Microwave-induced plasmas

A Practical Approach to Quantitative Metal Analysis of Organic Matrices 

A Tesla coil is used to create a spark to generate the argon or helium plasma. The electrons generated oscillate in the microwave field and gain sufficient kinetic energy to ionise either gas by rapid and violent collisions. This is achieved by using a microwave frequency of 2500 MHz. Elements such as fluoride, chloride, bromide, iodide, sulphur, phosphorous, and nitrogen, which are not possible to measure by ICP-AES or DCP-AES, can be measured by MIP. 

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Gases for mixing with argon, such as N2 and Xe, have been the subject of study for some time. Some new instrumentation tvill incorporate manifolds for making this process easier. Other plasma developments include microwave-induced plasmas with He to eliminate interferences from argon containing molecular species. 

The intrinsic drawback of LIBS is a short duration (less than a few hundreds microseconds) and strongly non-stationary conditions of a laser plume. Much higher sensitivity has been realized by transport of the ablated material into secondary atomic reservoirs such as a microwave-induced plasma (MIP) or an inductively coupled plasma (ICP). Owing to the much longer residence time of ablated atoms and ions in a stationary MIP (typically several ms compared with at most a hundred microseconds in a laser plume) and because of additional excitation of the radiating upper levels in the low pressure plasma, the line intensities of atoms and ions are greatly enhanced. Because of these factors the DLs of LA-MIP have been improved by one to two orders of magnitude compared with LIBS. 

Minganti V, Capelli R, Depellegrini R (1995) Evaluation of different derivatization methods for the multielement detection of Hg, Pb and Sn compounds by gas chromatography-microwave induced plasma-atomic emission spectrometry in environmental samples. Fresenius Journal of Analytical Chemistry, 351 (4-5) 471 77. 

Huang M, Hirabayashi A, Shirasaki T, Koiznmi H (2000) A multimicrospray nebulizer for microwave-induced plasma mass spectrometry. Anal Chem 72 2463-2467 Ivanovich M, Murray A (1992) Spectroscopic methods. In Uranium-Series Disequilibrium Applications to Earth, Marine, and Enviromnental Sciences, 2" Ed. Ivanovich M, Harmon RS (eds) Orfbrd Univ. Press, Oxford... 

HPLC-QFAAS is also problematical. Most development of atomic plasma emission in HPLC detection has been with the ICP and to some extent the DCP, in contrast with the dominance of the microwave-induced plasmas as element-selective GC detectors. An integrated GC-MIP system has been introduced commercially. Significant polymer/additive analysis applications are not abundant for GC and SFC hyphenations. Wider adoption of plasma spectral chromatographic detection for trace analysis and elemental speciation will depend on the introduction of standardised commercial instrumentation to permit interlaboratory comparison of data and the development of standard methods of analysis which can be widely used. 

The most important advantages of MIP-AES as an analytical technique for GC detection of metals and metalloids are indicated in Table 7.32. MIP-AES is one of the most powerful analytical tools for selective detection in GC, and is potentially quantitative [331]. Elemental figures of merit for GC-MIP detection have been reported [332]. Microwave-induced plasmas have found much greater use in GC than in HPLC interfacing. Reviews on empirical and molecular formula determination by GC-MIP have been published [332,333]. 

As SFC provides gaseous sample introduction to the plasma and thus near-100 % analyte transport efficiency, coupling SFC with plasma mass spectrometry offers the potential of a highly sensitive, element-selective chromatographic detector for many elements. Helium high-efficiency microwave-induced plasma has been proposed as an element-selective detector for both pSFC and cSFC [467,468] easy hyphenation of pSFC to AED has been reported [213]. 

While most preliminary SFC-plasma coupled techniques employed microwave-induced plasmas (MIPs), the use of ICP-MS is now increasing [469]. An advantage of microcolumn SFC-ICP hyphenation is the significantly reduced flow-rates of microcolumns compared with those of conventional columns. Both pSFC-ICP-AES [470,471] and cSFC-ICP-AES [472] were described. In the case of elemental detector selectivity (e.g. AES) complete chromatographic resolution is not required. The detector possesses linearity over several orders of concentrative magnitude. Minimum detectable quantities for nonmetals range from sub to low ng mL"1. 

Principles and Characteristics The major drawbacks of ICP with argon as the support gas lie in numerous isobaric polyatomic ion interferences and in the lack of sufficient energy to ionise halogens and nonmetals to the necessary extent. With these weaknesses of ICP in mind, the possibility of generating microwave-induced plasmas with alternative gases to argon is of interest. 

