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The art and science of microwave plasma (MWP) optical and mass spectroscopy is briefly presented including very recent advances in the field up to 2011. The use of MWPs as radiation sources for optical emission spectroscopy (OES) and atomic fluorescence spectroscopy (AFS) and as atom reservoirs for atomic absorption spectroscopy (AAS), cavity ringdown spectroscopy (CRDS), and laser‐enhanced ionization spectroscopy (LEIS) as well as ion sources for mass spectrometry (MS) is treated. Devices for producing both E‐type capacitively coupled microwave plasma (CMP)‐electrode and microwave‐induced plasma (MIP)‐electrodeless MWPs, including inductively coupled plasma (ICP)‐like H‐type plasmas, are classified and discussed, in addition to methods of their diagnostics, and results for the analytically relevant plasma parameters are presented. The means of generation of symmetrical plasmas and uses of microplasma devices are also presented with an effort to comment on general classification of microwave (MW) cavities. Further, the use of MWs for boosting of glow discharges (GDs) is treated along with other tandem sources. Methods for the introduction of gaseous, liquid, and solid samples into the MWP are discussed. They include direct vapor sampling (DVS), chemical vapor generation (CVG), and hydride generation (HG) techniques; dry aerosol generation techniques (electrothermal vaporization (ETV); spark ablation (SA); laser ablation (LA); and continuous powder introduction (CPI) as well as wet aerosol generation techniques using both solution and slurry nebulization. Special reference is made to coupling with gas chromatography (GC) and also with various separation techniques for liquids including high‐performance liquid chromatography (HPLC). The analytical figures of merit in the case of OES with low‐power and high‐power MIP, CMP, microwave plasma torch (MPT), MWP‐electrode sources including rotating field sustained plasma and H‐type MWP as well as microplasmas are given. There are also described cases of atomic absorption, fluorescence, and laser ionization with these sources. The developments in MS in the case of both low‐power and high‐power MWPs and in the case of various types of sample introduction techniques are discussed. Applications of MWP analytical spectroscopy are in the fields of biological samples with special reference to microanalysis, and of environmental and industrial samples with special emphasis on element speciation, on‐line monitoring, particle sizing, and direct solids analysis. A critical comparison of the methodology with other spectroscopic methods for the determination of the elements and their species is given.

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A thin-layer chromatography-mass spectrometry (TLC-MS) setup for characterization of low molecular weight compounds separated on standard TLC plates has been constructed. This new approach successfully combines TLC separation, laser ablation, and ionization using flowing atmospheric pressure afterglow (FAPA) source. For the laser ablation, a low-priced 445-nm continuous-wave diode laser pointer, with a power of 1 W, was used. The combination of the simple, low-budget laser pointer and the FAPA ion source has made this experimental arrangement broadly available, also for small laboratories. The approach was successfully applied for the characterization of low molecular weight compounds separated on TLC plates, such as a mixture of pyrazole derivatives, alkaloids (nicotine and sparteine), and an extract from a drug tablet consisting of paracetamol, propyphenazone, and caffeine. The laser pointer used was capable of ablating organic compounds without the need of application of any additional substances (matrices, staining, etc.) on the TLC spots. The detection limit of the proposed method was estimated to be 35 ng/cm2 of a pyrazole derivative.Graphical abstractSchematic illustration of new TLC-FAPA setup with diode laser ablation

The flowing atmospheric pressure afterglow (FAPA) ion source operates in the ambient atmosphere and has been proven to be a promising tool for direct and rapid determination of numerous compounds. Here we linked a FAPA-MS system to an electrochemical flow cell for the identification of drug metabolites generated electrochemically in order to study simulated metabolic pathways. Psychostimulants and their metabolites produced by electrochemistry (EC) were detected on-line by FAPA-MS. The FAPA source has never been used before for an on-line connection with liquid flow, neither for identification of products generated in an electrochemical flow cell. The system was optimized to achieve the highest ionization efficiency by adjusting several parameters, including distances and angles between the ion source and the outlet of the EC system, the high voltage for plasma generation, flow-rates, and EC parameters. Simulated metabolites from tested compounds [methamphetamine (MAF), para-methoxy-N-methylamphetamine (PMMA), dextromethorphan (DXM), and benzydamine (BAM)] were formed in the EC cell at various pH levels. In all cases the main products were oxidized substrates and compounds after N-demethylation. Generation of such products and their thorough on-line identification confirm that the cytochrome P450 - driven metabolism of pharmaceuticals can be efficiently simulated in an electrochemical cell; this approach may serve as a step towards predictive pharmacology using a fast and robust design.

This paper reviews the most common methods of generation of plasmas using microwaves with special emphasis on recently developed microwave plasma (MWP) sources for analytical applications. The art and science of microwave plasma optical and mass spectroscopy instrumentation (MWP-OES/MS), and the applications are briefly presented, including very recent advances in the field as of 2012. The design and operation of MWPs is discussed to provide a basic understanding of the most important selection criteria when designing MWP systems. The various plasma generation systems described include single-electrode capacitive microwave plasmas, electrodeless inductively coupled plasmas, multi-electrode systems energized with stationary or rotating fields. We also discuss various technical realizations of MWP sources for selected applications. Examples of technical realizations of plasmas in closed structures (cavities), in open structures (surfatrons, planar plasma sources), and in magnetic fields (Hammer cavity) are discussed in detail. Finally, we mention micro-and mini-discharges as convenient sources for miniaturized spectrometric systems. Specific topics include fundamental aspects of MWP, i.e., recent advances in the construction of analytical MWPs (coaxially coupled cavities, strip-line technology, multi-point energizing, power combining, rotating fieldexcited plasmas), operational characteristics, analytical characteristics and applications. Special reference is made to coupling with OES for determination of chromatographic effluents and particle sizing. The developments in elemental and molecular MS applications in both low-power and high-power MWPs are also discussed.

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