Stopped-flow mass spectrometry with rotating ball inlet : Application to the ketone-sulfite reaction

A new device for continuous introduction of aqueous sample into a mass spectrometer, the rotating ball inlet, was used in the construction of a stopped-flow mass spectrometer. The rotating ball drags sample adhering to its surface past a polymer gasket into the vacuum of the mass spectrometer, where it evaporates and is ionized by electron impact. When the rotation of the ball is turned on or off, the mass spectrometric signal of an organic volatile solute responds with a half-time of 0.1 s, indicating the intrinsic response time of the mass spectrometer. There are no other significant contributions to the response time, and concentration transients with half-times down to 1 s can be recorded. Utilizing a flow cell version of the rotating ball inlet in conjunction with a stopped-flow device, we have studied the reactions of acetone and butanone with S(IV) species by recording transients in the concentrations of the ketones. Pseudo-first-order rate constants were determined at varying pH values. Second-ord...