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首页> 外文期刊>Journal of Atmospheric Chemistry >A technique for atmospheric measurements of stable carbon isotope ratios of isoprene, methacrolein, and methyl vinyl ketone
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A technique for atmospheric measurements of stable carbon isotope ratios of isoprene, methacrolein, and methyl vinyl ketone

机译：大气测量异戊二烯，甲基丙烯醛和甲基乙烯基酮的稳定碳同位素比的技术

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摘要

A technique was developed to measure stable carbon isotope ratios (~(13)C/~(12)C) of light volatile organic compounds (VOCs) such as isoprene, methacrolein (MACR) and methyl vinyl ketone (MVK) using gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). An automated sampling and cryofocussing system allowed for the extraction of VOCs from air samples of up to 140 L of air collected over 3 h, and the subsequent ~(13)C/~(12)C analysis of the VOCs by GCC-IRMS. Chromatography using selective transfer between two columns was used to improve the separation for selected compounds, increasing peak resolution and attaining less noisy baselines. Still, some target compounds could not be completely separated from co-eluting peaks. To reduce the bias of isotope ratio determinations, which can result from incomplete peak resolution, a peak-fitting procedure has been developed. In cases of overlapping peaks or substantial baseline drift, this peak fitting allows more accurate determination of isotope ratios than conventional integration schemes. Comparisons between off-line IRMS measurements and a peak-evaluation procedure using a prepared VOC gas-phase standard show that isotope ratios derived from large (＞1 ng of carbon per peak) and well-resolved peaks have a reproducibility of ±0.3‰. With smaller masses in the range of 0.1-1 ng of carbon, reproducibility decreased to ±(0.5-0.8)‰. For a 140 L sample of air, such small masses of carbon correspond to mixing ratios in the low pptV range. The developed measurement technique was applied to a small set of ambient air samples taken during hot, sunny periods from late May to early August, 2005, at Forschungszentrum Juelich, Germany, a semi-rural area. The range of δ~(13)C values determined for isoprene, benzene, and toluene are consistent with those reported in the literature. GCC-IRMS results of δ~(13)C for ambient samples of isoprene, MACR, and MVK, measured at mixing ratios of 15-280 pptV, are presented and discussed.
机译：开发了一种利用气相色谱燃烧法测量异戊二烯，甲基丙烯醛（MACR）和甲基乙烯基酮（MVK）等轻挥发性有机化合物（VOC）的稳定碳同位素比（〜（13）C /〜（12）C）的技术同位素比质谱法（GCC-IRMS）。一个自动采样和低温聚焦系统允许在3小时内从最多收集到的140 L空气样本中提取VOC，随后通过GCC-IRMS对VOC进行〜（13）C /〜（12）C分析。使用在两根色谱柱之间进行选择性转移的色谱法，可以改善所选化合物的分离效果，提高峰分离度并降低噪声基线。但是，某些目标化合物仍无法与共洗脱峰完全分离。为了减少由于不完全的峰分离而导致的同位素比值测定的偏差，开发了一种峰拟合程序。在峰重叠或基本基线漂移的情况下，与常规积分方案相比，这种峰拟合可更准确地确定同位素比。使用已制备的VOC气相标准液对离线IRMS测量结果和峰评估程序进行的比较表明，从大峰（每个峰＞ 1 ng碳）和分辨良好的峰得出的同位素比具有±0.3‰的重现性。碳质量在0.1-1 ng范围内时，较小的重现性降低至±（0.5-0.8）‰。对于140 L的空气样品，如此小的碳质量对应于低pptV范围内的混合比。这项先进的测量技术已应用于2005年5月下旬至2005年8月上旬在炎热，晴天期间在德国半农村地区Forschungszentrum Juelich采集的一小部分环境空气样本。异戊二烯，苯和甲苯的δ〜（13）C值范围与文献报道一致。给出并讨论了以15-280 pptV的混合比测量的异戊二烯，MACR和MVK环境样品的δ〜（13）C的GCC-IRMS结果。

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