Development of an Ion Store/Time-of-Flight Mass Spectrometer for the Analysis of Volatile Compounds in Air

• Published in: Analytical chemistry (Washington) Vol. 69; no. 18; pp. 3780 - 3790
• Main Authors: Chambers, David M, Grace, Louis I, Andresen, Brian D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15-09-1997
• Subjects: Air pollution; Analytical chemistry; Chemistry; Environmental monitoring; Exact sciences and technology; Ions; Scientific imaging; Spectrometric and optical methods; Ion trap; Chemical analysis; Time of flight method; Instrumentation; Air pollution; Volatile organic compound; Air; Performance; Real time; Mass spectrometry; Monitoring
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac970102g

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 μs, thus yielding a duty cycle near 100%. The necessary hardware and electronics configuration needed to obtain optimum resolution (routinely 2000 m/Δm, fwhm), mass accuracy and sensitivity is described.