What are the principles and compositions of liquid chromatography and gas chromatography?

The basic principle of chromatographic separation: there are two phases in chromatography, and one phase is fixed, which we call stationary phase; The other phase continues to flow through the stationary phase, which we call the mobile phase. The separation principle of chromatography is to use the different affinities of various substances to be separated in two phases. The mobile phase (gas, liquid) containing the sample passes through the surface of the stationary phase fixed in the column or plate and is immiscible with the flow. When the mixture carried in the mobile phase flows through the stationary phase, the components in the mixture will interact with the stationary phase. Due to the different properties and structures of each component in the mixture, the magnitude and intensity of the force generated between each component and the stationary phase are also different. With the movement of the mobile phase, the mixture is repeatedly distributed and balanced between the two phases, so that the components are retained by the stationary phase for different times, thus flowing out of the stationary phase in a certain order. Combined with appropriate post-column detection methods, the components in the mixture can be separated and detected.

HPLC can be divided into high-pressure infusion pump, chromatographic column, sampler, detector, fraction collector and data acquisition and processing system.

High pressure infusion pump

Function drives mobile phase and sample to pass through chromatographic separation column and detection system; Performance requirements: stable flow (1), high pressure resistance (30 ~ 60 MPa), and resistance to various mobile phases, such as organic solvents, water and buffers; Types of reciprocating pumps and diaphragm pumps.

chromatographic column

Functional separation of various substances in the sample; 10 ~ 30cm long, 5mm inner diameter and polished inner wall stainless steel pipe string; The particle size of the filler is 5 10μm, which is an efficient particle stationary phase.

sample injector

The function of introducing the sample to be analyzed into the chromatographic system; ① type syringe, with the size below 10Mpa, 10μm micro syringe, ② stop the sample flow, ③ introduce the sample by valve, which is common and ideal, with variable volume, and can fix ④ automatic sampler, which is beneficial to repeated operation and automation.

explorer

The function of converting the concentration change of the analyzed group in the column effluent into light or electric signal; Classification ① Differential refraction chemical detector ② Ultraviolet absorption detector ③ Ultraviolet compatible spectrophotometric detector ④ Diode array ultraviolet detector ⑤ Fluorescence detector ⑤ Electrochemical detector.

fraction collector

Function If chromatographic separation is not for pure chromatographic analysis, but for other spectral identification, or in order to obtain a small amount of test samples for a small amount of preparation, fraction collection is necessary; Methods ① Manual operation, less scores, complicated procedures and easy to make mistakes; ② The fraction collector has ideal collection and accurate microcomputer control operation.

Data acquisition and processing system

The function displays the signal detected by the detector.

Gas chromatograph:

GC mainly uses the differences of boiling point, polarity and adsorption properties of substances to realize the separation of mixtures, and its process is shown in the flow chart of gas phase analysis. The sample to be analyzed is brought into the chromatographic column by inert gas (carrier gas, also called mobile phase) after vaporizing in the vaporizing chamber, and the column is filled with liquid or solid mobile phase. Because the boiling point, polarity or adsorption properties of each component in the sample are different, each component often forms a distribution or adsorption equilibrium between the mobile phase and the stationary phase. However, because the carrier gas is flowing, this balance is actually difficult to establish. It is precisely because of the flow of carrier gas that the sample components are repeatedly distributed or adsorbed/desorbed during the movement. As a result, the components with high concentration in the carrier gas first flowed out of the chromatographic column and then flowed out of the stationary phase. When the components flow out of the chromatographic column, they immediately enter the detector. The detector can convert the sample components into electrical signals, and the magnitude of the electrical signals is directly proportional to the amount or concentration of the detected components. When these signals are amplified and recorded, it is a gas chromatogram.

( 1)

The gas path in the gas chromatograph of carrier gas system is a closed pipeline system in which the carrier gas runs continuously. The whole carrier gas system requires pure carrier gas, good air tightness, stable flow and accurate flow measurement. (2) The sampling system is to quickly and quantitatively add gas or liquid samples to the upper end of the chromatographic column. (3) The core of the separation system is the chromatographic column. Its function is to separate multi-component samples into single components. Chromatogram is divided into packed column and capillary column. (4) The function of the detector of the detection system is to convert the sample components separated from the chromatographic column into electrical signals according to their characteristics and contents. After amplification, the chromatogram was recorded by a recorder. (5) Signal recording or microcomputer data processing system In recent years, gas chromatograph mainly adopts chromatographic data processor. Chromatographic data processor can print recorded chromatograms and processing results, such as retention time, mass fraction of tested components, etc. , on the same recording paper. (6) Temperature control system is used to control and measure the temperature of chromatographic column, detector and gasification chamber, and it is an important part of gas chromatograph.