Quantitative online analysis of liquid-phase products of methanol oxidation in aqueous sulfuric acid solutions using electrospray ionization mass spectrometry.

We describe a novel method and setup for quantitative online analysis of the liquid-phase methanol oxidation products in acidic aqueous solutions by electrospray ionization mass spectrometry (ESI-MS). This includes a specially designed flow system, which allows continuous online mixing, derivatization, extraction, separation, and quantitative detection within ca. 3 min. For electrospray ionization of formaldehyde, it is first online-derivatized by 2,4-dinitrophenyl hydrazine to form the easily ionizable 2,4-dinitrophenyl hydrazone. Then, both formic acid and derivatized formaldehyde are online extracted into an immiscible organic phase, which, after separation from the aqueous phase, is piped to the ESI-MS for analysis. This strategy ensures complete removal of the highly corrosive sulfuric acid from the analyte and allows the liquid-phase methanol oxidation reaction (MOR) products (formaldehyde and formic acid) to be quantitatively detected by ESI-MS. Finally, the potential of this method for online analysis in electroanalysis and electrocatalysis is discussed.