Fig. 6. Katritsky pyrylium reaction performed online using paper spray ionization mass spectrometry. Different reaction rates are indicated by different mass spectrometric signal intensities of product and reactant. Left top: General reaction scheme depicting the Katritsky reaction. Right top: Comparison of the reaction rates in bulk solution vs. reaction in droplets arising from paper spray ionization. Left bottom: Intercharge distance effects. Right bottom: Substituents effects.⁶⁶⁾.