Characterization of 15N-TNT Residues After an Anaerobic/Aerobic Treatment of Soil/Molasses Mixtures by Solid-State 15N NMR Spectroscopy. 1. Determination and Optimization of Relevant NMR Spectroscopic Parameters

Solid-state 15 N NMR was applied to a humic acid, extracted from 15 N-2,4,6-trinitrotoluene (TNT) enriched soil treated in an anaerobic/aerobic composting system to characterize the nitrogen functionality of the transformation products bound to the soil organic material. Signals assignable to aniline derivatives and condensation products were identified, indicating that the anaerobic/aerobic treatment caused a reduction of nitro groups followed by condensation reactions with the soil organic material. Relevant parameters for routine application of the cross polarization magic angle spinning technique were determined and optimized. The proton spin-lattice relaxation times of all peaks in the 15 N NMR spectrum of the humic acid did not exceed 30 ms. Due to the fast relaxation, the application of 15 N NMR spectroscopy to soils with lower enrichment of 15 N-TNT is feasible. The influence of spinning sidebands on the intensity distribution was shown to be minimal at spinning speeds between 5.5 and 6.5 kHz. Contact times between 0.7 and 1 ms resulted in spectra with representative intensity distribution of all visible 15 N-TNT transformation products. However an underestimation of unreacted TNT must be considered. The results imply that CPMAS 15 N NMR is a valuable tool for the examination of bound residues of TNT in soils. (Figure 1).