New Microwave Plasmas Used for Atomic Emission Spectrometry: Applications and Opportunities.

Microwave energy is a convenient method of plasma generation, and it has long been utilized for both atomic emission spectrometry and atomic mass spectrometry. The benefits of this power source are significant; microwave energy is simple to use, inexpensive, adaptable to different waveform and application, and commercially available at low cost. Recently, researchers have created novel plasma structures based on emerging microwave technology, and started to study how microwave energy can be used to modify the conditions of plasmas of other forms and functions, with the aim of creating a new generation of excitation and ionization sources for analytical atomic spectrometry. This presentation will review several new types of microwave plasmas that may replace the conventional argon inductively-coupled plasma in atomic spectrometry. In some examples, novel technical ceramic materials are used to generate resonator structures that focus microwave fields to sustain plasmas in ambient air conditions for use in atomic emission or mass spectrometry, obviating the need for argon plasma gas. Other microwave structures are discussed which can create ultra-low power miniaturized plasma sources for specific applications, such as in the detection of chromatographic eluents in gas chromatography. Several microwave-coupling strategies will be reviewed which use focused microwave electric or magnetic fields to couple to more conventional plasmas, so as to change their plasma characteristics and improve performance for analytical measurements. The coupling of microwave energy to laser-induced breakdown spectroscopy experiments, for example, is a strategy by which the plasma conditions and lifetime of the measurement can be altered by judicious use of the microwave energy source in addition to the laser plasma itself. Analytical figures of merit and overall performance of these systems will be discussed.