Atmospheric chromatograph

Atmospheric chromatographworking principle

The chromatograph uses a chromatographic column to separate the mixture first, and then uses a detector to sequentially detect the separated components. The diameter of a chromatographic column is several millimeters, and it is filled with solid adsorbent or liquid solvent, which is called the stationary phase. There is also a mobile phase corresponding to the fixed phase. The mobile phase is a gas that does not react with either the sample or the stationary phase, typically nitrogen or hydrogen. The sample to be analyzed is injected into the mobile phase at the top of the chromatographic column, which carries the sample into the column. Therefore, the mobile phase is also known as the carrier gas. The carrier gas flows continuously through the chromatographic column at a certain flow rate during the analysis process; And the sample is only injected once, with each injection yielding an analysis result. The separation of samples in chromatographic columns is based on differences in thermodynamic properties. The components in the stationary phase and sample have different affinities (different adsorption forces for gas-solid chromatography and different solubility for gas-liquid distribution chromatography). When the carrier gas continuously passes through the chromatographic column with the sample, the component with high affinity moves slowly in the column because high affinity means that the stationary phase has a strong pulling force on it. Those with lower affinity move faster. The four column tubes are actually one, used only to represent the states of each component in the sample at different moments. The sample is a mixture composed of components A, B, and C3. When the carrier gas first introduces them into the chromatographic column, the three are mixed together, as in state (I). After a certain period of time, when the carrier gas carries them through the column for a certain distance, the three begin to separate, as in state (II). Continuing forward, the three will separate, such as states (III) and (IV). The fixed relative affinity between them is A>B>C, so the moving speed is C>B>A. The component C that walks ahead first enters the detector immediately after the chromatographic column, such as state (IV), and then B and A also enter the detector in sequence. The detector provides a corresponding signal for each incoming component. The time elapsed from the injection of the sample into the carrier gas as the starting point for timing, to the separation of each component and subsequent entry into the detector, where the detector provides the maximum signal (commonly referred to as the peak) corresponding to each component, is called the retention time tr of each component. Practice has shown that under certain conditions (including carrier gas flow rate, material and properties of the stationary phase, length and temperature of the chromatographic column, etc.), the retention time tr of different components is also constant. Therefore, conversely, the substance of the component can be inferred from its retention time. Therefore, the retention time can be used as the basis for qualitative analysis of chromatographic instruments.

The signal provided by the detector for each component appears as peaks on the recorder, which is called chromatographyPeak. The maximum value on the chromatographic peak is the basis for qualitative analysis, while the area included in the chromatographic peak depends on the content of the corresponding component, so the peak area is the basis for quantitative analysis. The curve recorded by a recorder after injecting a mixture sample is called a chromatogram. Qualitative and quantitative analysis results can be obtained by analyzing the chromatogram.

The structure of a gas chromatograph. The carrier gas is provided by the carrier gas cylinder, and after passing through the carrier gas flow control valve to stabilize the flow and the rotor flowmeter to detect the flow, it is sent to the sample gasification chamber. The sample vaporization chamber is equipped with rings to vaporize the liquid sample. If the sample to be analyzed is a gas, the gasification chamber does not need to be heated. The gasification chamber itself is the injection chamber, through which samples can be injected into the carrier gas. The carrier gas enters the chromatographic column with the injected sample from the injection port, and after separation, it sequentially enters the detector before being emptied. The signal provided by the detector is amplified and recorded by the recorder as the chromatogram of the sample.

Gas chromatograph is a separation and analysis tool for multi-component mixtures, which uses gas as the mobile phase and employs column chromatography technology with flushing method. When multi-component analytical substances enter the chromatographic column, due to the different distribution coefficients between the gas phase and the fixed liquid liquid phase of each component in the chromatographic column, the operating speed of each component in the chromatographic column is also different. After a certain column length, they leave the chromatographic column in sequence and enter the detector. After detection, they are converted into electrical signals and sent to the data processing workstation, thus completing the qualitative and quantitative analysis of the analyte.

Atmospheric chromatographScope of application

Environmental Protection: Analysis, Monitoring, and Research of Trace Toxic Substances in Polluted Areas such as Atmospheric Water Sources

Biochemistry: clinical applications, pathology, and toxicology research;

Food Fermentation: Analysis and Study of Trace Components in Microbial Beverages;

Chinese and Western medicine: analysis of raw materials, intermediates, and finished products;

Petroleum processing: analysis and control of petrochemicals, petroleum geology, oil composition, and mineral control research;

Organic chemistry: component research and production control in the field of organic synthesis;

Health Inspection: Analysis and Research on Labor Protection Pollution Detection;

*Science: Military detection, control, and research;