The solvation parameter model is used to identify suitable chromatographic models for estimating the octanol-water partition coefficient for neutral compounds of varied structure by reversed-phase liquid chromatography. The stationary phase Supelcosil LC-ABZ with methanol-water mobile phases affords a series of suitable correlation models for estimating the octanol-water partition coefficient (log KOW) under isocratic and gradient elution conditions. Isocratic separations with mobile phase compositions containing from about 25 to 40% (v/v) methanol provide the most accurate results for log KOW values in the range -0.1 to 4.0. Gradient separations programmed from 5 to 100% (v/v) methanol are suitable for faster separations of compounds with large log KOW values. The standard error in the estimate for the regression models of the predicted log KOW values against literature values are 0.135 log units for the 30% (v/v) methanol-water isocratic system and 0.263 log units for the methanol-water gradient system. Isocratic retention factors predicted from two gradient separations with gradient times of 15 and 45 min afford a poorer fit for the correlation models between log KOW and the estimated retention factors than that of either the above isocratic and gradient models. Plots of the retention factor (log k) as a function of mobile phase composition are generally non-linear. Values of log kw obtained by non-linear extrapolation to a volume fraction of 0% (v/v) methanol do not afford a useful model for estimating log KOW.

SummaryThe solvation parameter model is used to determine the system constants for four poly(dimethyldiphenylsiloxane) and a poly(cyanopropylmethylsiloxane) stationary phase at five equally spaced temperatures in the range 60-140 ~ Together with literature data for other poly(dimethyldiphenylsiloxane) stationary phases it is shown that the introduction of from 0 to 65% diphenylsiloxane groups into a poly(dimethylsiloxane) polymer influences selectivity through an increase in dipolarity/polarizabihty and hydrogen-bond basicity Changes in cohesion with variation in composition are small and electron lone pair interactions are weak and only significant at the higher end of the temperature range studied. The changes in system constants with composition are pseudo-linear for incorporation of less than 50% diphenylsiloxane groups. Higher incorporation of diphenylsiloxane groups as multimers results in a different contribution to selectivity The influence of temperature is to decrease the system constants with increasing temperature in an approximately linear manner. The poly(cyanopropylmethylsiloxane) stationary phase is significantly more cohesive, dipolar/polarizable and hydrogen-bond basic than the poly(dimethyldiphenylsiloxane) stationary phases.A notable feature of this stationary phase is the shallow change in the system constant for dipole-type interactions with temperature compared to the other system constants. A comparison of the properties of the poly(cyanopropylmethylsiloxane) stationary phasewith a poly(cyanopropylphenyldimethylsiloxane) stationary phase is made to provide a qualitative picture of the influence of the phenyl g rou p on the selectivity of cyanopropyl-containing stationary phases.

Non-specific retention characteristics of dissolved b-cyclodextrin derivatives in open tubular column gas chromatographyThe solvation parameter model is used to identify contributions from intermolecular interactions responsible for non-specific retention in gas chromatography for three dissolved b-cyclodextrin derivatives in a poly(cyanopropylphenyldimethylsiloxane) stationary phase. The cyclodextrins are permethylated b-cyclodextrin (Cyclodex-B), heptakis(2,3-di-O-methyl-6-O-t-butyldimethylsilyl)-b-cyclodextrin (CycloSil-B) and heptakis(2,3-di-O-acetoxy-6-O-t-butyldimethylsilyl)-b-cyclodextrin (Rt-bDEXsa). Taking DB-1701 as a reference phase for the poly(cyanopropylphenyldimethylsiloxane) solvent, it is shown that the dominant interactions for the cyclodextrin derivatives are associated with their hydrogen-bond basicity and capacity for dipole-type interactions. None of the cyclodextrin derivatives are hydrogen-bond acids and all are weakly electron lone pair repulsive. The cohesive properties of the dissolved phases are similar to those of the solvent, except for Rt-bDEXsa, which is significantly more cohesive. Also, Rt-bDEXsa shows significant inclusion complexation for the compounds used to determine the system constants of the solvation parameter model resulting in poor statistical models, suitable only for qualitative interpretation. The Cyclodex-B and CycloSil-B columns are compared to a database of 23 open-tubular column stationary phases possessing similar selectivity to each other but different selectivity for non-specific interactions to the other stationary phase types.

Influence of composition and temperature on the selectivity of stationary phases containing either mixtures of poly(ethylene glycol) and poly(dimethylsiloxane) or copolymers of cyanopropylphenylsiloxane and dimethylsiloxane for open-tubular column gas chromatography The solvation parameter model is used to determine the system constants for three columns containing mixtures of poly(dimethylsiloxane) and poly(ethylene glycol) and a poly(cyanopropylphenyldimethylsiloxane) containing 6% of cyanopropylphenylsiloxane monomer at five equally spaced temperatures in the range 60 -1408C. Together with literature data for a poly(dimethylsiloxane) and a poly(ethylene glycol) stationary phase the influence of temperature and composition on selectivity is studied for mixing ratios of 0 to 1 poly(ethylene glycol) for the temperature range 60 -1408C. Using literature data for two poly(cyanopropylphenyldimethylsiloxane) stationary phases containing 14% and 50% of cyanopropylphenylsiloxane monomer groups the influence of temperature and replacing dimethylsiloxane monomer groups by cyanopropylphenylsiloxane groups on selectivity is studied for incorporation of 0 to 0.5 cyanopropylphenylsiloxane groups over the temperature range 60 -1408C. Addition of poly(ethylene glycol) or introduction of cyanopropylphenylsiloxane monomer groups into a poly(dimethylsiloxane) influences selectivity through an increase in dipolarity/ polarizability, hydrogen-bond basicity, electron lone pair interactions, and changes in cohesion. The changes in system constants as a function of temperature and composition are simply modeled as smooth quadratic response surfaces. Curvature in the response surfaces along the composition axis is significant while changes along the temperature axis are modest for both stationary phase types. Cluster analysis is used to demonstrate that the mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phases containing 0.5 and 0.85 weight fraction of poly(ethylene glycol) have different selectivity to a database of common open-tubular column stationary phases. The mixed poly(dimethylsiloxane)/poly(ethylene glycol) stationary phase containing 0.10 weight fraction of poly(ethylene glycol) has similar selectivity to the poly(cyanopropylphenyldimethylsiloxane) containing 6% cyanopropylphenyl monomer groups, and could replace the mixed phase for all but the most critical of separations.