Volatile fatty acids (VFAs) are among the most important parameters in process monitoring of anaerobic digestion plants for biogas production. The concentration of single VFA species is typically determined by direct injection of the acidified aqueous phase of digestate samples into GC-FID. Analysis of dimethyl carbonate extracts was investigated as an alternative method consisting of a simple and rapid in-vial procedure of acidification and solvent extraction of the sample, followed by centrifugation and GC-MS analysis. The principal figures of merit resulting from internal standard calibration were comparable to those proposed for the direct analysis of aqueous digestate, while the analysis of real samples did not provide statistically significant differences between the two methods according to parametric and non-parametric tests. Procedural aspects including sample amount and solid removal improved with dimethyl carbonate, while GC contamination was reduced. The method was applied to seventeen samples from fully operating anaerobic digesters fed with various feedstocks and enabled the individuation of high probability of system stress through the values of total VFA, propanoic acid, longer chained VFA concentrations and the ratio between acetic and propanoic acid concentrations. The use of dimethyl carbonate allowed the detection of alicyclic and aromatic acids that could represent new molecular markers in assessing the origin of feed and process conditions.

中文翻译：

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碳酸二甲酯溶剂萃取-气相色谱-质谱法测定消化物中的挥发性脂肪酸

挥发性脂肪酸 (VFA) 是用于沼气生产的厌氧消化装置过程监控中最重要的参数之一。单一 VFA 种类的浓度通常通过将消化物样品的酸化水相直接注入 GC-FID 来确定。碳酸二甲酯提取物的分析作为一种替代方法进行了研究，该方法由简单快速的样品酸化和溶剂提取的小瓶程序组成，然后离心和 GC-MS 分析。由内标校准产生的主要品质因数与建议用于直接分析含水消化物的那些品质因数相当，而根据参数和非参数测试，实际样品的分析没有提供两种方法之间的统计学显着差异。使用碳酸二甲酯改善了包括样品量和固体去除在内的程序方面，同时减少了 GC 污染。该方法应用于来自完全运行的厌氧消化器的 17 个样品，这些样品用各种原料进料，并通过总 VFA、丙酸、较长链 VFA 浓度以及乙酸和丙酸浓度之间的比率的值，实现了系统压力的高概率个体化。碳酸二甲酯的使用允许检测脂环族酸和芳族酸，它们可以代表评估进料来源和工艺条件的新分子标记。该方法应用于来自完全运行的厌氧消化器的 17 个样品，这些样品用各种原料进料，并通过总 VFA、丙酸、较长链 VFA 浓度以及乙酸和丙酸浓度之间的比率的值，实现了系统压力的高概率个体化。碳酸二甲酯的使用允许检测脂环族酸和芳族酸，它们可以代表评估进料来源和工艺条件的新分子标记。该方法应用于来自完全运行的厌氧消化器的 17 个样品，这些样品用各种原料进料，并通过总 VFA、丙酸、较长链 VFA 浓度以及乙酸和丙酸浓度之间的比率的值，实现了系统压力的高概率个体化。碳酸二甲酯的使用允许检测脂环族酸和芳族酸，它们可以代表评估进料来源和工艺条件的新分子标记。