What process is most often used in LC-MS to introduce the sample into the mass filter?

Electrospray ionization (ESI) is the most commonly used method for introducing samples into the mass filter in liquid chromatography-mass spectrometry (LC-MS). This technique allows for the effective transfer of analytes from the liquid phase to the gas phase while preserving their ionic states, which is crucial for accurate mass analysis.

In ESI, a high voltage is applied to a liquid passing through a narrow capillary, creating a fine mist of charged droplets. As the solvent evaporates from these droplets, the charge density increases, eventually resulting in the emission of ions into the gas phase. This process is particularly advantageous for analyzing large biomolecules, such as proteins and peptides, due to its ability to maintain their structural integrity and provide high sensitivity.

While other ionization techniques like chemical ionization, electron impact ionization, and fast atom bombardment are valuable in various applications within mass spectrometry, they are not as routinely employed in LC-MS for sample introduction. For instance, chemical ionization typically requires the analyte to be vaporized and not well-suited for directly handling aqueous samples. Electron impact ionization is more effective for small, volatile compounds and operates under vacuum conditions, while fast atom bombardment is often used for larger, thermally lab