Use of solid-phase microextraction for measuring oil-water partition coefficients and correlation with high-performance liquid chromatographic methods for lipophilicity

For flavour compounds, lipophilicity is often estimated by the partition co efficient between oil and water (log Koil-water), which is highly relevant to food. A modification of the shake-flask method is reported here where co mpounds are quantified in the two phases using solid-phase microextraction (SPME). SPME's highly sensitivity to non-polar compounds facilitates quanti fication in the water phase. Twelve flavour compounds representing a broad range of lipophilicities and functional groups were analysed by two methods . Their log Koil-water was determined using SPME quantitation and their log k(w) using a reversed-phase HPLC methodology. The isocratic capacity facto r at 60% methanol and predicted log P value also showed high correlation fa ctors with other methods. The octadecyl silylated surface of the HPLC colum n provides a matrix that interacts with lipophilic compounds where thr rete ntion time is the indication of lipophilicity. Both methods gave reproducib le results (median 3% and 4% RSD) and similar bur not identical values for lipophilicity. The relationship between the two methods is log k(w) = 0.85 log Koil-water + 0.48 with a correlation coefficient of 0.94. The new SPME detection method, with the ability to quantify limonene and 2-pentylfuran a t 1 ppm in the water phase, is preferred for flavour compound analysis due to the applicability of oil-water partitioning in food. (C) 1999 Elsevier S cience B.V. All rights reserved.