Hydrogen/deuterium exchange of electrosprayed ions in the atmospheric interface of a commercial triple–quadrupole mass spectrometer

Abstract

A novel H/D exchange technique capable of the deuteration of electrosprayed ions has been developed. H/D exchange was carried out by introducing deuterating agent (e.g., d-MeOH) into the curtain gas flow of a commercial triple quadrupole mass spectrometer. In contrast to the widely used H/D exchange techniques, the ions are not trapped in this case. The main advantages of this technique are the ease of use and applicability on most commercial mass spectrometers, including quadrupole-type instruments. Effect of various instrumental parameters was investigated in detail, including spray voltage, spray position, partial pressure of the deuterating agent in the curtain gas, gas flow rates, the orifice-to-skimmer potential and the source temperature. Among these only the partial pressure of the deuterating agent in curtain gas, orifice-to-skimmer potential and source temperature influenced the efficiency of H/D exchange. These suggest that the H/D exchange is likely to occur in the fore-vacuum region of the atmospheric interface. Analytical capabilities of the technique were demonstrated by differentiation of lysine and glutamine protonated molecular ions. Selective quantitation of lysine and glutamine mixtures was achieved, with a lower limit of detection of 1.5% for glutamine and 0.2% for lysine. H/D exchange of multiply charged macromolecular ions can also be carried out using this technique, which was demonstrated using cytochrome c.