when a small amount of higher boiling co-solvent was used. No significant fractionation of isotope ratios could be seen and the recoveries of analytes were similar to or better than that of a splitless cold injection.
Injection of 100 μL, instead of the commonly used 1 μL, increases the detection limit for PAHs significantly and/or simplifies the sample preparation step. Using our optimized method, stable carbon isotope ratios can be reliably measured in samples with concentrations of PAHs down to 0.05-0.1 ng μL(-1).
碳的化合物特异性稳定同位素分析需要相对大量的样品才能进行可靠的分析。因此，对于浓度较低的污染物（例如空气颗粒物）或样品数量有限的情况，通常应用的 1μL 注射量可能不足。
本研究优化了用于多环芳烃 (PAH) 碳稳定同位素比分析的大体积进样 (LVI) 方法。气相色谱/燃烧/同位素比质谱 (GCCIRMS) 和离子阱质谱 (ITMS) 分别用于稳定碳同位素比的测定和化合物的定量。
即使使用少量高沸点共溶剂，优化后的方法也能使最易挥发的 PAH（萘）具有非常好的重现性。没有观察到同位素比的明显分馏，并且分析物的回收率与不分流冷进样相似或更好。
与通常使用的 1μL 相比，注射 100μL 可显著提高 PAH 的检测限，并且/或者简化样品制备步骤。使用我们优化的方法，可以可靠地测量浓度低至 0.05-0.1ngμL-1 的 PAH 样品中的稳定碳同位素比。
