Chemical Ionization Mass Spectrometry: Fundamental Principles, Diverse Applications, and the Latest Technological Frontiers

The review examines the evolution of chemical ionization mass spectrometry (CI-MS), a technique developed in 1966 by Field and Munson. CI is a soft-ionization method that produces more intense molecular ions with less fragmentation than electron ionization (EI). CI-MS is widely utilized across various fields, including atmospheric chemistry, environmental science, and biomedical research. The article highlights different CI-MS types, such as proton transfer reaction mass spectrometry (PTR-MS), which is renowned for its ability to analyze volatile organic compounds in real-time; negative ion CI-MS, which provides insights into anions; selected ion flow tube mass spectrometry (SIFT-MS), and ion-drift chemical ionization mass spectrometry (ID-CIMS), techniques that allow for the direct analysis of trace gases with high sensitivity and specificity. The article discusses advancements in chromatography with CI-MS, particularly atmospheric pressure chemical ionization (APCI) and liquid electron ionization (LEI) interface. The ongoing exchange of data between fundamental ion/molecule studies and specific applications has significantly boosted the growth of CI-MS in recent decades. In recent years, no extensive review has been published on CI-MS. This article provides an overview of CI-MS technique, its applications, and its evolution over the years, highlighting its importance in advancing scientific research and understanding the chemistry of various environments.