Test to evaluate countercurrent chromatographs - Liquid stationary phase retention and chromatographic resolution

Countercurrent chromotography (CCC) is a liquid chromatography (LC) techniq ue with a special column able to retain a liquid stationary phase while the liquid mobile phase is pumped through. The coil planer centrifuge machines are made of open tube wound on spools. A simple test is proposed. The meth anol-water (90:10, v/v)-heptane biphasic system is used with heptane as the mobile phase in the ascending or tail-to-head mode. The methanol-water sta tionary phase retention volume is measured at different Bow-rates and rotor rotation speeds. After every machine equilibration, an alkylbenzene mixtur e is injected and the retention factors, peak efficiencies and resolution f actors are measured or calculated for each solute. The wealth of informatio n contained in the data set obtained is demonstrated, Four coil planer cent rifuge machines of very different characteristics and one hydrostatic CCC m achine with channels and ducts were submitted to the test. it was shown tha t the Sf, stationary retention factor, obtained with these machines was lin early dependent on the square root of F, the mobile phase how-rate [Q. Du, C. Wu, G. Qian, P. Wu, Y. Ito, J. Chromatogr. A 835 (1999) 231-235]. It is shown that the slopes of the Sf versus F-1/2 lines could be related to a mi nimum rotor rotation, omega (mini), necessary to obtain the hydrodynamic eq uilibrium. The Sf and F parameters give the mobile phase linear velocity, i i. It is shown that u is proportional to the square root of omega, the roto r rotation speed. The slope and intercept of the latter relationship also r esult in omega (mini) value coherent with the first one. With the peak effi ciencies and chromatographic resolution factors obtained for toluene and he xylbenzene, the parameters: number of plates per tubing turn, machine volum e for one plate, and tubing length for one plate, were calculated and compa red for the five machines. The internal diameter of the tubing used is show n to be a critical parameter acting on the machine volume and number of tub ing turns. (C) 2000 Elsevier Science B.V. All rights reserved.