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Gas chromatography (GC) is an older analytical technique that is still widely used today. It is a technique that can be used with both inorganic and organic analytes, but the one requirement is that the sample must be volatile, otherwise the analysis won’t work. The technique has seen a lot of use across many industries and it is often coupled with other techniques, most commonly mass spectrometry. Here, we’re going to look at how gas chromatography works.
气相色谱法
Gas chromatography is often used to determine the purity of an unknown substance or to separate out the components of an unknown mixture so that each of the different parts can be analyzed. It is a technique that can be used to detect samples in very small quantities. Overall, these instruments have an inlet area, where the carrier gas and sample are injected into the instrument, a chromatographic column which is heated to ensure that all the components are gases, and a detector area which can vary depending on the needs of the analysis.
像任何色谱仪器一样，内部工作原理包括流动阶段和固定阶段。它确实与许多其他色谱技术（例如液相色谱（LC），高性能液相色谱（HPLC）和薄层色谱法（TLC）（TLC）等其他不同的色谱技术不同，它具有液体移动相，因为气体色谱中的流动相是一种惰性气相。所使用的载气通常是氦，氩气或氮。
固定相可以由几种材料组成，但通常是聚合物或其他惰性材料，即欧洲杯足球竞彩一个不会与分析的任何气态分子反应的一种，因为任何反应会导致固定相降解。虽然固定相是一种高度堆积的固体，但通常涂有一个具有高沸点的液体固定相。
气相色谱的工作原理
The general working principles are as follows. The sample is injected into the instrument where it is vaporized and mixes with the carrier gas to become a part of the mobile phase. This mobile phase is then carried through the chromatographic column where it interacts with the stationary phase of the column. The interactions between the stationary phase and the analyte determine the elution time of the different molecules in the sample, because if the sample interacts with the stationary phase more, then it will take longer to reach the detector.
此外，固定相具有分子孔，不同大小的分子可以通过。因此，如果分子较小，则其洗脱时间比较大的分子更快。因此，样品中分子的洗脱时间与特定检测器的分析相结合，可用于确定样品中的分子及其比率。通常连接到气相色谱的检测器包括质谱仪（GC-MS），火焰电离检测器（FID），导热率检测器（TCD）和电子捕获检测器（ECD）。
Parameters that Affect the Instrument
There are a number of factors and changeable parameters that can affect how the instrument will perform. These can be split into the properties of the sample and the changeable parameters of the instrument itself.
One factor that can influence the results of the analysis is the vapor pressure of the sample, which in turn is related to the polarity of the molecules in the sample. The polarity of a molecule affects the boiling point of the molecule, which in turn changes the vapor pressure of the molecule. In general, if a molecule has a lower boiling point, it will have a higher vapor pressure and this means that it will elute quicker because it will spend more time in the gas phase than interacting with the stationary phase.
除了改变沸点外，分子的极性还会影响其直接与色谱柱固定相相互作用的程度。因此，如果固定相本质上是极性的，则极性分子与在非极线中相比需要更长的时间。
Other Systematic Parameters
还有许多系统的参数可以影响气相色谱分析的结果。这些包括对色谱柱温度，载气流量，柱长度以及注入分析的材料量的变化。可以对不同的参数进行调整以使分析更快（对于所有被分析的分子），但这有时可以以质量较低的分离为代价。峰在光谱上不那么区分。
就色谱柱温度而言，分子会更快地洗脱，但是分子之间几乎没有任何分离，因为它们中的大多数将保持在气相中，而不是与固定相相互作用。当载气流量增加时，也是相同的情况。另一方面，更长的列将改善分离，因为沿着列有更多的区域可以交互。虽然较长的列将按比例增加洗脱时间，但如果使用长度太长的列长度，则会导致光谱上的洗脱峰因纵向扩散增加而扩大。
至于所使用的样品材料的浓度，重要的是不要使用过多。气相色谱光谱峰通常是对称的，并且引入过量的分析物会导致这些峰尾巴。不需要很多分析物，因为它是一种高度敏感的技术。
结论
Overall, the consensus is that a high flow rate and temperature can decrease the elution time of all the molecules in the sample, leading to a faster analysis, but it comes at the cost of a quality separation, so compromises need to be made to balance both aspects.
资源
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