Microwave-induced plasma emission spectrometers

Common gas chromatographic detectors that are not element- or metal-specific, atomic absorption and atomic emission detectors that are element-specific, and mass spectrometric detectors have all been used with the hydride systems. Flame atomic absorption and emission spectrometers do not have sufficiently low detection limits to be useful for trace element work. Atomic fluorescence [37] and molecular flame emission [38-40] were used by a few investigators only. The most frequently employed detectors are based on microwave-induced plasma emission, helium glow discharges, and quartz tube atomizers with atomic absorption spectrometers. A review of such systems as applied to the determination of arsenic, associated with an extensive bibliography, is available in the literature [36]. In addition, a continuous hydride generation system was coupled to a direct-current plasma emission spectrometer for the determination of arsenite, arsenate, and total arsenic in water and tuna fish samples [41]. 

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... 

A rapid method of analysis of organo-tin compounds in sediment and biological CRMs was developed (Pereiro et al., 1997). Ethylated butyltin compounds were separated isothermally on a multicapillary (MC) gas chromatographic column in less than 30 s as compared with 5-10 min on a regular capillary column. The MC column consisted of a bundle of about 900 1 m-long, 40 mm i.d. coated capillaries. The column was connected to a microwave-induced plasma atomic emission spectrometer. Phenyltin compounds were also included in the procedure. Detection limits of MBT, DBT and TBT were about 0.2ngml 1 (as tin). 

As noted earlier, USNs have been employed for sample insertion into atomic spectrometers suoh as flame atomio absorption spectrometry (FAAS) [9,10], electrothermal atomic absorption speotrometry (ETAAS) [11], atomic fluorescence spectrometry (AFS) [12,13], induotively ooupled plasma-atomic emission spectrometry (ICP-AES) [14,15], inductively coupled plasma-mass spectrometry (ICP-MS) [16,17] and microwave induced plasma-atomic emission spectrometry (MIP-AES) [18,19]. Most of the applications of ultrasonic nebulization (USNn) involve plasma-based detectors, the high sensitivity, selectivity, precision, resolution and throughput have fostered their implementation in routine laboratories despite their high cost [4]. 

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. 

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. 

In the atomic emission detector (AED), the effluent from the GC column is introduced into a microwave-induced plasma (MIP), an inductively coupled plasma (ICP), or a direct current plasma (DCP). The MIP has been most widely used and is available commercially. The MIP is used in conjunction with a diode array or charge-coupled-device atomic emission spectrometer as shown in Figure 27-12. The pl ma is sufficiently en-... 

Several detectors are used for VOCs analysis by GC flame ionization detector (FID), photo ionization detector (PID), electron capture detector (BCD), electrolytic conductivity detector (ELCD), mass spectrometer detector (MSD or MS), and Fourier-transform infrared detector (FTIRD). For the in-depth reviews of the detectors, readers are directed to Refs. [52-54]. Examples of ICP-MS or microwave-induced plasma atomic emission spectrometry (atomic emission detector, AED) have been reported as detection technique after chromatographic separation [55,56]. Current trends and developments in GC analysis of VOCs have been recently reviewed by the group of Dewulf [16,57]. Mass spectrometer detectors allow low detection limits in single/selected ion monitoring (SIM) and a qualitative confirmation by full scan mode or by means of other ion selected as qualifier. 

Analytical evaluation of a reduced-pressure microwave-induced plasma system with an optical emission spectrometer. 

The AED employs a microwave-induced He plasma to dissociate eluted analyte molecules to their component atoms and excite them to emit at characteristic wavelengths. This is very similar to the mechanism in the argon plasma inductively coupled plasma source (cf. Section 7.3.1). A spectrometer with a diode array detector (Figure 7.26b and c) isolates and measures the intensity of sensitive emission lines unique to each element. Depending on the relative sensitivity and proportion of atoms in the molecules, separate element response channels may display peaks in several element-selective chromatograms. These data may be combined with retention... 

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