Influence of microwave irradiation on the mass-transfer kinetics of propylbenzene in reversed-phase liquid chromatography

The effect of microwave irradiation on the kinetics of mass transfer in reversed-phase liquid chromatography (RPLC) was studied by measuring its influence on the band profile of propylbenzene in a C-18-silica column eluted with an aqueous solution of methanol and placed inside a microwave oven. The elution peaks were measured by the pulse-response method, under linear conditions. The amount of microwave energy induced into the column was varied based on the microwave input power. The experimental data were analyzed using the conventional method of moment analysis and the lumped pore diffusion model. With input powers of 15 and 30 W, the effluent temperatures were 25 +/- 1 and 30 +/- 1 degrees C, respectively. The effect of microwave irradiation on the mass transfer of the studied solute was determined by comparing the band profiles obtained under the same experimental conditions, at the same temperature, with and without irradiation. The values of the intraparticle diffusion coefficient, D-e, measured with microwave irradiation were ca. 20% higher than those obtained without irradiation. Derived from the method of moments, the values of De at 15 W (25 +/- 1 degrees C) and 0 W (25 +/- 1 degrees C) were 8.408 x 10(-6) cm(2) s(-1) and 6.947 x 10(-6) cm(2) s(-1), respectively, while these values at 30 W (30 +/- 1 degrees C) and 0 W (30 +/- 1 degrees C) were 9.389 x 10(-6) cm(2) s(-1) and 7.848 x 10(-6) cm(2) s(-1), respectively. The values of the surface diffusivity, D-S, also increased with increasing power of the microwave irradiation. It is assumed that the increase in intraparticle diffusion for propylbenzene was caused by the molecular excitation of the organic modifier that has a higher dielectric loss than the solute. The values of D-e, were also analyzed and determined using the POR model. There was an excellent agreement between the results of the two independent methods. These preliminary results suggest that microwave irradiation may have a considerable influence on the mass transfer kinetics in RPLC.