Mobile phase holds the solvent. A high-pressure pump is used to generate and meter a specified flow rate of mobile phase. An injector (Autosampler) is able to inject the sample into the continuously flowing mobile phase stream that carries the sample into the HPLC column. The column contains the chromatographic packing material needed to effect the separation. This packing material is called the stationary phase because it is held in place by the column hardware. A detector (Refractive Index) is needed to see the separated compound bands as they elute from the HPLC. The mobile phase exits the detector and can be sent to waste, or collected. When the mobile phase contains a separated compound band, HPLC provides the ability to collect this fraction of the eluate containing that purified compound for further study.
The detector is wired to the computer data station, the HPLC system component that records the electrical signal needed to generate the chromatogram on its display and to identify and quantitate the concentration of the sample constituents. Since sample compound characteristics can be very different, several types of detectors have been developed.