Syringe Pumps Liquid chromatography, as originally invented by Tswett used columns packed with fairly large particles and, thus, the flow of the liquid mobile phase through the bed could be achieved by gravity pressure. Early in the 1940s, Martin suggested that the highest efficiencies from a packed column would be obtained from the use of very small particles. However, when the small particles were eventually used in the 196 0s the flow impedance was dramatically increased and, thus, required the mobile phase to be delivered at high pressures. The first pumps to be used were syringe pumps which were, in effect, large stainless steel motor driven hypodermic syringes. They provided a very constant flow rate which was virtually pulseless, but required a rather frequent, lengthy and involved refilling process. In addition unless some form of marine engineering was employed, the pumps could not operate at very high pressures. Due to these disadvantages the syringe pump was soon replaced by piston pumps which, although far from being pulseless, were much easier to operate. Today, syringe pumps are rarely used in mobile phase supplies but they are still used very effectively in both pre-column and post-column reactors. Their very constant flow rate provides accurate reagent addition and in post-column reactors does not introduce detector noise.