Reaction cells and collision cells for ICP-MS: a tutorial review

This paper reviews the literature published to September 2001 relating to the history, design, operation and application of linear radio-frequency (r.f.)-driven multipole collision cells and reaction cells in combination with inductively coupled plasma mass spectrometry. The available material is supplemented with original experimental data that demonstrates the principles presented. The relation of these devices to collision cells for organic mass spectrometry and to the three-dimensional ion trap is discussed in its historical context. A general tutorial on the fundamentals of ion collision and reaction, including thermochemistry, energy transfer and reaction kinetics, is given. Consideration is given to some of the fundamental aspects of operation and design of linear r.f. devices. This historical and fundamental framework then allows the tutorial to focus on the promotion and control of ion–molecule chemistry in linear r.f.-multipole cells for elemental analysis. Vacuum requirements are considered in some detail, and deal in particular with the issue of contamination of the reaction gas. Special attention is paid to the thermal characteristics of the ions in the cell, as this has important implications for the application of the available databases of thermochemical and thermal kinetic data to the development of analytical methods. Calculation and experimental validation of the efficiency of the ion–molecule chemistry leads to the recognition that secondary, sequential chemistry can play a limiting role in the realization of the potential of the cell method. The two principal means of controlling the analytical impact of the secondary chemistry, through post-cell kinetic energy discrimination and through in-cell mass-bandpassing are discussed and contrasted through spectral data acquired for different reaction gas types and pressures. The available literature on the application of collision cells and reaction cells for the analysis of samples of high purity, environmental, geological and biological materials is critically reviewed.