色谱仪的重要性

王天泽

Gas chromatography is one of the most widely used techniques for analyzing hydrocarbon mixtures。Some of the advantages of chromatography are the range of measurement (from ppm levels up to 100 %), the detection of a wide range of components, and the repeatability of the measurements.Chromatography is used in the laboratory, in permanently installed online systems, and in the field with portable systems.No matter the location, style, or brand, all gas chromatographs are composed of the same functional components: the sample handling system, the chromatograph oven,and the controller electronics (refer to Figure 1).
分析碳氢化合物的混合物气相色谱法是应用最广泛的技术之一。一些色谱法的优点是测量范围（从ppm水平到100%）,各种组件的检测和测量的可重复性。无论用在实验室、在线分析或者是便携式分析。无论是品牌、安装形式，所有的气体色谱分析都是由功能组件：样品处理、预热箱、控制器组成的。（如图一）


Sample Handling System 样品处理系统
The gas chromatograph uses very small diameter gas paths and significant restrictions to flow; therefore, the sample injected to the analyzer must be dry and free of solids. Additionally, the gas chromatograph requires samples to be injected at a pressure significantly different than the source of the sample. The sample handling system should control the sample pressure and remove solid and liquids to ensure the sample presented to the gas chromatograph is clean and dry. The stream selection on multistream applications is also a function of the sample handling systems and is usually performed by simple solenoid valves.气相色谱仪使用直径非常小的气路和流动显著限制;因此，注入到分析仪样品必须干燥，不含固体。此外，气相色谱仪，需要样品比采样的源显著不同的压力下被注入。样品处理系统应控制样品压力和去除固体和液体，以确保呈现给气相色谱仪样品是清洁和干燥。关于多数据流的应用程序的流选择也是样品处理系统的一个功能，通常通过简单的电磁阀执行。
Most gas chromatographs require the sample to be controlled typically to between 15 and 30 PSIG (100 and 200 kPaG). In the majority of applications, the sample will be at considerably higher pressures, so the sample pressure must be regulated down to within the acceptable range. An important consideration is the Joules-Thompson effect in which the temperature of a gas will decrease as the pressure is reduced. Whereas the amount of cooling is dependent on the composition of the gas, a typical value used.for estimating the cooling of natural gas is seven degrees Fahrenheit per 100 PSI (American Gas Association, n.d.) or 5.6 ℃ per 1000 kPa. As the temperature of a hydrocarbon gas mixture is reduced, eventually some of the larger hydrocarbon components will begin to drop out of the gas phase into the liquid phase. The temperature at which this begins to occur is the hydrocarbon dew point. If the sample is near the hydrocarbon dew point when it is sampled, the temperature of the gas may drop below this point when the pressure is regulated down, and the composition of the gas will change as the heavy components drop out as liquids.
许多气相色谱仪要求进行的样品通常控制在15到30PSIG之间（100-200kPaG）。在大多数的应用中，样品处于相当高的压力，因此样品的压力必须在可接受的范围内被调节下降。一个重要的考虑因素是焦耳-汤普森效应，其中随着压力降低的气体的温度将降低，而冷却的量取决于该气体的组成。


Chromatograph Oven 色谱仪烤箱
Chromatograph Columns 色谱柱
Analysis Valves 分析阀门
Detectors 探测器
Gas Chromatograph Controller 气相色谱仪控制器

王天泽

The goal of the sample handling system is to preserve the composition of the gas, so it is important to consider the detrimental effects that the Joules-Thompson effect may have on the sample.The use of heated regulators, insertion regulating probes (which use the heat from the flowing gas in the pipeline to maintain the temperature of the regulated sample), and heated sample handling components such as heat-traced tubing is highly recommended to ensure that the temperature of the sample is maintained to at least 30 ℉ (16.7 ℃) above the hydrocarbon dew point (American Petroleum Institute, 2006).
Inline filters are typically used to remove solid particles down to twomicrons in size. The larger the volume inside the sample handling system, the longer the lag time between when the sample enters the probe and when it enters the gas chromatograph. To avoid introducing large sample lag times into the system, particulate filters should not have large volumes, so coalescing filters are generally not recommended. Many sample probes in use today include a particulate filter at the filter tip. These are highly recommended as they stop contamination entering the system; however, users must routinely remove the probe and replace the filters to ensure the sample flow through the filter/probe is sufficient.Liquids can be removed using membrane filters that use a specially designed membrane that only permits gas to pass through. The membrane can be located on the probe tip or in a membrane filter/separator located on the gas chromatograph sample handling system. The typical liquid membrane filter passes the sample gas through the membrane and sweeps the removed liquids away through a bypass flow path (refer to Figure 2). The bypass flow also allows the sample lag time to be reduced as it provides for a faster flow rate from the probe to the analyzer sample handling system (up to 500 cc/min) than the flow rate into the gas chromatograph, which is typically 30 cc/min to 50 cc/min.

谁来翻译一下这三段

王天泽

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