Microwave Plasma Systems in Optical and Mass Spectrometry

Abstract

AbstractOver the last decade, a revolutionary progress in both the instrumentation and the application of microwave plasma (MWP) systems for optical and mass spectrometry is observed. In this article, the current status of these systems is comprehensively reviewed and updated to 2022 to provide the reader with an advanced understanding of the theory, practices, and instrumentation associated with MWP‐based spectrometric techniques. Diverse MWP devices that can serve as atomizers, and radiation or ionization sources for various spectrometric techniques are all discussed and classified according to their fundamental microwave features and power coupling mode. Two basic MWP types constitute electrode‐operating capacitively coupled microwave plasmas (CMPs) and electrodeless microwave‐induced plasmas (MIPs). The recent development of the brand new devices such as microwave inductively coupled plasmas, rotating field MWPs, and microwave micro‐discharges is also discussed. In addition, so‐called tandem plasma sources that are a combination of MWP with another type of plasma are briefly commented on.An introduction to the various sampling techniques that can cope with MWPs such as hydride generation (HG), chemical vapor generation (CVG) and photochemical vapor generation (PCVG) for gaseous samples, solution nebulization for liquids, and dry aerosol generation techniques [electrothermal vaporization (ETV), spark (SA), laser ablation (LA), direct vaporization and ionization (DI), and continuous powder introduction (CPI)] for solids are presented highlighting their relative merits and demerits. Also, recent advances in sampling of nanoparticles for time‐resolved measurements and single particle analysis are mentioned. Further, a broad range of MWP‐based optical and mass spectrometric techniques is covered. Optical emission spectrometric (OES) methods based on MWPs are reviewed because a considerable amount of research is presently being performed in this field. Even when much less reported in the literature, several nonemission spectrometric techniques are also discussed. The mass spectrometry (MS) techniques including both the elemental mass spectrometry with hot MWPs and a variety of molecular MS techniques utilizing either hot or cold MWPs are discussed.Advances in sample introduction strategies, instrument optimization, calibration methods, and applications of MWP analytical spectrometry are discussed in the following sections. Due to the diversity of MWP instrumentation and related spectrometric techniques, it is impracticable to treat equally all of these issues in this survey. For this reason, the discussion of analytical performance and practical use is focused on key MWP‐based spectrometric techniques that have been employed, alone or hyphenated, using commercial instrumentation.The review of routine determination of metals and metalloids in different categories of samples is focused to cover the application of nitrogen MWP Optical Emission Spectrometer. Extended capabilities by hyphenating microwave plasma optical emission spectrometry (MWPOES) and microwave plasma mass spectrometry (MWPMS) to various well‐known separation techniques such as gas or liquid chromatography, and also size‐exclusion chromatography are discussed in brief.The application of advanced spectroscopic techniques in a wide range of environments focusing mainly, but not exclusively, on industrial and bioanalytical applications, its advantages, and limitations over other multielement instrumental techniques are discussed. Some of the areas where more developments can be expected in the future are suggested.