Short-chain fatty acids (SCFAs) are gut microbiota metabolites recognized for their beneficial effects on the host organism. In this study, a simple and rapid sample preparation method combined to SCFAs analysis by direct injection and gas chromatography coupled with flame ionization detection (GC-FID), for the determination and quantification of eight SCFAs (acetic, propionic, i-butyric, butyric, i-valeric, valeric, i-caproic and caproic acids) in rat, mice and human faeces and in fermentation fluids samples, has been developed and validated. The method consists of extraction of the SCFAs by ethyl ether after acidification of the samples. The effect of the number of extractions has been assessed in order to optimize the procedure and to obtain a satisfactory yield for all the analyzed SCFAs. The increase of the extracted analytes quantity was significant passing from 1 to 2 and from 2 to 3 extractions (P < 0.05), while no significant differences were found performing 3, 4 or 5 extractions (P > 0.05). The SCFAs extracted are directly analyzed by GC-FID without derivatization and separated on a polyethylene glycol nitroterephthalic acid modified coated capillary column, with a chromatographic run time of 13 min. The proposed method showed good sensitivity, with limits of quantifications in the range 0.14-0.48 µM for SCFAs from propionic to caproic acids and 2.12 µM for acetic acid; recovery was between 80.8 and 108.8% and intraday and interday repeatability in the range 0.6-5.0% of precision (RSD, %) The optimized method is suitable for the quantitative analysis of SCFAs in real samples of rat, mouse and human faeces and in fermentation fluids, and it can be applied also to very small amount of faecal sample (20 mg).

中文翻译：

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GC-FID方法的开发和验证，该方法可用于分析大鼠和人类粪便以及发酵液中的短链脂肪酸。

短链脂肪酸（SCFA）是肠道微生物群代谢产物，因其对宿主生物的有益作用而被认可。在这项研究中，一种简单，快速的样品制备方法与直接进样和气相色谱结合火焰电离检测（GC-FID）结合用于SCFA的分析，用于测定和定量八种SCFA（乙酸，丙酸，异丁酸，丁酸）已开发并验证了大鼠，小鼠和人类粪便以及发酵液样品中的异戊酸，异戊酸，戊酸，异己酸和己酸）。该方法包括在样品酸化后用乙醚萃取SCFA。已经评估了萃取次数的影响，以优化程序并为所有分析的SCFA获得令人满意的收率。从1到2和从2到3次萃取，萃取的分析物数量显着增加（P <0.05），而进行3、4或5次萃取则没有显着差异（P> 0.05）。提取的SCFAs可直接通过GC-FID分析，而无需衍生化，并在聚乙二醇硝基对苯二甲酸改性的带涂层毛细管柱上分离，色谱运行时间为13分钟。所提出的方法显示出良好的灵敏度，对于从丙酸到己酸的SCFA，定量限为0.14-0.48 µM，对于乙酸为2.12 µM。回收率在80.8至108.8％之间，日内和日间重复性在精度（RSD，％）的0.6-5.0％范围内。优化的方法适用于大鼠真实样品中SCFA的定量分析，