CARBON-13 NUCLEAR MAGNETIC RESONANCE FOR A HUMIC AND A FULVIC ACID

Abstract

We carried out a 13C NMR solution study on a humic and a fulvic acid from a mineral soil. T1 values were 0.2 to 2.O s, with maximum values for carboxyl and methoxyl carbons, and nOes were up to 1 (theoretical maximu 2). Qualitative spectra were effectively obtained with short acquisition times (0.1 to 0.2 s), small pulse angles, and interpulse delays of less than 1 s. Spectra with essentially quantitative intensity distributions using inverse-gated decoupling were obtained with 45° pulses and delays (decoupler off) of 1 to 2 s. J-modulated spin-echo NMR (“multiplicity sorting‘’) provided explicit information on numbers of protons directly bonded to different types of carbons, consistent with previous chemical shift assignments. Spin-echo spectra with delays of 0.1 to 100 ms did not reveal any significant hidden sharp components in the humic acid spectrum, but resolution was enhanced; the smallest line widths in normal and spin-echo spectra were approximately 12 Hz.