Liquid Chromatography - The Mobile Phase Supply System 2
Figure 2. The High Pressure Gradient Programmer
Solvent passes from each reservoir directly to a pump and then to a mixing manifold from which it passes to the sample valve and column. The pumps control the actual program and are usually driven by stepping motors. The volume delivery of each solvent is controlled by the speed of the respective pump which is precisely determined by the frequency of its power supply. The controlling frequency can be generated either by external oscillators or, if the chromatograph is computer controlled, directly from the computer itself.