A SIMPLE-MODEL DESCRIBING THE RETENTION BEHAVIOR OF OCTREOTIDE AND ITS GLYCOSYLATED DERIVATIVES IN REVERSED-PHASE HPLC

The retention behavior of octreotide, a somatostatin analogue, and its glycosylated derivatives containing different numbers of glucose unit s has been studied by reversed phase HPLC. A retention model was devel oped by correlating the logarithm of the retention factor with the hyd rophilic-lipophilic balance of the analyte. Linear functions could be derived for all the separation systems investigated. The slopes of the straight lines were a measure of the selectivity of the chromatograph ic system and enabled calculation of increments for the saccharide gro ups in different eluent systems. The highest increment was found using trifluoroacetic acid (TFA) as ion pairing agent. The model was extend ed to substitution of the same peptide with hydrophobic groups such as acetyl and alkyl. Straight lines were again obtained. The influence o f the different eluent systems upon peak shape and retention is also d iscussed. Owing to the strong peak tailing a dual retention mechanism consisting of hydrophobic and silanophilic interactions was assumed. I t was shown that addition of quaternary ammonium compounds to mask the surface silanols of the stationary phase reduced both the peak tailin g and the retention of the peptides.