VALIDITY OF A NOTION OF ELUENT FORCE TAKI NG INTO ACCOUNT THE NATURE OF THE GRAFT ON SILICA IN AQUEOUS AND NONAQUEOUS LIQUID-CHROMATOGRAPHY

An eluotropic scale accounting for the nature of the graft on silica w as established for different RPLC systems. By using a simple transfer rule, this eluotropic stationary bonded phase scale gives the appropri ate bonded chain length needed for a separation. The limits of the met hod are described. Monofunctional bonded silicas such as C-1, C-6, C-8 , C-11, C-12, C-14, C-18, C-22 and phenyl were studied. This was done in pure water, in different rich organic modifier mobile phases (MeOH- H2O, MeCN-H2O) as well as in mobile phases commonly used in non aqueou s reversed phase liquid chromatography 'NARP' (MeCN / CHCl3, MeCN / TH F, MeCN / AcMe and MeCN / CH2Cl2). The comparison has been made using methylene selectivity obtained from the results of the homologous seri es analysis. Two eluotropic scales were also established for partially -aqueous mobile phases on phenyl-bonded silica and non-aqueous mobile phases on C-18-bonded silica. In general it is shown that the more sel ective systems are those using C-14-alkyl-bonded chains. Moreover the particular behavior of C-14-bonded silicas in pure water may be noted.