How to find the molecular and fragmented molecular ions in the mass spectrum?

Question

1. Can anyone teach me how to find the molecular and fragmented molecular ions in the mass spectrum?

2. The nitrogen trichloride molecule consists of three isotopes, N-14, Cl-35 and Cl-37. What are the molecular and fragmented molecular ions of nitrogen trichloride?

Thanks for answering my question.

Answer 1

The molecular ion is going to correspond to the total mass of the unfragments part e.g. the mass of nitrogen trichloride and is going to the the highest mass peak on the spectrum.  The fragement peaks are going to be ions that have had one or more of the chlorines fragmented off.  If I remember correctly (been a while since I had to recall my mass spec teachings) the other isotopes will appear next to the main fragment peak and according to the ratio of the isotope to the normal element; if you know this ration it helps in making the assignment of the peak to a particular fragment; e.g if you have a strong peak, and 2 mass unit up there's a peak with about 1/4 of the intensity of the main peak it is going to tell you that the main peak contains chlorine as the second peak is the same fragment but containing Cl-37 instead of Cl-35.