Studies on shape selectivity of RP C18-columns

Stationary phases with octadecyl groups have been prepared with different carbon content without and in the presence of water and characterized for their selectivity for the shape of various polyaromatic hydrocarbons. It is shown that both a high hydrocarbon content and a good accessibility of the bonded groups within the pores is required to achieve shape recognition for PAH. High carbon content alone is not sufficient. The two tests for shape selectivity proposed by Sander and Wise as well as by Tanaka are compared. In most cases the results are similar: A low selectivity with the Sander and Wise test (alpha TBN/BaP < 1) corresponds to a high value with the Tanaka test (alpha TRI/o-TER > 3). However, not in all cases the tests give corresponding answers. Further studies on molecular recognition are required.