E.H. Evans, J.J. Giglio, T.M. Castillano and J.A. Caruso, Inductively Coupled and Microwave Induced Plasma Sources for Mass Spectrometry, The Royal Society of Chemistry, Cambridge (1995). 

FSD Fourier self-deconvolution microwave-induced plasma... 

Methylated organo-selenium has been determined by GC/MS or fluorine-induced chemiluminescence to determine DMSe, DMDSe, and DMSeS. This last compound, dimethyl selenenyl sulfide, was mistakenly identified as dimethyl selenone (CH3Se02CH3) in earlier work with bacteria.181,182 However, much recent work with many microorganisms have shown ample evidence of DMSeS production from Gram-negative bacteria,181,183 phototrophic bacteria,167,184 phytoplankton185 and in B. juncea detailed above. SPME with microwave-induce plasma atomic emission spectrometry was recently used to... 

LOD in the range of 0.02 to 0.1 pg of lead, depending on the volatility of the species, were found after derivatizing with propyl or butyl Grignard reagents, GC separation and measurement by microwave-induced plasma AES124. 

Lansens, P., M. Leermakers, and W. Baeyens. 1991. Determination of methylmercury in hsh by headspace-gas chromatography with microwave-induced-plasma detection. Water Air Soil Pollut. 56 103-115. 

Lobinski et al. [72] optimized conditions for the comprehensive speciation of organotin compounds in soils and sediments. They used capillary gas chromatography coupled to helium microwave induced plasma emission spectrometry to determine mono-, di-, tri- and some tetraalkylated tin compounds. Ionic organotin compounds were extracted with pentane from the sample as the organotin-diethyldithiocarbamate complexes then converted to their pentabromo derivatives prior to gas chromatography. The absolute detection limit was 0.5pg as tin equivalent to 10-30pg kg-1. 

River and marine sediments, soils Bu3Sn BujSn BuSn Capillary glc-helium microwave induced plasma emission spectrometric detection 0.0001-0.0003 [72] ... 

Microwave-induced plasma atomic emission Plasma... 

J.M. Gehihausen, J.W. Carnahan, Determination of aqueous fluoride with a helium microwave-induced plasma and flow injection analysis. Anal. Chem. 61 (1989) 674-677. 

Story WC, Caruso JA. 1993. Gas chromatographic determination of phosphorus, sulfur and halogens using a water-cooled torch with reduced-pressure helium microwave-induced plasma mass spectrometry. J Anal Atomic Spectrometry 8 571-575. 

Further designs of ion sources applied in plasma spectroscopy such as electrodeless microwave induced plasmas (MIPs) operating in a noble gas atmosphere at low power (mostly below 200 W) or capacitively coupled microwave plasma using Ar, He or N2 the as plasma gas (at 400-800 W) were described in detail by Broekaert.33 Microwave plasmas produced by a magnetron are operated at 1-5 GHz. Their special application fields for selected elements and/or element species are based (due to the low power applied) in atomic emission spectrometry.33... 

Activities for miniaturizing mass spectrometers (e.g., microplasma on chip or insertion of diode lasers in RIMS), for constructing cheaper and more compact instrumentation with the same performance or improved properties compared to existing instruments are required as the next generation mass spectrometers. The introduction of microwave induced plasmas or of p,-torches to reduce Ar gas consumption involves developments in this future direction. 

Microwave-induced plasma optical emission spectrometry (MIP-OES) is very sensitive for volatile species containing metals. Hence its use has been also proposed as a detector in the development of hyphenated techniques for speciation. GC MIP-OES has been successfully applied for the speciation of alkylmetal species of low molecular weight (Hg, Sn and Pb compounds) in many different environmental applications [23]. 

I. Rodriguez Pereiro and A. Carro Diaz, Speciation of mercury, tin and lead compounds by gas chromatography with microwave-induced plasma and atomic-emission detection (GC-MIP-AED), Anal. Bioanal. Chem., 312, 2002, 74-90. 

J. M. Costa-Fernandez, F. Lunzer, R. Pereiro, N. Bordel and A. Sanz-Medel, Direct coupling of high-performance liquid chromatography to microwave-induced plasma atomic emission spectrometry via volatile-species generation and its application to mercury and arsenic speciation, J. Anal. At. Spectrom., 10, 1995, 1019-1025. 

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