Mass Spectrometry Determining the molecular formula of an unknown compound Model 1: Mass Spectrum of Acetone Questions 1. Label the peak due to the "molecular ion" of acetone with [M] (symbol for a molecular ion). 2. What is the peak intensity (relative height) of the [M]+peak in this spectrum? 3. What is the weight (m/z) and intensity (height) of the most common ion detected during this mass spectrometry experiment? (This will be the tallest peak on the mass spectrum.) Label this peak as the base peak. WARNING! The [M]+peak (molecular ion) is often NOT the same as the base peak (largest peak). The base peak is easy to identify since it is always the larges peak (by convention set to 100). 4. a. What is the size (in amu) of the neutral fragment that was lost to give the ion responsible for the base peak at m/z=43 ? b. What combination of atoms weighs the amount you reported above, and whose loss could account for the peak at m/z=43 ? The major peaks on a mass spectrum representing ions lighter than the molecular ion are called fragment peaks. Draw an ion that could account for the m/z=43 peak