Real-Time Monitoring of Reactions by Headspace Sampling under Ambient Mass Spectrometric Conditions

The helium-plasma (HePI) ionization mass spectrometry method was used to track the formation of reaction products and consumption of reactants by continually monitoring the vapors in the reaction headspace in real time. Two examples of the application procedure are presented here: a nucleophilic acyl substitution reaction and a 1,4-nucleophilic addition process. For the purposes of the work, a specially constructed helium-plasma ionization (HePI) source was mounted on a single-quadrupole benchtop mass spectrometer. However, any electrospray source is easily convertible to an ambient HePI source. This setup has the potential to be used in the teaching of organic and analytical chemistry laboratories, as well as for demonstrations. Because the procedure requires only the headspace of the reaction vessel to be sampled by an easily prepared Venturi suction device (pump), the experiments can be quickly set up and adapted for any available mass spectrometer equipped with an electrospray source. For sampling, students can be shown how to prepare their own Venturi pumps and conduct reactions at different temperatures.