Characterization of N-15-TNT residues after an anaerobic/aerobic treatmentof soil/molasses mixtures by solid state N-15 NMR spectroscopy. 1. Determination and optimization of relevant NMR spectroscopic parameters

Solid-state N-15 NMR was applied to a humic acid, extracted from N-15-2,4,6 -trinitrotoluene (TNT) enriched soil treated in an anaerobic/aerobic compos ting system to characterize the nitrogen functionality of the transformatio n products bound to the soil organic material. Signals assignable to anilin e derivatives and condensation products were identified, indicating that th e anaerobic/aerobic treatment caused a reduction of nitro groups followed b y condensation reactions with the soil organic material. Relevant parameter s for routine application of the cross polarization magic angle spinning te chnique were determined and optimized. The proton spin-lattice relaxation t imes of all peaks in the N-15 NMR spectrum of the humic acid did not exceed 30 ms. Due to the fast relaxation, the application of N-15 NMR spectroscop y to soils with lower enrichment of N-15-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 m s resulted in spectra with representative intensity distribution of all vis ible N-15-TNT transformation products. However an underestimation of unreac ted TNT must be considered. The results imply that CPMAS N-15 NMR is a valu able tool for the examination of bound residues of TNT in soils. (Figure 1) .