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.