Retention Studies In HPLC

The effect of increasing temperature on retention time, efficiency and peak symmetry on a PS-DVB column was investigated using two sets of homologous compounds, phenylalkanols (benzyl alcohol to 5-phenylpentanol) and alkyl aryl ketones (benzaldehyde to heptanophenone) as standard compounds. It was found that efficiency and peak symmetry can be improved by an increase of temperature in both RP-HPLC and NP-HPLC In NP-HPLC, the use of a low level of polar organic modifier can reduce retention times and give improved peak shapes and column efficiencies. A different elution order was obtained in RP-HPLC compared with NP-HPLC The study was extended to retention prediction in RP-HPLC Retention indices can be calculated from the molecular structure of a compound as the sum of the parent index, substituent indices, and interaction indices. In this study the substituent contributions have been determined for 7 aromatic functional groups and 8 aliphatic functional groups over a range of methanol, acetonitrile and THF buffer eluents based on the alkyl aryl ketone retention index scale. The effect of intramolecular hydrogen-bonding in THF has been studied. A general prediction model was used for the retention prediction of disubstituted compounds. It was found -that the use of the Hammett constant (0") had its limitations and was not suitable if THF was the eluent.