A GPC system consists of various instruments. Injectors are used to introduce the polymer solution into the columns of separation. Pumps deliver the sample and solvent through the columns and the system. Detectors record the exit of fractions of the sample and count the number of molecules of a certain MW. The computer controls the test automatically, records the results, and calculates the different MW averages. The GPC system contains a number of different instruments that work together to provide the optimum system performance. Figure 17.3 shows a schematic of a gel permeation chromatograph with the basic components.