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 an electron impact (EI) MS. As for losses (or gains) of neutral fragments, subtracting a mass-to-charge peak from the molecular ion will produce a calculated neutral loss spectrum. The purpose of the calculated neutral loss spectrum is to facilitate the calculation of the losses and thus assist in fragment interpretation.
The EI mass spectrum of Bisphenol A (aka BPA – an environmentally unfriendly agent) and its calculated neutral loss spectrum are shown below. The loss of 15 (demethylation) is calculated by subtracting the molecular ion for BPA at 228 from the most intense signal at m/z 213.
Thank you to Graham McGibbon Ph.D. for suggesting the compound.