Time-of-flight mass spectrometry as a tool for speciation analysis

Abstract

Time-of-flight mass spectrometry (TOFMS) has recently been introduced as an alternative to scanning-based mass analyzers for use in elemental analysis. Coupled with an inductively coupled plasma or alternative ion source, TOFMS can produce a complete atomic mass spectrum in less than 50 μs. Because of this high spectral-generation rate, even very brief transient signals can be recorded with high fidelity. Furthermore, each mass spectrum is derived from the same sub-microsecond pulse of ions, so high precision can be achieved by using either isotope-ratioing or internal standardization techniques. All these features make TOFMS attractive for the measurement of transient signals, such as those commonly encountered in speciation analysis. In this paper, the capabilities of TOFMS in speciation will be demonstrated through the coupling of gas chromatography and capillary electrophoresis with an inductively coupled plasma-TOFMS. Additionally, the development of novel switched gas sampling glow discharge (GSGD) ionization sources will be described and their role in chemical speciation will be evaluated. The switched GSGD has the ability to collect both atomic and molecular mass spectra in rapid succession, to provide additional information about chemical species. The coupling of various sample introduction systems (flow-cell, exponential dilutor, capillary gas chromatography and electrothermal vaporization) to the GSGD is outlined.