School of Stomatology, Tongji University, 200072 Shanghai, China.
Anal Chem. 2010 Aug 15;82(16):6764-9. doi: 10.1021/ac100214p.
The stable carbon isotope compositions of 2-methyltetrols, biomarker compounds for secondary organic aerosols formed from isoprene in the atmosphere, have been determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). In this work, isoprene with various delta(13)C values was used to produce 2-methyltetrols via an oxidation reaction with hydrogen peroxide in sulfuric acid under direct sunlight. The target compounds with different stable carbon isotope compositions were then derivatized by methylboronic acid with a known delta(13)C value and measured by GC/C/IRMS. With delta(13)C values of 2-methyltetrols and methylboronic acid predetermined, isotopic fractionation is evaluated for the derivatization process. Through reduplicate delta(13)C measurements, the carbon isotope analysis achieved excellent reproducibility and high accuracy with an average error of <0.3 per thousand. The differences between the predicted and measured delta(13)C values range from -0.10 to 0.29 per thousand, indicating that the derivatization process does not introduce isotopic fractionation. The delta(13)C values of 2-methyltetrols could be calculated on the basis of the stoichiometric mass balance equation among 2-methyltetrols, methylboronic acid, and methylboronate derivatives. Preliminary tests of 2-methyltetrols in PM(2.5) aerosols at two forested sites were conducted and revealed significant differences in their isotope compositions, implying possible application of the method in helping us understand the primary emission, photochemical reaction, or removal processes of isoprene in the atmosphere.
采用气相色谱/燃烧/同位素比质谱联用仪（GC/C/IRMS），通过化学反应将异戊二烯在大气中氧化生成的二次有机气溶胶的示踪化合物 2-甲基四醇的稳定碳同位素组成进行了测定。在这项工作中，使用具有不同 δ^13^C 值的异戊二烯，在阳光下通过硫酸中的过氧化氢氧化反应生成 2-甲基四醇。然后，将具有不同稳定碳同位素组成的目标化合物与具有已知 δ^13^C 值的甲基硼酸进行衍生化，并通过 GC/C/IRMS 进行测量。通过对 2-甲基四醇和甲基硼酸的 δ^13^C 值进行预测定，评估了衍生化过程中的同位素分馏。通过重复 δ^13^C 测量，碳同位素分析实现了出色的重现性和高精度，平均误差小于 0.3‰。预测和测量的 δ^13^C 值之间的差异在-0.10 至 0.29‰之间，表明衍生化过程不会引入同位素分馏。可以根据 2-甲基四醇、甲基硼酸和甲基硼酸酯衍生物之间的化学计量质量平衡方程来计算 2-甲基四醇的 δ^13^C 值。在两个森林地区的 PM（2.5）气溶胶中对 2-甲基四醇进行了初步测试，结果表明其同位素组成存在显著差异，这意味着该方法可能有助于我们理解大气中异戊二烯的原始排放、光化学反应或去除过程。
