ionization type chemical ionization The formation of a new ion by the reaction of a neutral species with an ion. The process may involve transfer of an electron, a proton or other charged species between the reactants. When a positive ion results from chemical ionization the term may be used without qualification. When a negative ion results the term negative ion chemical ionization should be used. Note that this term is not synonymous with chemi-ionization. CI MS:1000071 MS