A low pressure gradient system consists of one pump with an integrated mixing block that enables the delivery of up to four different solvents at the same time. Mixing takes place on the low pressure side of the pump and a single pump is operated at a constant flow rate.
High pressure gradient systems are composed of two pumps. These systems are limited to two solvents which are pumped by the separate pumps. The mixer is located on the high pressure side of the pump. The mobile phase mixture is controlled by the relative flow rate of the two pumps. The flow rate is determined by the combined flow rate of both pumps.