QUANTITATIVE STRUCTURE-RETENTION RELATIONSHIPS FOR THE INVESTIGATION OF THE RETENTION MECHANISM IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING APOLAR ELUENT WITH A VERY-LOW CONTENT OF POLAR MODIFIERS

The mechanism of the retention in HPLC when using a non-polar solvent with a very low content of polar modifier as mobile phase is outside t he scope of the classical interpretations. We have used quantitative s tructure-retention relationships (QSRR) to interpret the retention of a series of 36 compounds on 18 chromatographic systems (3 stationary p hases and 6 mobile phases). Principal Component Analysis (PCA) was use d to reduce the complexity of the data and to obtain the most signific ant axis; molecular modeling (molecular mechanics and molecular orbita l calculations) was used to obtain structural information on the solut es, and multiple regression to correlate coordinates and descriptors. We have shown that the coordinates of the solutes on the first PCA axi s are related to three molecular descriptors: the calculated logarithm of the partition coefficient in an octanol/water system (Log P), the polarisability (pol) and the energetic level of the highest occupied m olecular orbital (HOMO). We have found the same equation with a simila r coefficient for the three different stationary phases. These results prove the dominant role of the polar modifier in such chromatographic systems.