Is M+ peak the molecular weight?

Mass spectrometry measures the mass to charge ratio of molecules, gives structural information about a compound and can tell us the molecular mass of a compound. The M in M+ represents molecular mass and the + sign indicates a positive charge. Ions with the highest m/z value are the heaviest ions and are likely to be the molecular ion (M+) in the mass spectrum. The highest m/z value may also represent the molecular mass of the molecule. However, complications arise when there is a possibility of different isotopes (of carbon, chlorine, or bromine) in the molecular ion.