Optimum, column, capacity ratio

Whether the optimum phase system is arrived at by a computer system, or by trial and error experiments (which are often carried out, even after computer optimization), the basic chromatographic data needed in column design will be identified. The phase system will define the separation ratio of the critical pair, the capacity ratio of the first eluted peak of the critical pair and the capacity ratio of the last eluted peak. It will also define the viscosity of the mobile phase and the diffusivity of the solute in the mobile phase. 

It is clear that the major factor controlling the particle diameter will be the separation ratio (a), which reflects the difficulty of the separation. The more difficult the separation, the more theoretical plates are needed, and thus the column must be longer. However, to use a longer column, the particle diameter must be increased to allow the optimum velocity to be realized without exceeding the maximum system pressure. The effect of the capacity ratio of the first solute of the critical pair on the optimum particle diameter is complex. Extracting the function of the capacity ratio (f(k )) from equation (1),... 

Equation 6 Calculation of optimum ratio of particle size and column length, with selectivity factor, a capacity factor of second component of critical pair under analytical chromatography conditions, fe 02 diffusion coefficient, (cm /s) (typical value for MW 1000 10 cm /s) viscosity, p (cP) specific permeability (1.2 X 10 for spherical particles), feo third term of the Knox equation, C and maximum safe operating pressure, Ap, (bar). 

Optimum experimental conditions for maximum production rate at various specified values of the recovery yield. Experimental conditions a = 1.2, fcg j = 3 column saturation capacity = phase ratio, F = 0.25 maximum available pressure, AP = 100... 

The solute capacity factors measured at the optimum linear carrier velocity increase monotonously as the inverse of the column diameter, as shown in Figure 2. This result is to be expected, since the phase ratio decreases in the same fashion. However, since the mobile-phase volume decreases geometrically x on reducing the column radius, raw analysis times for a givmi linear carrier velocity, while longer with the columns of smaller ID, are not inordinately so. The values of tjjm (min m ) for columns 1 to 6 respectively were 2.38, 2.56, 2.62, 2.6 3.03, 3.63, while column 7 gave 3.14 (see below). 

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