Characteristic thermal constant and dimensionless heating rate. The links to optimum heating rate in GC
Characteristic thermal constant and dimensionless heating rate. The links to optimum heating rate in GC
复制标题
特征热常数和无量纲加热速率。
作者：
Blumberg;Klee
在寻求获得一个通用的方法来优化的温度程序在气相色谱的第一步。其核心是引入无因次加热速率r。作为第一步定义r，一个特征热常数，thetachar，定义为thetachar = -dT/dk在k = 1，其中T和k分别是，柱温和溶质保留因子，引入和评估我们自己的实验数据和文献中的热力学数据。据确定，对于具有250的相比率的硅酮固定相，thetachar的范围从低分子量烃（例如二甲基丙烷）的约23摄氏度到高分子量农药（例如灭蚁灵）的约45摄氏度。有人还发现，对于一个特定的溶质和固定相类型，2个数量级的膜厚度的增加导致只有约2倍的特征热常数的增加。使用thetachar作为一个基本的温度单位，在GC和空时间作为一个基本的时间单位，无量纲的加热速率的介绍和其潜在的效用，在程序升温GC的分离速度的权衡评估证明。
An initial step in the quest of deriving a generalized approach to optimization of a temperature program in gas chromatography is presented. Central to this is the introduction of a dimensionless heating rate, r. As a first step to defining r, a characteristic thermal constant, thetachar, defined as thetachar = -dT/dk at k = 1, where T and k are, respectively, column temperature and solute retention factor, is introduced and evaluated for our own experimental data and for thermodynamic data from the literature. It was determined that, for silicone stationary phases with a phase ratio of 250, thetachar ranged from about 23 degrees C for low molecular weight hydrocarbons such as dimethylpropane to about 45 degrees C for high molecular weight pesticides such as mirex. It was also found that, for a particular solute and a stationary phase type, a 2 orders of magnitude increase in the film thickness caused only about a 2-fold increase in the characteristic thermal constant. Using thetachar as a fundamental temperature unit in GC and void time as a fundamental time unit, a dimensionless heating rate is introduced and its potential utility for the evaluation of the separation-speed tradeoffs in a temperature-programmed GC is demonstrated.