Basic Principles of Mass Spectrometry

Mass spectrometry (MS) is a spectroscopic method in which the sample to be analysed is first ionised, and then analysed by measuring its mass-to-charge ratio. The detailed analytical process is as follows:

(1) The target substance is ionised via various ionisation methods (such as electron bombardment) to produce charged molecular ions or ion fragments:

(2) The molecular ions or fragment ions of the target are guided along a specific transfer path into the mass analyser;

(3) Upon exiting the mass analyser, the detector collects and records the ions in a specific order based on their mass-to-charge ratio, thereby generating a mass spectrum [1–3].

Mass spectrometry is essentially a form of chemical analysis; it is a spectroscopic analytical method on a par with wave spectroscopy and optical spectroscopy. By analysing mass spectrometry peaks at different positions, the molecular weights of different substances can be determined; alternatively, by analysing fragment peaks, the chemical structures of different substances can be identified. Furthermore, by integrating the mass spectrometry peaks, quantitative analysis can be performed. Consequently, mass spectrometry can be utilised in numerous applications, including the determination of relative molecular masses, the identification of chemical structures, isotope analysis and the identification of isomers.

Today, with the rapid development of disciplines such as computer science, mechanical automation and physics, mass spectrometry has entered a new era, advancing towards high-throughput, high-sensitivity, high-resolution and miniaturised, portable systems. Mass spectrometry has now firmly established itself as a chemical analytical method capable of analysing complex samples, whether inorganic or organic. Owing to its high sensitivity, strong specificity, high resolution, minimal sample requirements and rapid analysis speed, mass spectrometry is attracting increasing attention from researchers and is being applied in many fields, such as environmental protection [41], food safety [51], materials testing [ljl6], life sciences [71], clinical medicine [8] and aerospace [9]. Whilst mass spectrometry supports these fields, the development of these sectors in turn drives the continuous innovation and advancement of the technology.

The origins of mass spectrometry can be traced back to the late nineteenth century, when scientists E. Goldstein and W. Wein independently observed, during low-pressure discharge experiments, that positively charged particles from the anode and other positively charged particles could be deflected in a magnetic field; it was these findings that laid the groundwork for the development of mass spectrometers. The world’s **first** mass spectrometer was successfully developed by the British scientist Joseph John Thomson in 1919. Early mass spectrometers were primarily used in the field of inorganic chemistry, for the determination of isotopes, non-radioactive elements and nuclides. In the early to mid-20th century, as mass spectrometry technology developed further, it gradually became an important method of chemical analysis and was adopted by many chemists. From the 1940s onwards, with the outbreak and progression of the Second World War, mass spectrometry began to be widely applied in key wartime sectors such as the petroleum and chemical industries; it was only then that the technology gradually found its way into the field of organic analysis. In 1966, three scientists—M.S.B., F.H. Field and Munson—used chemical ionisation (CI) [10] to detect biomacromolecules for the **first time**. Subsequently, with the advent of ‘soft ionisation’ techniques such as electrospray ionisation (ESI) [11] and matrix-assisted laser desorption/ionisation (MALDI) [12], mass spectrometry began to be widely applied in cutting-edge fields such as the life sciences and clinical medicine. In the more than 100 years since the advent of mass spectrometry, its importance across numerous fields has become self-evident as the technology has evolved. According to incomplete statistics, mass spectrometry and related methods have, to date, led to several Nobel Prizes in fields such as physics and chemistry; Table 1.1 provides a summary of the Nobel Prizes awarded for the use of mass spectrometry and related methods.