Department of Chemistry, Michigan State University, East Lansing, MI, 48824, USA.
Department of Chemistry, Michigan State University, East Lansing, MI, 48824, USA; Forensic Science Program, School of Criminal Justice, Michigan State University, East Lansing, MI, 48824, USA.
Anal Chim Acta. 2021 Oct 16;1182:338932. doi: 10.1016/j.aca.2021.338932. Epub 2021 Aug 10.
A kinetic model was previously developed in our laboratory to predict evaporation of compounds as a function of gas chromatographic retention index (I). To define the initial model, evaporation rate constants were experimentally determined for compounds in the range I = 800-1400 at temperatures from 5 to 35 °C. While the predictive accuracy was demonstrated, broader application of the model requires extension of the I range to include more volatile compounds. However, such extension requires experimental determination of rate constants, which is challenging due to the explosive hazard and rapid evaporation of volatile compounds. In this work, rate constants of highly volatile compounds were experimentally determined and used to extend the kinetic model to predict evaporation. Prior to experimental evaporations, theoretical calculations were performed to optimize experimental parameters and to ensure that the vapor generated remained below the lower flammability limit for each compound. Compounds were then experimentally evaporated at three different temperatures (10, 20, and 30 °C) and analyzed by gas chromatography-mass spectrometry. The evaporation rate constants for each compound, corrected for condensation, were determined by regression to a first-order rate equation. These rate constants were combined with previously collected data to extend the kinetic model at each temperature. Comparison of predicted and experimentally determined chromatograms of an evaporated validation mixture indicated good model performance, with correlation coefficients ranging from 0.955 to 0.997 and mean absolute percent errors in predicting abundance ranging from 3 to 26%.
先前，我们实验室开发了一个动力学模型，用于预测化合物的蒸发速率作为气相色谱保留指数（I）的函数。为了定义初始模型，我们在 5 至 35°C 的温度范围内，实验测定了 I 值在 800-1400 范围内的化合物的蒸发速率常数。虽然证明了该模型的预测准确性，但要更广泛地应用该模型，需要将 I 值范围扩展到包括更易挥发的化合物。然而，这种扩展需要实验测定速率常数，由于挥发性化合物的爆炸危险和快速蒸发，这是具有挑战性的。在这项工作中，我们实验测定了高挥发性化合物的速率常数，并将其用于扩展动力学模型以预测蒸发。在进行实际蒸发实验之前，我们进行了理论计算，以优化实验参数，并确保生成的蒸汽对于每种化合物都保持在其下限可燃性极限以下。然后，将化合物在三个不同的温度（10、20 和 30°C）下进行实验蒸发，并通过气相色谱-质谱进行分析。通过回归到一级速率方程，对每个化合物的校正冷凝后的蒸发速率常数进行了确定。将这些速率常数与先前收集的数据相结合，以在每个温度下扩展动力学模型。对蒸发验证混合物的预测和实验确定的色谱图进行比较表明，模型性能良好，相关系数范围为 0.955 至 0.997，预测丰度的平均绝对百分比误差范围为 3 至 26%。
