Elemental detection with a microwave-induced plasma/gas chromatograph-mass spectrometer system

Abstract

Development of a technique that uses a low-pressure microwave-induced plasma (MIP) for selective elemental detection In a combined gas chromatograph/mass spectrometer (GC-MS) system is described. With this technique, complex organic molecules are converted Into a few simple neutral species by passage through the MIP unit. The elements present In the original molecules determine which species will be formed in the MIP. In a hydrogen-rich plasma, oxygen forms CO and H20, sulfur forms CS2, nitrogen forms HCN, chlorine forms HCI, and carbon forms, CH4, C2H2, C2H4, and C2He. Identification and quantification of these simple neutral species enable elemental composition information for the original molecules to be determined. Detection of elemental C, N, O, S, and Cl and measurement of elemental C/O and C/N ratios In a variety of compound types and structures by the MIP/GC-MS technique are discussed. With the relatively unsophisticated mode of operation used, the dynamic range for the technique Is 400, and the sensitivity limit for elemental carbon passing through the MIP Is 0.3 yug/s.

The potential of a modified rf glow discharge source for enhanced elemental speciation studies

“…15 However, no parent molecular ions were observed with this cell. This is consistent with the observation of Heppner, 16 suggesting that the compounds were fully ionized in the plasma, and the fragments are recombinants of the ions rather than fragments from the original molecules. The increasing ion signal ratios may then be caused by collisional dissociation of the molecular fragment ions with increased pressure.…”

Selective detection of carbon-13, nitrogen-15, and deuterium labeled metabolites by capillary gas chromatography-chemical reaction interface/mass spectrometry

“…The combination of capillary gas chromatograph (GC) and a chemical reaction interface/mass spectrometer (GC-CRIMS) allows the analyst to selectively detect stable isotope labeled substances as they elute (6). Heppner (7) described a microwave-induced plasma/gas chromatograph-mass spectrometer (MIP/GC-MS) method which was mechanically different but similar in principle to CRIMS. A high-energy plasma coverted compounds eluting from a gas chromatograph to stable molecules in the presence of hydrogen.…”

Plasma-source mass spectrometry for speciation analysis: state-of-the-art

“…Coupled with the ability to directly determine halogens and a moderate tolerance of molecular species, MIPs are a natural choice as an element-selective detector for gas chromatography. Indeed, the first GC-MIP studies performed in 1965 [137] were followed by the introduction of a commercial GC-MIP-AES system [138], which has enjoyed extensive use for the analysis of a wide range of environmental samples. Analysis of pesticides by this method is particularly attractive because the microwave plasma is capable of generating simultaneous quantitative information for carbon-, chorine-, sulfur-and phosphorous-containing molecules or can provide molecular ions to help identify the parent pesticide species [139].…”