Q: Regarding the issue of reducing the mixer capacity in accordance with a reduction in column size, is it not sufficient to just reduce the capacity of a standard mixer (minimum capacity: 0.5 mL)?
In gradient analysis, the system capacity in the section going from the gradient mixer to the column affects peak separation in the form of gradient delay. In switching to ultrafast analysis, reduce this system capacity in accordance with the reduction in capacity of the column.
If you continue to use the gradient mixer of a standard analysis system, the duration of the constant-composition section (at the column start point) that continues until the initial rise of the concentration gradient increases relative to the column capacity, and the separation of weakly retained components is affected. Therefore, in order to reduce the gradient delay in accordance with the reduction in column size, on the basis of the ratio of column capacities, select a gradient mixer with a capacity that is optimum for an ultrafast analysis system. The capacity of the gradient mixer can be calculated with the following equation.
VMF = VMC x RVF / RVC
VMF: Mixer capacity with Shim-pack XR-ODS
VMC: Mixer capacity with standard analysis column
RVF: Capacity of Shim-pack XR-ODS
RVC: Capacity of standard analysis column
For example, with a standard analysis system using a 1.7-mL gradient mixer, when reducing the column size by switching to a Shim-pack XR-ODS with a length of 75 mm and an inner diameter of 3 mm, if the delay capacity of the entire system is taken into consideration, the optimum gradient mixer capacity will be 0.1 mL, and so a semi-micro mixer will be required.