Ion storage techniques and time-of-flight mass spectrometry in physical forensic science

Describes an ion storage trap/time-of-flight mass spectrometer (IS/TOE-MS) for performing real-time monitoring of volatile and semivolatile compounds in air. We selected this approach because the IS/TOF-MS combination is capable of providing both fast analysis and sample preconcentration needed for trace-air analysis. Specifically, the IS, which serves as the pulsed extraction source for the TOF-MS, can also be used to preconcentrate target chemicals to lower detection limits. TOE/MS provides for real-time monitoring whereby an entire mass spectrum typically can be produced in less than 100/spl mu/s. Given the relatively long storage-time capability of the IS (i.e., 10 ms to rather than 1 s), the IS/TOF-MS system achieves a duty cycle that approaches 100%. The transmission efficiency in the IS/TOF-MS is equally as high because the entire ion population accumulated in the IS device can be extracted toward the TOF/MS. The theory and operation of the IS as a pulsed extraction source for TOF-MS analysis of VOCs is discussed and the instrument's performance is evaluated.