Headspace gas chromatograph

气相色谱（GC）可定性和定量测定挥发性脂肪酸（VFA），即短链有机酸，其是生物废水处理过程（例如厌氧消化、除磷和反硝化）中的重要中间体。在我们的实验室中，需要VFA测量来监控这些过程。 由于基质废水或污泥复杂，样品在进行GC分析前通常需要经过酸化、离心、过滤、蒸馏、衍生化和萃取等一系列预处理过程，不仅耗时（每份样品约2小时），而且溶剂购买和废物处理费用也很高。我们每天分析数十个样品，这些样品来自我们正在进行的粪便和污泥厌氧消化、除磷和脱氮项目，我们负担不起冗长的样品制备过程。 我们目前使用简单过滤后直接进样。因此，GC进样器和色谱柱系统暴露于样品中溶解的污染物中，需要每天清洁和频繁更换附件，如色谱柱和插入衬垫等。这些广泛的仪器服务不仅降低了样品通量，而且价格昂贵。顶空气相色谱可以避免这些问题，并通过在线样品制备提供相对快速和无溶剂的分析。在顶空气相色谱法中，VFA首先转化为气相，然后引入气相色谱中，液体中的污染物被留下，干扰最小化。我们现有的气相色谱系统主要用于分析永久性气体，对于液体样品（如废水中的VFA）的容量有限。在其他大学实验室中使用顶空分析样品需要数周时间，并且不能依赖于大多数日常研究场景，特别是动态研究。总而言之，我们目前的GC正在努力解决来自脏废水或污泥样品的污染问题，只有新的顶空GC可以解决这个问题，从而有效地交付我们的资助工作。

Gas chromatograph (GC) allows qualitative and quantitative determination of volatile fatty acids (VFA) i.e. short-chain organic acids which are important intermediates in biological wastewater treatment processes such as anaerobic digestion, phosphorus removal and denitrification. VFA measurement is required to monitor these processes in our laboratory. Due to the complex matrix wastewater or sludge, the samples usually require a series of pretreatment processes such as acidification, centrifuge, filtration, distillation, derivatisation and extraction etc. prior to GC analysis, which is not only time consuming (about 2 hours per sample), but also costly in terms of solvent purchase and waste disposal. We analyze dozens of samples per day from our ongoing anaerobic digestion of manure and sludge, phosphorus removal and denitrification projects and can ill afford a lengthy sample preparation procedure. We are presently using direct sample injection following simple filtration. As a result, the GC injector and column systems are exposed to the dissolved contaminants in samples and require daily cleanup and frequent replacement of accessories such as column and insert liner etc. These extensive instrumental services not only reduce the sample throughput, but again are expensive. Headspace GC can avoid these problems and offer relatively rapid and solvent-free analyses through online sample preparation. In the headspace GC, VFA is first converted into gas phase and then introduced into GC, the contaminants in liquid are left behind with minimization of interferences. Our existing GC system is designed primarily for analysis of the permanent gases and it has limited capacity for liquid samples such as VFA in wastewater. Analyzing samples using headspace in the other university labs requires weeks and cannot be relied on for most of daily research scenarios, especially for dynamic studies. In summary, our present GC is struggling with contamination from the dirty wastewater or sludge samples and only a new headspace GC can solve the problem leading to effective delivery of our grant work.