Development of an ion store time-of-flight mass spectrometer for the analysis of volatile compounds in air

A time-of-flight mass spectrometer (TOF-MS) that incorporates an ion storage trap as a pulsed extraction source and sample preconcentrator has been developed for air monitoring, This new instrument configuration is designed for real-time monitoring of changes in trace volatile and semivolatile compound concentrations in air. Typically, detection limits are in the low parts per billion (v/v) range. This ion store/TOF-MS configuration permits. a relatively large volume air flux to be drawn directly into the ion trap cavity, creating a local pressure that exceeds 10(-4) Torr. Operating the ion trap at this pressure increases the extent of chemical ionization with the abundant N2- and O2+ that are formed by electron impact The air background also serves as a suitable collisional damping matrix, helping to compress the ion cloud to the center of the trap, which is ideal for TOF-MS analysis. Ions are typically accumulated in the trap for 400 ms, at which point they are extracted through the exit end cap and analyzed within 100 ps, thus yielding a duty cycle near 100%. The necessary hardware and electronics configuration needed to obtain optimum resolution (routinely 2000 m/Delta m, fwhm), mass accuracy and sensitivity is described.