In a typical mass spectrum, a smaller signal is observed at a mass 1 amu higher than the molecular ion peak. Why

Answer is explained below in the explanation section

Explanation:

Smaller signal is observed at a mass 1 amu because small percentage of the compound will have carbon isotope of 13C instead of 12C.

As we know, mass spectrometry is done as a small compound is first vaporized and then bombarded to ionize it. And then, those ions are accelerated forward and then at some point ions are separated and deflected by the application of magnetic field.

And finally hits the detector to give us a spectrum to read. So, in this whole procedure, there can be a small percentage of carbon isotope of 13C instead of 12C in that compound and showed in the spectrum as a smaller signal at a mass 1 amu.