HIGH-FIELD C-13 SOLID-STATE NMR-STUDIES OF STREAM HUMIC AND FULVIC-ACIDS WITH FAST MAGIC-ANGLE-SPINNING

Standard samples of stream humic and fulvic acids have been studied by high-resolution C-13 solid-state NMR. The spectra have been recorded at a high (9.4 T) magnetic field using (HC)-H-1-C-13 cross-polarizatio n (CP) and proton high-power decoupling (HPDEC) with fast (up to 15 kH z) magic-angle spinning (MAS). The widths of the spectral lines decrea se with increasing spinning rate. This is probably due to the overlap of spinning sidebands with resonances at low speeds and to a more effe ctive averaging of anisotropic broadening at high speeds. However, fas t MAS modulates the CP signal intensities, making quantitative analysi s very difficult.