Mass spectrometric detector continued

In a well-equipped laboratory it is mandatory that these three techniques be coupled with a mass spectrometric detector in order to achieve a combination of resolution of mixtures, positive identification of separated organics and the high sensitivity that is essential when dealing with environmental samples. The penetration of mass spectrometers in recent years is indicated by the fact that of the 50 types of organic compound that have been determined by gas chromatography in 21 cases mass spectrometric detection is discussed. This trend will, no doubt, continue. 

GC continues to play an important role in the identification and quantification of ubiquitous pollutants in the environment. GC coupled with an electron capture detector (ECD) or a mass spectrometric detector (MSD) has been widely applied for the quantification of PCBs. 

The development of gas chromatography/mass spectrometry (GC/MS) and liquid chromatogra-phy/mass spectrometry (LC/MS) was possible only with the invention of interfaces that bridged the gap between the working parameters of each independent method. For GC/MS, the GC column operates above atmospheric pressure, and for packed columns, dilutes the sample in a considerable flow of carrier gas. For LC, a continuous stream of solvent exits the column, carrying sample along in dilute solution. The interface of each method to a mass spectrometric detector must be designed... 

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]. 

Atomic (AAS, DCP-AES) detectors have been coupled to robotic stations either through a continuous system acting as interface [ 11,29] or by direct aspiration into an ICP-AES instrument from a sample vial following treatment by the robot [30]. Mass spectrometric and NMR detectors used in this context are also based on direct aspiration. 

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