注意在气相色谱及其物理方法

气相色谱法(GC)是一种常用的色谱分析化学分离和分析化合物可以蒸发而不分解。气相色谱法(GC)通常用于测试一个特定物质的纯度或分离混合物的各种组件。气相色谱法(GC)可用于制备色谱分离纯化合物的混合物。气相色谱也可称为气相色谱法(VPC)或GasA¢€“液分配色谱法(GLPC)。这些替代的名字,以及他们的缩写是常用的科学文献。气相色谱是分离的化合物的混合物注入气体或液体样品移动阶段通常被称为载气和天然气通过固定相。在大多数情况下,流动相是一种惰性或惰性气体,如氦、氩、氮和氢。固定相是一个微观层粘性液体在固体粒子表面惰性固体支持在一个列上的玻璃或金属油管。在一些列,固体颗粒的表面也可以作为固定相。

窄管的气相色谱仪是由称为蒸发样本的列是由一个连续流动的惰性或不反应的气体。组件的示例通过列以不同的速率取决于他们的化学和物理性质和由此产生的交互作用列衬里或填充定义为固定相。通常情况下,列被放置在一个温控烤箱。

当这些化学物质到达的最后列电子检测和识别。S / SL(分裂/分裂更少)注射器样品引入激烈的小室通过一隔syringe-the热挥发的艾滋病样本和样本矩阵。载气然后扫描整个样本(分割模式)或部分样本(模式)分割成列。在分裂模式下,分裂通风排气装置部分样本/运载气体混合物在注射室。在处理样品分析浓度高(> 0.1%)分裂注入是首选,而分割不注入是最适合痕量分析分析浓度较低(0.01%)。分割阀打开在预定的时间分割模式少清洗更重的元素,否则污染系统。

气源入口或气体开关阀气体样本收集瓶是连接到一个最常用的六端口切换阀。样本可以扩展到之前撤离样品环载气流量不受打扰。样品环的内容插入到载体气流切换。惰性气体是通过水沸腾样本使不溶性挥发性化学物质被净化的矩阵。在室温下挥发物“困”在吸收剂列(也称为一个陷阱或集中器)。挥发物被定向到运载气体流陷阱后加热。载气(流动相)的选择是至关重要的。在效率方面氢气的流量与氦。如果流量优化氦可能更有效率,并提供最好的分离。氦是不易燃的,兼容更广泛的探测器和旧的仪器。 As a result, helium is the most commonly used carrier gas. However, the cost of helium has risen significantly in recent years prompting an increasing number of chromatographers to switch to hydrogen gas. The continued preferential use of helium may be due to historical use rather than rational consideration. The Flame Ionization Detector (FID) and the Thermal Conductivity Detector (TCD) are two commonly used detectors. While TCDs are advantageous in that they are non-destructive their low detection limit for most analytes prevents their widespread use. FIDs are primarily sensitive to hydrocarbons and are more sensitive than TCD. Because FIDs do not detect water or carbon dioxide they are ideal for environmental organic analyte analysis. The Flame Ionization Detector (FID) detects analytes two to three times more sensitively than Thermal Conductivity Detector ((TCD). The Thermal Conductivity Detector (TCD) is based on the thermal conductivity of matter passing around a tungsten-rhenium thin wire with a current flowing through it. Helium or nitrogen serve as the carrier gas in this configuration due to their relatively high thermal conductivity which keeps the filament cool while maintaining uniform resistivity and electrical efficiency. As analyte molecules elute from the column and mix with carrier gas thermal conductivity decreases while filament temperature and resistivity increase resulting in voltage fluctuations and eventually a detector response. Detector sensitivity is proportional to filament current and inversely proportional to the detector's immediate environmental temperature as well as the carrier gas flow rate. Electrodes are placed adjacent to a hydrogen/air-fueled flame near the exit of the column in a Flame Ionization Detector (FID) and when carbon-containing compounds exit the column they are pyrolyzed by the flame. Due to the ability of carbons to form cations and electrons upon pyrolysis which generates a current between the electrodes this detector only works for organic/hydrocarbon containing compounds. The increase in current is translated into a chromatogram peak. FIDs have low detection limits (a few picograms per second) but they cannot produce ions from carbonyl-containing carbons. Helium, hydrogen, nitrogen and argon are all FID compatible carrier gases.