Isocratic retention data, HPLC

HPLC retention data for QSRR analysis are usually obtained by measuring log at several eluent compositions (isocratic conditions) and then extrapolating the dependence of log on a binary eluent composition to a fixed mobile phase composition, common for all the analytes studied, based on the Soczewinski-Snyder model ... 

Isocratic retention, prediction from gradient runs, 204-205 errors in, 209-211 ion-exchange HPLC, 206-208 reversed-phase HPLC 205-206 Isocmtic retention data, relationship to... 

The effect of temperature on the RP-HPLC behaviour of /(-carotene isomers has been extensively investigated and the results were employed for the separation of carotenoids of tomato juice extract. Carotenoids were extracted from food samples of 2g by adding magnesium carbonate to the sample and then extracted with methanol-THF (1 1, v/v) in a homogenizer for 5min. The extraction step was repeated twice. The collected supernatants were evaporated to dryness (30°C) and redissolved in methanol-THF (1 1, v/v). Separations were performed on a polymeric ODS column (250 X 4.6 mm i.d. particle size 5/.an). The isocratic mobile phase consisted of methanol-ACN-isopropanol (54 44 2, m/m). The flow-rate was 0.8 or 2.0 ml/min. The effect of temperature on the retention times of lycopene and four /(-carotene isomers is shown in Table 2.11. The data indicated that the temperature exerts a considerable influence on the retention time and separation of /(-carotene isomers. Low temperature enhances the efficacy of separation. 

In spite of many efforts, the relationships between retention and mobile phase composition are approximate. The fact is that often the values of logA extrapolated from several isocratic measurements in water-oiganic modifier eluents of varying compositions to the pure water eluent (the intercepts in Eq. (11.4)) are different from those determined experimentally (when it is possible). Besides. logA. data from the reversed-phase HPLC log A. data are often different when derived from aqueous systems modified with different organic solvents 117j. 

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