Kinetic study on external mass transfer in high performance liquid chromatography system

Abstract

External mass transfer coefficients (k(f)) were measured for a column packed with fully porous C(18)-silica spherical particles (50.6 microm in diameter), eluted with a methanol/water mixture (70/30, v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min(-1). Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k(f) for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh) was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8x10(3) to 2.7x10(3), respectively. We found that Sh is proportional to Re(alpha) and Sc(beta) and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of alpha and beta were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson-Geankoplis equation to estimate k(f) values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k(f) in HPLC systems, even for particle sizes of the order of a micrometer.