Linear and Quadratic Relationships between Retention and Organic Modifier Content in Eluent in Reversed Phase High-Performance Liquid Chromatography: A Systematic Comparative Statistical Study

Abstract

Statistical evaluation of linear and quadratic models of chromatographic retention was performed. The relationships describing retention were derived for a set of 23 carefully selected test analytes chromatographed on 18 HPLC columns using methanol‐water or acetonitrile‐water solutions as mobile phase. It was ascertained whether the square term in the quadratic model improves the description of chromatographic retention in a statistically significant manner. It was also checked whether the retention data extrapolated to a hypothetical neat water eluent (log kw) obtained with the two models and the two organic modifiers are equivalent or should be considered different. The research proved that both models yield similar results and the extrapolated log kw values do not differ statistically significantly in the case of methanol‐containing mobile phases. In the case of acetonitrile‐water systems the log kw values obtained with linear and quadratic models are normally statistically different. Correlation analysis for log kw vs. log P parameters was performed for data determined on six columns. The best correlations were achieved employing log kw data derived with the linear model for methanol/water systems.

Separation methods for estimating octanol–water partition coefficients

“…where φ is the volume fraction of organic solvent (binary mobile phase), S the slope of the experimental data after fitting to a linear regression model (not to be mistaken for the solute descriptor S used in connection with the solvation parameter model), and a 1 and a 2 are regression constants for the second order model, which are not usually assigned any physical significance [9,27,[50][51][52][53][54][55]. If it is assumed that the mobile phase composition range used to define the relationship for the extrapolation is unimportant, then log k W values can be obtained for compounds with a wider range of retention properties than is possible for a single mobile phase composition.…”

Chromatographic Approaches for Measuring Log P

“…However, several studies on different stationary phases showed statistical differences for this parameter when using either methanol or acetonitrile [7,32] . This phenomenon is probably due to the stationary phase solvation which differs with the organic modifi er.…”

Relating chromatographic retention and electrophoretic mobility to the ion distribution within electrosprayed droplets

“…The results from our determination of the retention factors for the model compounds are shown in Figure 3. A plot of log k versus organic modifier content in the mobile phase for a limited organic modifier range should give a straight line with a negative slope if only one type of interaction is present [11]. However, in our LC experiments, deviations from this theory were obtained for low retention values (data not shown).…”