ACD/Labs Blog

Without correctly identifying the molecular ion on a mass spectrum, the nitrogen rule generally cannot be applied to any arbitrary ion peak. The chemical structure for N-[(1E)-1-phenylethylidene]methanamine and its EI mass spectrum are shown below. As expected, the odd value for the molecular ion at m/z 133 dictates an odd number of nitrogen atoms. However,...

For MS data, the ionization method will dictate how the nitrogen rule is applied. For example, if the ionizer is Electron Impact (EI) ionization, then the nitrogen rule is to be applied to the molecular ion [M]+* as follows: -an odd nominal mass indicates an odd number of nitrogen atoms, e.g. 1,3,5 -an even nominal...

The purpose of the nitrogen rule is to assist with deciphering how many nitrogen atoms are present without any prior information on the molecular formula. Depending on the ionization mode, an odd nominal mass indicates an odd number of nitrogen atoms, e.g. 1,3,5, whereas an even nominal mass indicates an even number of nitrogen atoms,...

A calculated neutral loss spectrum is obtained from a mass spectrum by determining the mass differences between the precursor ion m/z and each of the other peaks in the spectrum and plotting the original intensity versus neutral mass. Neutral losses with small masses have limited possibilities for their composition and thus can facilitate the identification...

As a first pass, a good approach to extracting information from a mass spectrum (MS) is to look for two things: intense peaks with a recognizable m/z and losses (or gains) between peaks. A mass-to-charge peak at 77 is an example of a recognizable peak; it is most likely attributed to a C6H5+’ fragment in...