气相色谱y: Principles, Types and Working - 万博max手机登录注册

What Is Gas Chromatography?

气相色谱y or Gas Liquid Chromatography is a technique applied for separation, identification and quantification of components of a mixture of organic compounds by selective partitioning between the stationary phase and mobile phase inside a column followed by sequential elution of separated components. The technique is suitable for separation of compounds having following characteristics :

High volatility
Thermal stability
低分子量

Purpose of gas chromatography

The main purpose of the gas chromatography technique is to separate the compounds that possess:

High volatility
低分子量
Thermal stability

How does gas chromatography work?

For having a hold on how does chromatography works, we need to be aware of the individual components of a GC chromatogram or GC Chromatograph.

The main components are:

Mobile phase

In gas chromatography, usually, three types of gases are employed namely –

Carrier gas –This is needed for the transfer of the injected sample to the separation column. They are also responsible for the subsequent transfer of separated components to the detector.常见的例子：氮，氦或氢
Fuel gas –他们支持火焰Flame ionization detector(FID) detector such as Hydrogen.
Zero air –These are the purified air that plays the role of oxidant to support the combustion of flame in the detector.Before being led to the gas chromatographic system, the above three are intermixed in the desired proportion.

Sample injector

喷油器是一个加热块，在其中注入样品。通过载气流，样品自发蒸发并导致色谱柱。

With the help of a gas-tight syringe, the liquid sample mixtures are injected whereas, with the help of automated injection valves, the gaseous mixtures are injected.

Column

这充满了固定相，或者其墙壁被液体吸附剂覆盖。这样做是为了选择性吸收和样品成分的保留。

Commonly used: Packed columns and Capillary columns (More popular)

Component of a Column – Oven

The column is enclosed by a column oven which is responsible for maintaining a constant temperature during isothermal operation. This temperature when temperature programming is needed can be increased in a controlled way for acquiring effective separation of mixture components possessing different volatilities.

Detector

This is employed for the identification and quantification of components.
Here, the regions of individual peaks created relate to their concentrations and their retention times are representative of their identity.

Common examples: Flame ionization detector, Thermal conductivity detector (TCD), and Electron capture detector (ECD).

数据系统

它是一组专用软件，可提供对许多重要的操作参数的控制，例如注射序列，清洗周期，过度温度控制，气体流速，检测器波长等。同时，数据站计算并显示参数。

图：GC的系统图

Gas chromatographic analysis

The X-axis – Retention time of peak (Rt)

This is calculated from the time the sample was injected into the column (t0)till it reaches the detector. Every analyte peak has a retention time that is measured from the apex of the peak, just liketR.

Y轴 - 检测器响应

This shows the measured response of the analyte peak within the detector.

The baseline here represents the signal received from the detector where no analyte is eluting from the column or is beneath the detection limit. It is considered as an indication of a problem or indication to check the maintenance, in situations where the baseline is found higher than usual.

Measurements such as width at the baseline, width at half height, area, and total height can be withdrawn from the peak.

For better sensitivity and better resolution, narrower, sharper peaks are desired.

测量的准确性受峰值存在的数据点总数的影响。

图：GC的色谱图输出。图片提供：Anthias Consulting.

类型

Majorly, there are twogas chromatography typesinto which it is classified – GLC or gas-liquid chromatography and GSC or gas-solid chromatography.

Both the methods use either liquid or solid as a stationary phase while using gas as the mobile phase. In Gas-solid chromatography, the retention of analytes is due to physical adsorption. On the other hand, gas-liquid chromatography separates the ions or molecules that are dissolved in a solvent.

基本原理是 - 随着样品解决方案与第二固体或液相接触，溶质将开始与其他相互作用。由于吸附速率不同，离子交换，分区或大小，相互作用将有所不同，这就是使混合组件彼此分离的原因。这些差异将使样品混合物以不同的速率通过色谱柱通过，并且可以分离化合物。

A Gas Chromatograph like any other analytical instrument has evolved from one with several knobs and dials to one having a simple microprocessor-based keypad to control the operational parameters.

The simplification has resulted in ease of operation and time-saving. An understanding of the main component parts will help in maximum utilization of system capabilities.

Dimensions of Gas Chromatography

气相色谱y has a high peak capacity in comparison to other separation techniques. Although it has the ability to separate a huge number of compounds, there are a few applications that require thousands of peaks to be separated and we don’t have enough theoretical plates to separate them through chromatography.

一个常见的例子是柴油的分析that involves identifying trace analytes in complex matrices, such as food samples or environmental samples.

没有完整的铬可进行分析atographic resolution through spectral resolution, where MS is hyphenated with GC. However, this technique can be successful under the condition that the coeluting peaks have different spectra.

Heart-cutting works well where the majority of the peaks are separated through a column and then a few groups of coeluting peaks are cut and transferred to a new column consisting of different stationary phase and selectivity. If the samples are complex with frequent co-elutions, two-dimensional chromatography is used.

