GC coupled with other atomic spectrometric detectors

3 GC coupled with other atomic spectrometric detectors 

Chemical ionisation, electron impact ionisation and field ionisation have been used to obtain molecular fragmentation patterns in speciation studies involving GC-MS. However, the systems used often lacked sensitivity. This area has expanded recently as inexpensive, smaller and more sensitive instruments have become available (Zufiaurre et al., 1997). Tributyl tin and triphenyl tin compounds have recendy been determined in seawater using GC negative ion chemical ionisation MS (Mizuishi et al., 1998). Of particular interest are those mass spectrometers in which the sample is broken down into elemental form. 

In recent years plasma MS has become very popular, especially where the ion source for the mass spectrometer is an ICP. These systems, which are available commercially, offer detection limits two to three orders of magnitude better than those for atomic emission detection (i.e. subpicogram levels for some elements) 

Plasma MS is usually based on quadrupole mass analysers. The atmospheric ICP, optimised for ion formation, is placed on its side facing a sample cone (Fig. 4.3). The mass spectrometer operates at reduced pressure and therefore a two- or three-stage differentially pumped interface is needed to transfer the ions from the plasma to the mass analyser. The interface for GC-ICP-MS is generally the same as for ICP emission systems. In one of the earliest GC-MS speciation studies (Chong and Houk, 1987) a packed GC column was used to obtain mass spectra of organic compounds with detection limits in the range 0.001-500 ngs The effects of isotopic fractionation by natural physico-chemical processes were also studied. 

The use of HPLC in hybrid systems has expanded rapidly over the last few years because it is particularly compatible with environmental water samples. These are 

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