Gas Chromatography Method

Gas chromatography is a chromatographic separation analysis method using a gas as a mobile phase. The vaporized sample is carried by the carrier gas (mobile phase) into the column. The interaction between the stationary phase in the column and the components in the sample is different. Each component has a different time from the column and the components are separated from each other. With appropriate identification and recording systems, chromatograms are generated that indicate the time and concentration of each component exiting the column. According to the peak time and sequence shown in the figure, the compounds can be qualitatively analyzed; according to the height and area of the peaks, the compounds can be quantitatively analyzed. High performance, high sensitivity, selectivity, fast analysis, wide application, easy operation and so on. Suitable for qualitative and quantitative analysis of volatile organic compounds. Non-volatile liquids and solids can be pyrolyzed and analyzed after gasification. Can be used together with red light and harvesting spectroscopy or mass spectrometry, chromatography as a means to separate complex samples to achieve high accuracy. It is an important analytical method for the detection of organic compounds in forensic analysis.

Gas chromatography (GC) is a type of chromatography. There are two phases in chromatography, one phase is the mobile phase and the other phase is the stationary phase. If you use a liquid as the mobile phase, it is called liquid chromatography. When you use a gas as the mobile phase, it is called gas chromatography.

Gas chromatography can be divided into two types because of the different stationary phases used. Gas-solid chromatography using a solid adsorbent as a stationary phase and gas-liquid chromatography using a monomer coated with a fixed liquid as a stationary phase.

According to the principle of chromatographic separation, gas chromatography can also be divided into adsorption chromatography and distribution chromatography. In gas-solid chromatography, the stationary phase is an adsorbent, gas-solid chromatography belongs to adsorption chromatography, and gas-liquid chromatography belongs to distribution chromatography.

According to the chromatographic operation, the gas chromatography is a column chromatography. According to the different column thickness, it can be divided into two types: general packed column and capillary column. The general packed column is a stationary phase in a glass or metal tube with an inner diameter of 2 to 6 mm. Capillary columns can be further divided into two types: hollow capillary columns and packed capillary columns. Hollow capillary columns are coated with a fixed solution directly on the inner walls of glass or metal capillaries with inner diameters of only 0.1 to 0.5 mm. Filled capillary columns have only recently been developed. They contain certain porous solid particles in thick walls. Glass tube, then heated to pull into a capillary, the general diameter of 0.25 ~ 0.5 mm.

Detector

There are many types of detectors that can be used in gas chromatography. The most commonly used are the flame ionization detector (FID) and the thermal conductivity detector (TCD). Both detectors have a sensitive response to a wide variety of analytes and can measure a wide range of concentrations. TCD is inherently versatile and can be used to detect anything other than carrier gases (as long as their thermal conductivity is different from the carrier gas at the detector's detection temperature), whereas FID is primarily responsible for hydrocarbons. Sensitive. FID detection of hydrocarbons is more sensitive than TCD but cannot be used to detect water. Both detectors are powerful. Since the detection of TCD is non-destructive, it can be used in tandem with the destructive FID (connected before the FID) to give two complementary analyses of the same analyte.

Principle

The gas chromatography system consists of a liquid stationary phase and an adsorbent or inert solid contained in the column.

Breaks the mobile phase of the gas passing through the column. After the sample to be separated and analyzed is added from one end of the column, the adsorption or dissolving capacity of each component in the fixed sample is different, that is, the partition coefficient of each component between the stationary phase and the mobile phase is different. When the two phases are repeatedly dispensed and moved forward with the moving phase, the velocity of each component moving along the column is different, and the component with a small distribution coefficient is retained by the stationary phase for a short time, and can be quickly passed from the end of the column. Outflow. The concentration c at which each component elutes from the end of the column is plotted against the time t after injection, and the resulting figure is called a chromatogram.

Application

Any substance that can be vaporized without decomposition under the conditions allowed by the gas chromatograph can be determined by gas chromatography. Partially thermally unstable substances, or substances that are difficult to gasify, can be analyzed by gas chromatography by chemical derivatization.

Widely used in petrochemical, medical and health, environmental monitoring, biochemistry, food testing and other fields

1. Application in hygiene inspection

Air, water pollutants such as volatile organic compounds, polycyclic aromatic hydrocarbons, benzene, toluene, benzo  etc; residual organochlorine, organophosphorus pesticides in crops; food additives such as benzoic acid; body fluids and tissues and other biological materials Analysis of amino acids, fatty acids, vitamins, etc.

2. Application in medical examination

Analysis of biological fluids such as body fluids and tissues: fatty acids, triglycerides, vitamins, sugars, etc.

3. Application in drug analysis

Antiepileptic drugs, volatile components in Chinese patent medicines, and determination of alkaloids.