Similarity of RP-Phases

As explained above, in the author s opinion, for a separation technique such as HPLC selectivity is the most impoitent and most expressive criterion for the comparison of columns or for establishing the similarity of RP-phases. Retention factors should only be considered as a secondary issue. To verily this, a chemo-metric analysis (see below) was performed with a large number of data (very different separation conditions and different analytes) see Fig. 18. The further the variables (here, k and a values) are from the origin on the y-axis, the stronger is their influence on the differentiation of objects, which here means columns. 

As can easily be seen, the a values are indeed suitable for this. If, nevertheless, one wants to use k values, then problematical compounds are best suited for this, e.g., polar analytes in tmbuffered eluents (e.g., k Cos, caffeine) or strong acids in buffered eluents (k Phs, phthalic add and k Tes, terephthalic acid). 

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