Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 82

Table 2

Experimental Values for the Dispersion Equation Coefficients Obtained by a Curve Fitting Procedure

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n-pentane      n-hexane       n-heptane     n-octane       n-nonane       n-decane

4.7%w/w     4.9%w/w       4.3%w/w      4.5w/w       4.4%w/w       4.85w/w

Et.Acet.       Et.Acet          Et.Acet.       Et.Acet.       Et.Acet.        Et.Acet.

The Van Deemter equation   

A 0.001189   0.001144      0.001144      0.001210      0.001208     0.001237

B 0.000108   0.000091      0.000081      0.000065      0.000049     0.000045

C 0.002525   0.003008      0.003362      0.003661      0.004298     0.004786    

The Giddings equation 

A 0.001189   0.001144       0.001123      0.001210     0.001407      0.001257

B 0.000108   0.000091       0.000086      0.000065     0.000067      0.000053

C 0.002525   0.003008       0.003348      0.003661     0.004001      0.004754

D 0              0                  0.005243      0                0.0337         0.008100

The Huber equation      

A 0.001455  0.001408        0.000986      0.001196     0.000702      0.1612

B 0.000104  0.000092        0.000084      0.000065     0.000057      0.000056

C 0.003302  0.002728        0.002979      0.003622     0.002769      0.002310

D -0.00092  0.000331        0.000447      0.000046     0.001775      -0.06804

E 0             0                  0                  0                0                 2.13100

The Knox equation     

A 0.002509  0.002422        0.002390      0.002545     0.002608      0.002626

B 0.000123  0.000105        0.000096      0.000080     0.000064      0.000061

C 0.008720  0.001407        0.001754      0.002003     0.002518      0.002304

The Horvath equation     

A 0.001366   0.001507       0.001013      0.001197     0.000825      0.005583

B 0.000104   0.000092       0.000083      0.000065     0.000056      0.000051

C 0.003572   0.002495       0.002744      0.003585     0.001948      0.009169

D-0.00110    0.000541       0.000647      0.000080     0.002454      -0.008577

E 0             0                  0                 0                 0                  97.30                      

 Furthermore, for the Huber equation, the value of coefficient (E) is consistently zero and for the Horvath equation, is zero for four solvents mixtures out of six, with an extreme value of 97.3 for one solvent.

On the basis of the irrational fits of the data to the Huber and Horvath equations, these equations will not be considered to satisfactorily describe the relationship between (H) and (u). According to Katz et al.  the same irrational behavior of the Huber and Horvath equation was observed if the data for hexamethylbenzene was also fitted to them.