Detailed explanation of the working principle of Thermo Scientific

The Thermo Scientific Gas Chromatograph uses a column to separate the mixture and then uses a detector to sequentially detect the separated components. The column is a few millimeters in diameter filled with a solid adsorbent or liquid solvent, and the filled adsorbent or solvent is called the stationary phase. There is also a mobile phase corresponding to the stationary phase. The mobile phase is a gas that does not react with both the sample and the stationary phase, typically nitrogen or hydrogen.

The sample to be analyzed is injected into the mobile phase at the top of the column, and the mobile phase carries the sample into the column, so the mobile phase is also called the carrier gas.

The carrier gas is continuously flowing through the column at a constant flow rate during the analysis; the sample is injected only once, and the analysis result is obtained once per injection. The separation of the sample in the column is based on differences in thermodynamic properties. The stationary phase has different affinities with the components in the sample (the adsorption force is different for the gas-solid Thermo Fisher gas chromatograph, and the solubility is different for the gas-liquid distribution Thermo Scientific gas chromatograph). When the carrier gas carries the sample continuously through the column, the component with high affinity moves slowly in the column, because the high affinity means that the stationary phase pulls it with great force. If the affinity is small, the movement is fast. The four column tubes are actually one, which is only used to indicate the state of each component in the sample at different instants.

The sample is a mixture of three components A, B, and C. When the carrier gas has just brought them into the column, the three are completely mixed, as in state (I). After a certain period of time, that is, the carrier gas took them over a distance in the column, the three began to separate, as in state (II). Moving on, the three are separated, as in states (III) and (IV). The fixed relative affinity is A>B>C, so the moving speed is C>B>A. Component C, which is in front of zui, first enters the detector immediately after the column, as in state (IV), and then B and A also enter the detector in sequence.

The detector gives a corresponding signal for each incoming component. The carrier gas is injected from the sample into the timing starting point, and after the components are separated, the detector is sequentially entered into the detector, and the time that the detector gives the large signal (commonly called peak value) corresponding to each component is called the component. Retention time tr. Practice has shown that the retention time tr of the different components is also constant when the conditions (including the carrier gas flow rate, the material and properties of the stationary phase, the length and temperature of the column, etc.) are constant. Therefore, in turn, it can be inferred from the retention time which substance the component is. Therefore, the retention time can be used as the basis for qualitative analysis of Thermo Scientific Gas Chromatography Instruments.