Separation of benzoic and unconjugated acidic components of leonardite humic material using sequential solid-phase extraction at different pHs as revealed by FTICR MS and correlation NMR spectroscopyстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 25 декабря 2018 г.
Аннотация:Here we report on sequential solid phase extraction of leonardite hymatomelanic acid (CHM) on nonionic sorbent at four steadily lowered pH values: 7, 5, 3, and 2 yielding fractions with different acidic properties. Using NMR spectroscopy and ultra-high resolution mass-spectrometry we revealed a gradual shift of dominating scaffolds in the fractions of CHM from reduced saturated to oxidized aromatic compounds. An increase in the average aromaticity of the CHM fractions was accompanied by a red shift in fluorescence spectra. These results were supported by heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) NMR experiments. We have demonstrated that the CHM fraction isolated at pH 5 was dominated by aliphatic carboxyl carriers, while the pH 3 fraction was dominated by aromatic carboxyl acids. The developed fractionation technique will enable deeper insight on structure-properties relationships and design of the humic-based materials with tailored reactive properties.