GC-microwave induces plasma

Gerbersmann C., Lobinski R. and Adams F.C. (1995) Determination of volatile sulfur compounds in water samples, beer and coffee with purge and trap GC-microwave-induced plasma atomic emission spectrometry. Anal. Chim. Acta 316, 93-104. 

The first GC-microwave-induced plasma emission system was reported in 1965 [23]. During the past two decades GC-plasma emission systems have gained in popularity and have been used for the identification and quantification of mercury, lead, tin, selenium, and arsenic compounds [13]. The most frequently used plasma source is the microwave-induced plasma operated either at reduced pressure or at atmospheric pressure with helium or argon as the plasma gases at powers of 100 to 200 W The Beenakker cylindrical resonance cavity introduced in 1976 [24], and since then modified to achieve better detection limits, is most frequently used in the GC-microwave-induced plasma emission systems that are easily adaptable to capillary GC operation. These microwave-induced plasma detectors respond to non-metals (H, D, B, C, N, O, F, Si, F S, Cl, As, Se, Br, I) and metals, with absolute detection limits in... 

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]. 

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. 

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. 

GC coupled with microwave-induced plasma spectrometric detection (GC-MIP)... 

After GC-AAS the GC coupled with microwave-induced plasma (GC-MIP) spectrometer is probably the most widely investigated hybrid system for speciation. The MIP is a low-power excitation source for emission spectrometry. In this... 

Figure 4.1 GC-MIP interface taken from The optimisation of an atmospheric pressure helium microwave induced plasma coupled with capillary gas chromatography for the determination of alkyl-lead and alkyl-mercury compounds (Greenway and Barnett, 1989).

Figure 6.1 Bar-graph of MeHg in CRM 580. The results correspond to six replicate determinations as performed by different laboratories using various methods. MEANS indicates the mean of laboratory means with 95% confidence interval. Abbreviations-. CVAAS, cold vapour atomic absorption spectrometry CVAFS, cold vapour atomic fluorescence spectrometry ECD, electron capture detection GC, gas chromatography HPLC, high-performance liquid chromatography ICPMS, inductively coupled plasma mass spectrometry MIP, microwave induced plasma atomic emission spectrometry QFAAS, quartz furnace atomic absorption spectrometry SFE, supercritical fluid extraction.

The microwave-induced plasma (MIP) is the most popular plasma used for conventional GC-OES. However, the DC glow discharge plasma has recently received more attention because it can be operated at a low temperature, albeit at a low pressure 1-30 Torr so as to avoid excessive gas heating and arcing. 

Figure 19 Helium microwave induced plasma (M1P) torch used in MIP mass spectrometry (MIP-MS) sampling for capillary gas chromatography (GC) detection. (From Ref. 110.)...

For clcmcnt-speciPc detection in GC, a number of dedicated spectrometric detection techniques can be used, for example, quartz furnace AAS or atomic Bu-orescence spectrometry (AFS) for Hg, or microwave-induced plasma atomic emission spectrometry (MIP-AES) for Pb or Sn. However, ICP-MS is virtually the only technique capable of coping, in the on-line mode, with the trace element concentrations in liquid chromatography (LC) and capillary electrophoresis (CE) efBuents. The femtogram level absolute LoDs may still turn out to be insufficient if an element present at the nanogram per milliliter level splits into a number of species, or when the actual amount of sample analyzed is limited to some nanoliters as in the case of CE or nanoBow HPLC. The isotope spcciPcity of ICP-MS offers a still underexploited potential for tracer studies and for improved accuracy via isotope dilution analysis. 

In practice, speciation analysis of metalorganic compounds is conducted using three coupled systems GC with microwave-induced plasma optical emission... 

The gas chromatograph may be interfaced with atomic spectroscopic instruments for specific element detection. This powerful combination is useful for speci-ation of different forms of toxic elements in the environment. For example, a helium microwave induced plasma atomic emission detector (AED) has been used to detect volatile methyl and ethyl derivatives of mercury in fish, separated by GC. Also, gas chromatographs are interfaced to inductively coupled plasma-mass spectrometers (ICP-MS) in which atomic isotopic species from the plasma are introduced into a mass spectrometer (see Section 20.10 for a description of mass spectrometry), for very sensitive simultaneous detection of species of several elements. 

Plasma sources are capable of producing intense emission from the elements. Types of plasma used in chromatographic detection are microwave induced plasmas (MIP) and inductively coupled plasma (ICP). An argon plasma is sustained in a microwave cavity which focuses into a capillary discharge cell. The most widely used cavities are cyhndrical resonance cavities and surfatron that operates by surface microwave propagation along a plasma column. Atmospheric pressure cavities are very simple to interface with capillary GC columns. 

Such large amounts of data can only be sensibly and rapidly analysed and compared with reference spectra using microprocessors such as the fast 32 bit processors in PCs. The main systems in use today are discussed below, and in addition to the above mentioned techniques the microwave induced plasma (MIP) detector, a helium microwave plasma emission source coupled to a GC and an optical emission spectrometer are reviewed. 

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