The different components in the mixture pass through the column at different rates due to differences in their partitioning behavior between the mobile liquid phase and the stationary phase.
Solvents must be degassed to eliminate formation of bubbles. The pumps provide a steady high pressure with no pulsating, and can be programmed to vary the composition of the solvent during the course of the separation.
The liquid sample is introduced into a sample loop of an injector with a syringe. When the loop is filled, the injector can be inject the sample into the stream by placing the sample loop in line with the mobile phase tubing.
The presence of analytes in the column effluent is recorded by detecting a change in refractive index, UV-VIS absorption at a set wavelength, fluorescence after excitation with a suitable wavelength, or electrochemical response. Mass spectrometers can also be interfaced with liquid chromatography to provide structural information and help identify the separated analytes.
Schematic of an HPLC instrument
Picture of an HPLC instrument