| Time-of-flight mass spectrometry (TOFMS) has emerged as a powerful tool for the analysis of biological, organic, and inorganic samples. The trade-off between precision and sensitivity is not required when TOFMS is employed because all ions in the beam are sampled at the same instant in time, thus a complete mass spectrum is generated for each event and all m/z's are detected essentially simultaneously. Moreover, the TOF is ideally suited for interfacing with sources that produce transient signals since this spectrometer is designed to sample discrete ion packets.;We recently have developed a novel ionization source, the gas sampling glow discharge (GSGD), that has been interfaced to an orthogonal extraction TOFMS. The helium GSGD is a versatile device that can generate both atomic and molecular fragment patterns for a sample vapor. In most cases, the molecular fragmentation patterns strongly resemble conventional 70 eV electron impact mass spectra. More importantly however, it is possible to rapidly (>100 Hz) switch the source between hard and soft ionization modes; information from each spectrum can be collected sequentially with a boxcar integrator. A variety of sample introduction systems have been coupled with the GSGD, including a flow-cell, exponential dilutor, capillary gas chromatograph, and electrothermal vaporizer. The advantages of producing both types of mass spectra in a single analytical sequence are immediately apparent and this capability can be applied profitably to chemical speciation studies.;We have also developed a hexapole collision cell for the inductively coupled plasma TOFMS and used it to improve instrumental figures of merit. The sampled ion beam possesses a velocity component that lies perpendicular to the TOF axis, which leads to a mass-dependent steering plate bias and is a disadvantage particular to the right-angle geometry. The sampled ions are collisionally dampened and focused within the hexapole; the resulting beam is nearly mono-energetic and the steering plate bias removed. Furthermore, the kinetic energy distribution of the argon ion beam is reduced through collisions with buffer gas and mass resolution is improved. The collision cell can be used to effect selective and specific ion-molecule reactions that might serve to mitigate spectroscopic interferants. In the present study, charge exchange with hydrogen buffer gas lowers the quantity of argon ions transferred into the TOF extraction zone which in turn reduces chemical noise, eliminates the need for a deflection pulse, and removes calcium and iron isobars. |
