Prediction of Retention Times from log

The prediction of retention times in a given eluent from log P has been proposed for aromatic hydrocarbons.19 The log A values of phenols21 and nitrogen-containing compounds22 were also related to their logP, and the calculated log P was used for the qualitative analysis of urinary aromatic acids, i.e. for the identification of metabolites in urine from the differences of log P in reversed-phase liquid chromatography.23,24 

A good correlation was obtained in 20-80% acetonitrile-water mixtures. The standard non-ionic compounds used to evaluate the columns were 2-hydroxy-acetophenone, coumarin, acetophenone, indole, propiophenone, butyro-phenone, isopropyl benzoate, butyl benzoate, and isopentyl benzoate. The plotted lines for the linear relationship measured in five different proportions 

Further, an optimization of the organic modifier concentration for the separation of known compounds was proposed. When the value of the actual column plate number, the resolution, and log P of pairs of compounds a and b were known, the percentage concentration (x) required for their separation was calculated from Equations 6.4 to 6.6 19,20 

Prediction of Retention Time of Ionic Compounds from log P and pKa 

The retention times of neutral non-ionized compounds can be predicted by the above calculation method, but those of ionized compounds are also very important. The inclusion of the dissociation constant in the calculation made it possible to predict the retention times of ionized aromatic acids.25,26 The dissociation constant was calculated by the method proposed by Perrin et al.27 

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Prediction of Retention Times from log P in Reversed-phase Liquid Chromatography... 

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