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

External mass transfer coefficients (kf) were measured for a column packed with fully porous C18-silica spherical particles (50.6 μm 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 kf 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 1.8 × 103 to 2.7 × 103, respectively. We found that Sh is proportional to Reα and Scβ and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of α and β 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 kf values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of kf in HPLC systems, even for particle sizes of the order of a micrometer.