Quantitative Perspective on Online Flow Reaction Profiling Using a Miniature Mass Spectrometer

Online mass spectrometry has proven to be a useful tool for characterizing many aspects of chemical reactions. However, to the best of the authors' knowledge, no reference standard (RS) quantitation approach has been applied in online MS profiling work to date. In this study, we present a RS approach for online quantitation of an aerobic oxidation reaction in flow using a miniature mass spectrometer, with both internal RS and external RS quantitation approaches being evaluated. Quinoline, a structurally similar and chemically inert compound under these reaction conditions, was chosen as the RS to quantify the pyridine aldehyde product. To investigate the optimal RS concentration and instrument attenuation, calibration curves were established by plotting the product/RS peak intensity ratio against the theoretical product yield at different attenuation (dilution factor) values. The MS quantitation results for the actual flow reactions were validated with conventional offline H-1 NMR analysis.