The Thermodynamics of Chromatography - Interactions Between the Atoms of Hydrogen, Carbon, Chlorine and Bromine and an Exclusively Dispersive Stationary Phase > Experimental Data > Page 33

 

In figure 12 they are shown to have very similar slopes (0.402 and 0.406) and significantly different intercepts (1.193 and 2.002). Comparing equations (19) and (20) it is seen that each curve should exhibit the same intercepts, namely () but different slopes () and (). The calculated values of the intercepts are1.193 and 1.173, and the slopes are very different vis. 0.402 and 0.819.

Figure 12 Graph of Log(Distribution Coefficient) against Number of Substituent Groups in Methane

  

 

The distribution coefficients measured at different temperatures can be used to identify the various thermodynamic parameters {i.e., (DG'H), (DG'C), (DG'Cl) and (DG'Br)} with the aid of a computer and a simple iterative program. Values for each parameter can be taken over a wide numerical range and used in equations (2) to (11) to calculate the log(K). Each calculated value can then be subtracted from that obtained experimentally and the difference squared and summed for all the ten equations. Each time the sum is reduced, the particular values of each parameter are noted, and the process is continued until those values for the parameters that provide the minimum sum of squares is obtained. The value of each parameter calculated in this manner are given in table 2.