Distribution coefficients of n-alkanes measured on wall-coated capillary columns

Distribution coefficients K of n-alkanes were determined in wide ranges of temperature and carbon numbers from gas chromatographic retention data meas ured on wall-coated poly(dimethylsiloxane) commercial capillary columns. A discussion is centered on how to mitigate the difficulties for an accurate determination of K when using weakly retentive columns, as those bearing ve ry high phase ratios or short lengths. Particularly, the errors associated with the estimation of the gas hold-up and the phase ratio of the column ar e considered. The chromatographic importance for determining K of n-alkanes relies on the fact that these are the most commonly applied references for reporting relative thermodynamic parameters such as the Kovats Index and t he relative retention. A great amount of information has been compiled in t his farm. If K of the reference is known, absolute values of distribution c oefficients for a myriad of substances are readily obtainable. The knowledg e of K(T) functions of solutes in wide ranges of temperature is a primary n ecessity in temperature-programmed gas chromatography. This knowledge is ne eded for the prediction of absolute retention times and for computing separ ation optimizations of mixtures containing several critical pairs of analyt es. (C) 2000 Elsevier Science B.V. All rights reserved.