Organic phase change compounds

THF and methanol employed as organic modifiers of mobile phase provided a considerable difference in selectivity based on the polar interactions between solutes and the organic solvent molecules in the stationary phase. Acidic compounds, phenols and nitroaromatics, were preferentially retained in the THF-based mobile phase, whereas esters and ketones were preferentially retained in the methanol (a hydrogen-bond donor) containing mobile phase. The system presented here seems to be very practical because any laboratory possessing two sets of HPLC equipment and two C j g columns can attempt similar 2D HPLC by simply changing the mobile phase for the two dimensions. 

Secondly, the pH can have an effect on the selectivity. In pharmaceutical analysis, mainly compounds with either basic or acidic properties have to be analyzed. Since the pH influences the dissociation and charge of these substances, it will affect their retention behavior. Changing the organic modifier does not lead to major selectivity differences, but it can enhance the differences induced by pH and/or stationary phase changes. Also, the column... 

It is generally possible to study the effects of changes of state on the intramolecular and intermolecular forces In inorganic and organic compounds by investigating the variations in the vibrational spectra with decreasing temperature as the gas phase changes to the liquid and then to the solid state. 

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