Selecting Columns of Very Different Selectivity

During RP LC method development, a need for a change in separation selectivity is often encountered [20], Similarly, in some cases there is a need for orthogonal separation, where a very different column selectivity can be used to check for the 

Type B C]g or Cg column type A Cjg column embedded polar group column polar end-capped column cyano column phenyl column  

An imderstanding of column selectivity is important for various reasons, but mainly when it is necessary to replace one column by another with either similar or very different selectivity. Column selectivity can be accurately characteri2 ed by five measurable properties of the column H, Hydrophobidty S, Steric resistance to insertion of bulky solute molecules into the stationary phase A, column hydrogen-bond Acidity B, column hydrogen-bond Basicity C, column Cation-exchange activity. Values of these column parameters (H, S, etc.) have now been measured for a large number of different RP LC columns. Given values of H, S, etc., it is possible to compare two columns in terms of selectivity by means of a column-comparison function F. Commercial software is available (Column Match Rheodyne LLC, Rohnert Park, CA, USA) that facilitates the convenient comparison of any two columns in terms of selectivity the software also includes values of H, S, etc. for about 300 different columns. 

P relative solute hydrogen-bond basicity (Eq. 2) p2 solute hydrogen-bond basicity in solution (Eq. 1) 

V free energy associated with creating a cavity in the stationary phase (Eq. 1) 

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