USE OF ORTHOGONAL COLLOCATION ON FINITE-ELEMENTS WITH MOVING BOUNDARIES IN THE SIMULATION OF NONLINEAR MULTICOMPONENT CHROMATOGRAPHY - INFLUENCE OF FLUID VELOCITY VARIATION ON RETENTION TIME IN LC AND HPLC

Two numerical procedures for the solution of a non-linear multicompone nt chromatography model have been developed. The applied model include s axial dispersion in the external fluid phase, interphase mass transf er resistances and variation of fluid velocity. First solution techniq ue is based on the method of lines, in which the space variables are d iscretized using the orthogonal collocation method on moving finite el ements, coupled with an integration method for stiff ordinary differen tial equations. An efficient procedure for updating during the integra tion of the position of the finite element boundaries, in order to fol low the movement of peaks, is proposed. Second solution technique is a very fast finite difference method. The influence of fluid velocity v ariation on retention time for liquid chromatography (LC) and high per formance liquid chromatography (HPLC) is presented.