The HPLC is used to separate a sample mixture into its different components on a chromatography column. The column is packed with a 'stationary phase', made of small particles with certain surface chemistry. The sample to be analyzed is injected in a small volume into the stream of solvent ( the 'mobile phase') that is pumped at high pressure through the column.
Different compounds, injected as a mixture into the HPLC column, partition differently between mobile phase and stationary phase and take different times to cross the column and reach the detector, where their presence is recorded and their concentration is measured. Different 'retention times' reflect the affinities of the different compounds for the stationary phase of the column, relative to the mobile phase. A Compound with a lower affinity for the stationary phase, has a shorter retention time and is plotted closer to the origin of the chromatogram.
The Agilent 1200 HPLC system, includes several modules: