准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质...准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质谱,结合高选择性的铵根离子加成模式,发展了铵根-电离质谱法(ammonium chemical ionization mass spectrometry,NH_(4)^(+)-CIMS),成功实现了对不同种类的RO_(2)自由基以及含氧VOCs物种的高灵敏度检测.通过自主搭建的标定系统,实现了基于质谱法测量RO_(2)自由基的直接标定,有效降低了由于灵敏度替代造成的测量不确定性.该套系统首先应用于近实际大气条件下α-蒎烯臭氧氧化体系的研究,共检测到13种一代反应产物,包括5种RO_(2)自由基和8种闭壳物种,其中来自OH氧化反应生成的过氧自由基C_(10)H_(17)O_(3)占比最大,臭氧氧化α-蒎烯生成的过氧自由基C_(10)H_(15)O_(4)发生多步自氧化及双分子反应,生成含更高氧数的过氧自由基和闭壳产物,证实了α-蒎烯自氧化反应通道的重要性.现有大气化学机理可基本捕捉α-蒎烯臭氧化反应的产物分布,但不同氧化通道产物的相对占比受模型设置的反应速率和反应通道分支比影响存在较大不确定性.此外,氢摘取通道可能对OH自由基氧化α-蒎烯具有重要贡献,但机制待进一步探索.本研究展示的NH_(4)^(+)化学电离质谱技术,具有高灵敏度、高分辨率、低检测限等优点,特别是对中等氧化程度的闭壳产物和RO_(2)自由基的检测.未来,这套系统有望在更复杂的大气环境中揭示VOCs的演化规律和降解机制,为大气环境保护提供重要科学依据.展开更多
Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions...Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions with different concentrations（0.1%,0.5%,1.0%,3.5% and 5.0% in mass fraction） was evaluated by electrochemical measurements and immersion tests.The results showed that the corrosion rate of the MAO coated AZ91D increased with increasing chloride ion concentration.The main form of corrosion failure was localized corrosion for the MAO coated AZ91D immersed in higher concentration NaCl solutions（1.0%,3.5% and 5.0%）,while it was general corrosion in dilute NaCl solutions（0.1% and 0.5%）.Two different stages of the failure process of the MAO coated AZ91D could be identified：1） occurrence of the metastable pits and 2） growth of the pits.Different equivalent circuits were also proposed based on the results of electrochemical impedance spectroscopy（EIS） for the MAO coated AZ91D immersed in different concentrations of NaCl solutions for 120 h.展开更多
Several recently developed analytical techniques, based on high-end mass spectrometry and chromatography, for dealing with challenges in petroleum characterization are reported. Folded flight path time-of-flight mass ...Several recently developed analytical techniques, based on high-end mass spectrometry and chromatography, for dealing with challenges in petroleum characterization are reported. Folded flight path time-of-flight mass spectrometry provides resolving power up to 100000, enabling accurate mass measurement for molecular formula determination with high confidence. Atmos- pheric pressure chemical ionization （APCI） can be used in both gas chromatography （GC, as APGC） and liquid chromatog- raphy （LC） for analyzing non-polar hydrocarbons as well as polar compounds. The improvement in chromatography facilitates the mass spectrometric analysis through online coupling. Comprehensive two-dimensional gas chromatography （GCxGC） re- solves overlapping components, rendering accurate identification and quantitation. Supercritical fluid extraction has been de- veloped as an alternative method to replace traditional solvent extraction methods and eliminate the use of large volumes of solvents that can be harmful to health and environment. Supercritical fluid chromatography （SFC） has been developed as a convergence of GC and LC chromatographic techniques. The use of SFC for heavy oils and residua has been demonstrated. Prospective developments in the use of mass spectrometric and chromatographic methods for petroleum characterization are also described.展开更多
