Quantitative C-13 NMR analysis of lignins with internal standards

Novel protocols for acquiring quantitative C-13 NMR spectra of lignins have been developed using the internal reference compounds 1,3,5-trioxane and p entafluorobenzene. Trioxane offers a convenient internal standard for colle cting inverse gated proton decoupled C-13 NMR spectra for lignins, whereas pentafluorobenzene can be used to provide information on the amount of meth ine carbon using the DEPT experiment. In each case, the internal reference compounds provide single, un-overlapped sharp signals in the middle of the spectral region, permitting facile integration. These integrals could be us ed to determine the amounts of different structural features of lignins, ex pressed in absolute units of millimoles per gram. The optimum parameters fo r these experiments were validated for a variety of spectrometer platforms, and standard errors were determined for different spectral areas using lig nin model compounds and "standard" lignins. In addition, the data derived f or the International Round Robin "standard" lignins showed good agreement w ith the data from quantitative P-31 NMR spectroscopy and published data, ob tained by independent laboratories using independent methods of analysis.