Relation between charge state distributions of peptide anions and pH changes in the electrospray plume. A mass spectrometry and optical spectroscopy investigation

Abstract A laser-induced fluorescence set-up profiling physico-chemical parameters of droplets and their changes in an electrospray plume is coupled to an Agilent single quadrupole mass spectrometer equipped with an Agilent Jet Stream electrospray source. This coupling allows investigating the evolution of the pH of droplets as they evaporate in the electrospray plume by measuring emission spectra of a pH-chromic dye. Simultaneous measurement of mass spectra and optical pH profiling permits to study the relation between the charge states of peptide anions in mass spectra and pH changes in the spray plume. In particular, due to changes in droplets evaporation rates, the source parameters (i.e., sheath gas flow and temperature) influence the pH of the droplets and relative intensities of charge states in peptide mass spectra.