文摘准确识别和定量挥发性有机化合物(volatile organic compounds,VOCs)氧化中间产物(包括闭壳产物和有机过氧自由基RO_(2)),对于厘清其降解机理和实现二次物种精准模拟与精细化管控十分关键.本研究基于最新开发的质子转移反应-飞行时间质谱,结合高选择性的铵根离子加成模式,发展了铵根-电离质谱法(ammonium chemical ionization mass spectrometry,NH_(4)^(+)-CIMS),成功实现了对不同种类的RO_(2)自由基以及含氧VOCs物种的高灵敏度检测.通过自主搭建的标定系统,实现了基于质谱法测量RO_(2)自由基的直接标定,有效降低了由于灵敏度替代造成的测量不确定性.该套系统首先应用于近实际大气条件下α-蒎烯臭氧氧化体系的研究,共检测到13种一代反应产物,包括5种RO_(2)自由基和8种闭壳物种,其中来自OH氧化反应生成的过氧自由基C_(10)H_(17)O_(3)占比最大,臭氧氧化α-蒎烯生成的过氧自由基C_(10)H_(15)O_(4)发生多步自氧化及双分子反应,生成含更高氧数的过氧自由基和闭壳产物,证实了α-蒎烯自氧化反应通道的重要性.现有大气化学机理可基本捕捉α-蒎烯臭氧化反应的产物分布,但不同氧化通道产物的相对占比受模型设置的反应速率和反应通道分支比影响存在较大不确定性.此外,氢摘取通道可能对OH自由基氧化α-蒎烯具有重要贡献,但机制待进一步探索.本研究展示的NH_(4)^(+)化学电离质谱技术,具有高灵敏度、高分辨率、低检测限等优点,特别是对中等氧化程度的闭壳产物和RO_(2)自由基的检测.未来,这套系统有望在更复杂的大气环境中揭示VOCs的演化规律和降解机制,为大气环境保护提供重要科学依据.
基金Project (2007CB613700) supported by the National Basic Research Program of ChinaProject supported by Research Program of Excellent Scholars Studying Abroad of Ministry of Human Resources and Social Security,China
文摘Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions with different concentrations（0.1%,0.5%,1.0%,3.5% and 5.0% in mass fraction） was evaluated by electrochemical measurements and immersion tests.The results showed that the corrosion rate of the MAO coated AZ91D increased with increasing chloride ion concentration.The main form of corrosion failure was localized corrosion for the MAO coated AZ91D immersed in higher concentration NaCl solutions（1.0%,3.5% and 5.0%）,while it was general corrosion in dilute NaCl solutions（0.1% and 0.5%）.Two different stages of the failure process of the MAO coated AZ91D could be identified：1） occurrence of the metastable pits and 2） growth of the pits.Different equivalent circuits were also proposed based on the results of electrochemical impedance spectroscopy（EIS） for the MAO coated AZ91D immersed in different concentrations of NaCl solutions for 120 h.
文摘Several recently developed analytical techniques, based on high-end mass spectrometry and chromatography, for dealing with challenges in petroleum characterization are reported. Folded flight path time-of-flight mass spectrometry provides resolving power up to 100000, enabling accurate mass measurement for molecular formula determination with high confidence. Atmos- pheric pressure chemical ionization （APCI） can be used in both gas chromatography （GC, as APGC） and liquid chromatog- raphy （LC） for analyzing non-polar hydrocarbons as well as polar compounds. The improvement in chromatography facilitates the mass spectrometric analysis through online coupling. Comprehensive two-dimensional gas chromatography （GCxGC） re- solves overlapping components, rendering accurate identification and quantitation. Supercritical fluid extraction has been de- veloped as an alternative method to replace traditional solvent extraction methods and eliminate the use of large volumes of solvents that can be harmful to health and environment. Supercritical fluid chromatography （SFC） has been developed as a convergence of GC and LC chromatographic techniques. The use of SFC for heavy oils and residua has been demonstrated. Prospective developments in the use of mass spectrometric and chromatographic methods for petroleum characterization are also described.
