Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries , D-12587 Berlin, Germany.
Department of Chemistry, Humboldt-Universität zu Berlin , D-12489 Berlin, Germany.
Anal Chem. 2017 Dec 19;89(24):13449-13457. doi: 10.1021/acs.analchem.7b03729. Epub 2017 Nov 29.
A novel approach for the analysis of dissolved lignin in freshwaters is presented. Lignin concentrations in natural water samples are low, and a lignin extraction is usually required to obtain sufficient material for analysis. In this study, the alkaline CuO oxidation, which liberates a set of lignin-derived phenols, is performed directly on 15 mL of water sample in a microwave digestion system, hence reducing the required sample amount and preparation time considerably. These features make the method particularly suitable to study diagenetic changes of dissolved lignin in small-scale laboratory or field experiments. Phenol separation and quantification by gas chromatography tandem mass spectrometry lead to method detection limits between 22.7 and 1260 ng/L for single phenols, which corresponds to minimum lignin concentrations in the range of 8.5 μg/L (Σ), offering applications for wetland, river, and lake waters with high terrestrial dissolved organic matter inputs. As a general method improvement, we present the addition of EDTA during phenol workup. EDTA binds remaining copper, thereby speeding up sample flow through the solid phase sorbent during phenol extraction and, furthermore, prevents substantial phenol losses, which occur if a water sample contains nitrate. Three natural water samples, a fresh leaf leachate and two humic-rich lake waters, were analyzed by the direct method presented here and in comparison with the established C18 extraction approach. Results show a similar reproducibility of both methods but reveal lower absolute lignin phenol yields in the humic-rich lake water samples upon C18 extraction.
提出了一种分析淡水溶解木质素的新方法。天然水样中的木质素浓度较低，通常需要进行木质素提取才能获得足够的分析材料。在这项研究中，直接在微波消解系统中对 15 毫升水样进行碱性 CuO 氧化，从而释放出一组木质素衍生的酚类物质，这大大减少了所需的样品量和制备时间。这些特点使该方法特别适合于在小规模实验室或野外实验中研究溶解木质素的成岩变化。通过气相色谱串联质谱法对苯酚进行分离和定量，得到单酚的方法检出限为 22.7 至 1260ng/L，对应的最小木质素浓度范围为 8.5μg/L（Σ），可应用于湿地、河流和湖泊等具有高陆地溶解有机物质输入的水域。作为一种通用的方法改进，我们在酚类工作流程中添加了 EDTA。EDTA 结合剩余的铜，从而在酚类提取过程中加快了样品通过固相吸附剂的速度，此外，如果水样中含有硝酸盐，还可以防止大量酚类物质的损失。用这里提出的直接方法和已建立的 C18 提取方法对三种天然水样（新鲜叶片浸提液和两种富腐殖质的湖水）进行了分析。结果表明，两种方法的重现性相似，但在 C18 提取时，富腐殖质的湖水中的绝对木质素酚类产量较低。
