INFLUENCE OF THE INJECTED SAMPLE COMPOSITION ON THE RETENTION PARAMETERS OF POLAR COMPOUNDS UNDER ZIC-HILIC MECHANISM IN LIQUID CHROMATOGRAPHY

This study is focused on the influence of the sample composition and volume on the retention of two tested compounds (glycyl-L-leucine and glycyl-L-alanine) under zwiterionic hydrophilic liquid chromatography mechanism (Zic-Hilic), using a column loaded with zwitterionic sulfobetaine covalently attached to porous silica as stationary phase. A standard mobile phase composition was used (80% acetonitrile and 20% aqueous component with various contents of ammonium acetate) for investigating the possible retention modifications of studied compounds (retention time and peak shape) when sample diluent was identical or different to the composition of the mobile phase. It was shown that small variations in the composition of the injected solvent do not affect significantly the retention parameters (retention factor, peak efficiency and simmetry) of the tested compounds, when the injected volume was at most 20 mu L. Higher injected volumes (50 mu L) can influence the retention of the less retained compound, glycyl-L-leucine, while the more retained compound, glycyl-L-alanine, is not influenced by the modification of the concentration of ammonium salt in sample diluent.