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Mass spectrometry (MS) is an analytical method that first ionizes a substance, separates the ions according to their mass-to-charge ratio, and then measures the intensity of various ion peaks to achieve the analytical purpose. Different types of mass spectrometers use electric or magnetic fields to manipulate ion motion and determine their mass-to-charge ratios.
The basic components of a mass spectrometer are the ion source, mass analyzer, detector, and data and vacuum systems. The ion source is where the sample components introduced into the MS system are ionized using an electron beam, photon beam (UV light), laser beam, or corona discharge. In the case of electrospray ionization, the ion source transfers ions present in a liquid solution to the gas phase, transforming and splitting neutral sample molecules into gas-phase ions, which are then sent to the mass analyzer. When the mass analyzer classifies ions based on their mass by applying electric and magnetic fields, the detector measures and amplifies the ion current to calculate the abundance of each mass-separated ion. A bar graph with the ion signal intensity detected by the detector as the vertical axis and the ion mass-to-charge ratio as the horizontal axis is the commonly seen mass spectrum.
Its main terms include: Mass-to-charge ratio: The ratio of the ion's mass (in relative atomic mass units) to its charge (in units of electron charge), written as m/Z; Peak: The ion signal in the mass spectrum is usually referred to as the ion peak or simply peak; Ion abundance: The ion signal intensity detected by the detector; Base peak: In a mass spectrum, the ion peak with relatively high intensity within a specified mass-to-charge ratio range is called the base peak.
LC-MS, short for Liquid Chromatography-Mass Spectrometry, is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography (or high-performance liquid chromatography) with the mass analysis capabilities of mass spectrometry (MS). Liquid chromatography technology separates mixtures with multiple components, while mass spectrometry technology is responsible for detecting and analyzing the structural characteristics of various components with high molecular specificity and detection sensitivity. These two technologies achieve synergistic enhancement. It belongs to the category of chromatographic-mass spectrometry combined techniques alongside gas chromatography-mass spectrometry (GC-MS). It is suitable for protein mass spectrometry identification, protein quantitative proteomics, protein post-translational modification identification, and protein interaction validation, widely applied in biotechnology, environmental monitoring, food processing, pharmaceutical, and other fields.
Liquid Chromatography-Mass Spectrometry (LC-MS) operates at room temperature and is mainly used for the analysis and measurement of non-volatile compounds, polar compounds, thermally unstable compounds, and large molecular weight compounds (proteins, peptides, polymers, etc.). Its analytical data currently lacks commercial databases for comparison; data can only be analyzed by building databases or interpreting spectra manually. In contrast, Gas Chromatography-Mass Spectrometry (GC-MS) operates at elevated temperatures and is mainly suitable for the analysis and measurement of volatile compounds, thermally stable compounds, small molecular weight compounds, and gasifiable compounds; spectra are obtained using electron impact (EI) and can be compared with standard libraries. GC-MS is an earlier commercialized coupling instrument, but its narrow applicability range limits its use to some extent, with statistics indicating that only about 20% of organic compounds can be analyzed by gas chromatography.
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