Degradation, early detection spectrometry

In early mass spectrometry applications of lasers, the sample was irradiated directly by a laser beam to desorb intact sample-related ions [27]. In this direct mode, termed laser desorption/ionization (LDI), the extent of energy transfer is, however, difficult to control and often leads to excessive thermal degradation. Also, not all compounds absorb radiation at the laser wavelength and thus are not amenable to LDI. Only those compounds that have mass below 1000 Da can be analyzed by LDI. Analytical sensitivity is also poor. A key contribution of LDI experiments is the observation that the desorption efficiency of amino acids and peptides that absorb the laser fight beam is greater than those without the chromophore [28]. IR lasers (e.g., an Nd YAG laser at 1.06 p m and a pulsed CO2 laser at 10.6 pm) and UV lasers (frequency-quadrapled Nd YAG laser at 266 nm) have aU been used. The detection of malaria parasites in blood by LDI with an N2 laser has been demonstrated [29]. 

Our early work with dinoseb, a nitrophenolic herbicide commonly found as a soil contaminant, showed that under microaerophilic conditions, it is transformed to persistent multimeric forms that remain toxic, while under well-aerated conditions, no degradation occurs (29). However, in studies pre-dating our munitions work, we enriched an anaerobic consortium that fermented dinoseb and other nitroaromatic compounds under methanogenic conditions (16, 17). These initial observations ultimately led to our treatment of soils containing complex mixtures of TNT, dinitrotoluenes, mononitrotoluenes, nitrobenzoates, and related compounds (33), which showed that all contaminants could be removed to below detection limits of gas chromatography/mass-spectrometry. Even though biological treatment of several of these compounds in well-aerated cultures has been described, many of them are subject to polymerization reactions under microaerophilic conditions, which are almost certain to occur in soil treatment systems that are not maintained absolutely anoxic (18). 

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