Schematic of DART ionization process

When the DART ion sonrce is placed near the opening to the mass spectrometer, the ions are sacked in by vacnnm. 

The sample to be analyzed is introduced into a stream of mobile phase. The analyte molecnles are swept through the column by the mobile phase and retarded by specific chemical or physical interactions with the stationary phase. The amount of retardation depends on the nature of the analyte, stationary phase, and mobile phase composition. The time for a specific analyte to traverse the length of the column is called the retention time. Various stationary phase materials result in predictable interactions with specific chemical families, thns giving the desired degree of 

The choice of solvents and gradient depend on the nature of the stationary phase and the analyte. Often, a series of tests is performed on the analyte, and a number of trial runs may be processed to find the HPLC method that gives the best separation of components. 

The combination of HPLC and mass spectrometry was impossible for many years due to the difficulty in removing the solvent prior to the analyte entering the high vacuum of the mass spectrometer. However, with the advent of the atmospheric pressure ionization techniques discussed previously, the two instruments have been combined to give the relatively new technique of LCMS. The eluant from the HPLC is passed into one of the atmospheric pressure ion sources, where ions are produced and most of the solvent is rapidly evaporated. The ion cloud then passes through a small aperture into the vacuum of the mass spectrometer, where the solvent is totally removed, and the ions can be focused and mass analyzed in the normal manner. 

Some limitations to the normal array of HPLC methodologies exist for LCMS applications  

---