Gas chromatography applications

Since the discovery of the gas chromatographic system, the areas of Gas chromatography applications is ever-increasing which includes:

Pharmaceutical industry
Research
Medical and Forensic
Environmental monitoring (both inside laboratories, and natural water bodies)
Petroleum refining and petrochemicals
Edible oils
口味、饮料和食品ustry
Fragrance industry (Cosmetics)
聚合物和塑料
农药

气相色谱y: Limitations and Common Issues

Limitations

manbetx官方气相色谱法是广泛使用在许多industries for routine analysis, research or analysing hundreds and thousands of compounds in different samples and components from solids to gases. This technique is quite robust and can be easily mixed or coupled with other distinctive techniques, such as mass spectrometry.

但是，只有当它们的manbetx官方分子量约为1250 U时，气相色谱才能分析氦/氢的挥发性化合物。在热不稳的化合物的情况下，GC中高温暴露会降解它们。

Cold injection techniques and low temperatures can be used to minimize that. To prevent polar analytes from getting lost or stuck in GC, the system must be well-maintained and the analytes must be derivatized.

Issues

One of the major problems with gas chromatography is leakage. As the mobile phase is a gas that flows through the system, leakage may occur. Therefore, it is crucial to ensure that the parts and consumables are correctly installed and the system is regularly checked for leakage.

Another problem is the activity for more polar analytes, especially the ones at trace levels. Issues like irreversible adsorption or reactant breakdown can also occur due to dirt build-up in the system and silanol groups on the glass liners and columns.

Most problems are seen on the inlet area where the sample is injected, transferred and vaporized into the GC column. Hence, ensuring proper maintenance of the inlet and use of correct consumable is essential.

Glossary of GC terms

The glossary will help you familiarize with the terminology in case you are not already familiar withthegas chromatography working technique.

Stationary Phase	A solid phase which absorbs the sample components and later releases them in a sequential manner
移动阶段	A stream of carrier gas used for transporting sample from injection port to the column to the detector
Column Oven	A compartment inside which the column is mounted. It maintains a constant temperature or a varying temperature in response to a set temperature programme.
Detector	A device which gives the signal response in terms of area counts under a peak
Column Efficiency	用HETP表示，表示GC列的解决能力
Packed Column	A steel or glass tube wound as a coil which holds the stationary phase
毛细管柱	A fused silica capillary column that holds the liquid absorbent on the tube on its walls
Autosampler	A device capable of holding several samples, standard vials and automatically injects a predetermined sample volume into the gas chromatograph
Injector	精确样品卷的手册或自动化设备简介
FID	Flame Ionisation detector which responds to most organic compounds
TCD	Thermal Conductivity detector. Universal and nondestructive detector
ECD	电子捕获探测器。对于含有电负元素的化合物，例如卤素
NPD	Nitrogen Phosphorus detector. Specific for compounds containing nitrogen or phosphorus
FPD	Flame photometric detector.Specific for sulphur and phosphorus containing compounds
MSD	Mass Selective detector
GC – MS	Hyphenated technique using a combination of GC and Maas spectrometer
Fronting	Distortion of peak where the peak front appears distorted
Peak Tailing	峰的变形，峰的尾端出现扭曲
心切	A method which employs two columns of different selectivity. A selected portion of effluent from first column is passed to the second column
Temperature Programming	Changing temperature of column oven in a predetermined manner using a program
Retention Time	Time between injection and the maximum of the peak response
Syringe	Hand held device capable of injecting selected volume into the chromatograph
HETP	Height Equivalent to a theoretical plate. It is a measure of column efficiency and is expressed as an numerical value without units H = L/N The larger the number of theoretical plates the lower is HETP and better is the column efficiency
Septa	注射器内用于将样品引入色谱系统的橡胶或硅盘。样品注射时注射器穿透该盘
Ferrule	A plug made from graphite or grass for holding the column gas tight into the oven
Gas Regulator	设备由控制器组成以记录和控制气线中的压力，并监视气缸内部的压力
Gas Filter	一个壁挂式装配，包括能够去除入口气体中的水分，碳氢化合物，氧气和其他杂质的包装弹药筒
阴谋	Porous Layer Open Tubular column where an absorbent is bonded to the inner surface of the column. Useful for analysis of permanent gases or high volatility liquids.
SCOT	支撑涂层的开放管状柱。在固体支撑上支撑液体固定相，该固体支撑覆盖在毛细血管共同的内表面。
Split Injection	注入模式，其中一部分蒸发样品被排出，只有一小部分进入柱状头。这用于高度浓缩样品
Splitless Injection	在关闭吹扫阀的地方注入样品，整个样品进入色谱柱。然后打开清洗阀以冲洗喷油器
WCOT	墙涂层的开放管状柱。固定相粘合到毛细管柱的内壁
On-Column Injection	注射器进入并将样品输送到圆柱头的顶部
Leak test	A process to establish that all connections are leak free
Pre-vent	样品入口的设计，可将注入的样品拆分并排出一部分。残留部分仅针对列。当样品高度浓缩时，这是合适的

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