Method and system for providing a modifier to a curtain gas for a differential mobility spectrometer

A method of operating a system including a differential mobility spectrometer, the method comprising:

• a) creating ions in an ion source and transporting the ions from the ion source to an inlet of the differential mobility spectrometer, the inlet being disposed downstream from the ion source;
• b) providing a boundary member that surrounds the differential mobility spectrometer so as to define a curtain chamber, an inlet of the differential mobility spectrometer opening up into the curtain chamber, the outlet of the differential mobility spectrometer being configured so as to allow the ions to exit the curtain chamber;
• c) providing a curtain gas supply that provides a curtain gas at substantially atmospheric pressure, the curtain gas supply comprising a curtain gas conduit;
• d) providing a modifier supply that provides a modifier liquid, the modifier supply comprising a modifier conduit;
• e) providing a junction for merging the modifier conduit into the curtain gas conduit;
• the curtain gas conduit being fluidly connected downstream of the junction to the curtain chamber;
• f) heating the modifier liquid and the curtain gas in the curtain chamber;
• g) directing at least a portion of the curtain gas to the inlet of the differential mobility spectrometer so as to become a drift gas
• h) adjusting a meter to define a selected volumetric flow rate for supplying a modifier liquid to the curtain gas;
• and,
• i) supplying an actual volumetric flow rate of the modifier liquid continuously to the curtain gas over a selected time interval of an analysis, wherein the actual volumetric flow rate that enters the curtain gas over the selected time interval is within a precision of about 2 percent of the selected volumetric flow rate and the concentration of said modifier liquid in said curtain gas is at least 1%.