A @[email protected] reaction may be written: \[\text{M}_{1}^{+}\rightarrow \text{M}_{2}^{+}+\text{M}_{3}\] The @[email protected] of a @[email protected] ion of mass-to-charge ratio \(\frac{m_{1}}{z_{1}}\) into an ion of mass-to-charge ratio \(\frac{m_{2}}{z_{2}}\) after electric @[email protected] of the @[email protected] ion and before magnetic deflection gives rise to a peak in the @[email protected] at an apparent mass, \(\frac{m_{2}^{2}\ z_{1}}{m_{1}\ z_{2}^{2}}\). The symbol \(m^{*}\) should be used to indicate the apparent mass of the product ions giving rise to this peak. Traditionally, the peak itself has been called a @[email protected] peak and this should preferably be expressed as @[email protected] peak. It is nevertheless recommended that the former term should be retained. The word @[email protected] should never be used as a noun. Its use as an adjective should be limited to such terms as @[email protected] ion, where it is used correctly, and to the special case of @[email protected] peak discussed above. It should never be used in such terms as @[email protected] reaction, @[email protected] @[email protected], @[email protected] studies, etc. It should be clear that the @[email protected] ion is the ion that undergoes @[email protected]; it is not detected. When a reaction is written with an asterisk above the arrow as shown: \[\text{M}_{1}^{+}\overset{\text{*}}{\rightarrow }\text{M}_{2}^{+}+\text{M}_{3}\] this means that the reaction has been confirmed by the observation of a @[email protected] peak. The textual description of such a process may be written as, for example, (\(m^{*}\), \(43\rightarrow 28\), calcd. 18.2, obsd. 18.3) meaning 'for the @[email protected] \(\frac{m}{z}\ 43\rightarrow \frac{m}{z}\ 28\) a @[email protected] peak at \(\frac{m}{z}\) 18.3 (calculated 18.2) has been observed'.