Electrospray droplet manipulation via reagent vapor introduction

A technique was developed to manipulate electrospray generated charged droplets via reactions with volatile reagents introduced into the interface of a QqTOF tandem mass spectrometer. This near atmospheric pressure region just outside and between the curtain and orifice plates is where the molecule/droplet interaction takes place on the sub-millisecond time-scale of the droplet evaporation. Work was devoted to exploring, developing, and optimizing this approach for a variety of applications. It was found that the introduction of volatile acids into the mass spectrometer interface can be used to remove unwanted metal counter-ions. Weak acids were best to use in the negative polarity and strong acids were best to remove metal counter-ions in the positive polarity. When proteins were ionized in the positive polarity and various acids of increasing strength were introduced, a much higher charge state distribution and average charge state were observed. Similarly, introducing bases of increasing strength in the negative polarity resulted in the observation of much higher, more negative charge states. In both cases, this was correlated to protein unfolding. Similarly, it was found that introducing acidic vapors in the negative polarity and basic vapors in the positive polarity can shift the distribution to much lower charge states, suggesting that the protein was now in a more folded conformation. To test the theory that the observed charge state distributions can be correlated to various protein conformations, hydrogen/deuterium exchange was performed using the vapor introduction technique. Deuterated acids and bases were introduced to shift the charge state distributions while at the same time performing hydrogen/deuterium exchange on the newly formed conformations. A greater degree of deuterium uptake is observed for a more unfolded conformation. Finally, various mixtures were studied to see if the vapor introduction technique can be utilized as a tool to simplify spectral analysis and eliminate common matrix effects. It was found that the introduction of volatile acids and bases effectively changes the droplet pH and will affect which components of a mixture are observed over others. The introduction of various organic solvents and the use of other carrier gases, like carbon dioxide, can also be used to affect partitioning within the droplet. In general, this is a very simple and flexible technique with many variables that can be altered to manipulate electrospray generated droplets