Chromatographic methods for the determination of the logL16 solute descriptor

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 logL(16) 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 logL(16) to be estimated to +/- 0.026 log units over the temperature range 60-120 degreesC. Without correction for interfacial adsorption a single column estimation of logL(16) with phase loadings of 8 to 20% (m/m) over the temperature range 80-120 degreesC 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 logL(16) on the poly(methyloctylsiloxane) column requires prior knowledge of the solute dipolarity/polarizability descriptor to avoid significant errors in the measurement of logL(16) for polar compounds. In such circumstances a single column estimation of logL(16) over the temperature range 60-140 degreesC with an error of +/-0.05-0.09 log units is possible.