Chattopadhyay S, Tobias H J, Ziemann P J
Air Pollution Center, University of California, Riverside 92521, USA.
Anal Chem. 2001 Aug 15;73(16):3797-803. doi: 10.1021/ac010304j.
A temperature-programmed thermal desorption method for measuring vapor pressures of low-volatility organic aerosol compounds has been developed. The technique employs a thermal desorption particle beam mass spectrometer we have recently developed for real-time composition analysis of organic aerosols. Particles are size selected using a differential mobility analyzer, sampled into a high-vacuum chamber as an aerodynamically focused beam, collected by impaction on a cryogenically cooled surface, slowly vaporized by resistive heating, and analyzed in a quadrupole mass spectrometer. A simple evaporation model developed from the kinetic theory of gases is used to calculate compound vapor pressures over the temperature range of evaporation. The data are fit to a Clausius-Clapeyron equation to obtain a relationship between vapor pressure and temperature and to determine the heat of vaporization. The technique has been evaluated using C13-C18 monocarboxylic and C6-C8 dicarboxylic acids, which have vapor pressures at 25 degrees C of approximately 10(-4) - 10(-6) Pa, but less volatile compounds can also be analyzed. The method is relatively simple and rapid and yields vapor pressures and heats of vaporization that are in good agreement with literature values. The technique will be used to generate a new database of vapor pressures for low-volatility atmospheric organic compounds.
已开发出一种程序升温热脱附方法，用于测量低挥发性有机气溶胶化合物的蒸气压。该技术采用了我们最近开发的用于有机气溶胶实时成分分析的热脱附粒子束质谱仪。使用差动迁移率分析仪对颗粒进行尺寸筛选，将其作为空气动力学聚焦束采样到高真空室中，通过撞击收集在低温冷却表面上，通过电阻加热缓慢蒸发，并在四极质谱仪中进行分析。基于气体动力学理论开发的简单蒸发模型用于计算蒸发温度范围内化合物的蒸气压。将数据拟合到克劳修斯 - 克拉佩龙方程，以获得蒸气压与温度之间的关系，并确定汽化热。已使用C13 - C18单羧酸和C6 - C8二羧酸对该技术进行了评估，这些化合物在25℃下的蒸气压约为10(-4) - 10(-6) Pa，但挥发性更低的化合物也可进行分析。该方法相对简单快速，所得蒸气压和汽化热与文献值高度吻合。该技术将用于生成低挥发性大气有机化合物蒸气压的新数据库。
