Chromatographic methods for the determination of the logL16 solute descriptor

Abstract

A squalane packed column and two open-tubular columns coated with an immobilized stationary phase film of poly(dimethylsiloxane) or poly(methyloctylsiloxane) are evaluated as surrogate chromatographic systems for the determination of the logL16 solute descriptor by gas chromatography. Retention on the squalane column is dominated by gas-liquid partitioning with a significant temperature-dependent contribution from interfacial adsorption at the liquid-solid interface. Using the gas-liquid partition coefficient as the dependent model variable allows logL16 to be estimated to +/- 0.026 log units over the temperature range 60-120 degrees C. Without correction for interfacial adsorption a single column estimation of logL16 with phase loadings of 8 to 20% (m/m) over the temperature range 80-120 degrees C is possible for compounds with moderate hydrogen-bond basicity. The poly(dimethylsiloxane) stationary phase is both dipolar and hydrogen-bond basic and less suitable than the poly(methyloctylsiloxane) stationary phase, which is less cohesive and has similar dipolarity but no hydrogen-bond basicity. The determination of logL16 on the poly(methyloctylsiloxane) column requires prior knowledge of the solute dipolarity/polarizability descriptor to avoid significant errors in the measurement of logL16 for polar compounds. In such circumstances a single column estimation of logL16 over the temperature range 60-140 degrees C with an error of +/- 0.05-0.09 log units is possible.

The Use of Solvation Models in Gas Chromatography

“…While this method gave good results at high temperatures, the column was deactivated irreversibly within few hours. A probable explanation of this phenomenon is that the adhesion between apolane and the deactivated silica does not assure the film stability at higher temperature [24,27]. Our experience indicates that the use of commercially available apolane coated capillary columns should be limited to low temperature ranges.…”

“…This method making it possible to reduce considerably retention time was applied to determine vapor pressures of pesticides and polyaromatic hydrocarbons. Nevertheless, the stationary phase DB-1 is slightly polar [24]. Corresponding system parameters of the poly(dimethylsiloxane) immobilized in DB-1 column were published in the reference [24].…”

“…Moreover, it is very difficult to obtain absolute retention data using this technique. Li et al [24] and Abraham et al [25] studied influence of the solute support and of the stationary phase loading on adsorption phenomena. They concluded that the high loading ratio (up to 20 %) of the stationary phase and the high temperature of the column allow to reduce adsorption.…”

“…Experimental procedures of successive determination of LSER parameters were described in the literature [20,[22][23][24]. Log L 16 characterizes the most general interactions present in every physical system and should be determined before other parameters [24]. The original values of log Cavity formation Insertion of the solute Interactions Solute-Solvant L 16 were determined from retention data of organic compounds on n-hexadecane coated packed columns at 298.2 K [5].…”

“…Experimental procedures of successive determination of LSER parameters were described in the literature [20,[22][23][24]. Log L 16 characterizes the most general interactions present in every physical system and should be determined before other parameters [24].…”