Purification device: activated carbon, molecular plug

Warm flow device: ensure the carrier gas flow rate is 30~100ml/min, and the variation fluctuation is <1%

packed column

Capillary column: The hollow column with coated wall, porous layer and coated carrier requires less sample and has fast analysis speed. However, the column capacity is low and requires high detector sensitivity.

Principle: Based on the different thermal conductivity of various substances and carrier gases, the resistance values ​​of the measuring arm and the reference arm are not equal, and the bridge is unbalanced, so there is a signal output. The greater the difference between the thermal conductivity of the mixed gas and that of the pure carrier gas, the larger the output signal will be.

Features: stable, versatile, low sensitivity

The sensitivity is 10^3 times that of TCD, with small dead volume, fast response, wide linear range, stable and commonly used, but not universal, and only responds to carbon-containing organic compounds.

Mechanism: chemical ionization rather than thermal ionization. In the flame, carbon-containing organic matter first splits into free radicals, then reacts with oxygen to produce positive ions, and then reacts with water to produce H3O ions. The positive ions (CHO, H3O) and electrons produced by chemical ionization move directionally toward the polarizing pole and collecting pole respectively under the action of the electric field to form a current, which is then amplified and recorded.

The electron capture detector is a highly selective detector with high sensitivity to electronegative substances (including halogen, sulfur, phosphorus, nitrogen, etc.)

The disadvantage is that the linear range is narrow, easily affected by experimental conditions, and reproducibility is poor. The disadvantage is that the linear range is narrow, easily affected by experimental conditions, and reproducibility is poor.

The greater the concentration of the sample component, the stronger the electronegativity, the greater the probability of capturing electrons, and the larger the inverted peak.

A chemiluminescence detector that responds to the characteristic wavelengths of organic compounds containing sulfur and phosphorus

Principle: When sulfur and phosphorus compounds are burned in a hydrogen-rich flame, chemiluminescent substances are generated and emit light of characteristic wavelengths.

Stationary phase: solid adsorbent such as silica gel, alumina, etc., the most commonly used is 5~10 μm silica gel adsorbent

Mobile phase: various single or multi-component solvents of different polarities. Generally, n-hexane and cyclohexane are used as the basic solvents, and dichloromethane, short-chain alcohols, and THF are added to adjust the elution strength.

Applicable objects: polar compounds, compounds or families containing different functional groups, isomer compounds

Peak order: alkyl group < halogen (F < Cl < Br < I) < ether < nitro compound < nitrile < tertiary amine < ester < aldehyde < primary amine < amide < carboxylic acid < sulfonic acid

Stationary phase: early application of fixative will result in loss of fixative and is rarely used.

Stationary Phase

Advantages: long life, chemical bonding, no loss of stationary solution, resistance to mobile phase impact; fast mass transfer, no deep depressions on the surface, faster mass transfer than ordinary liquid stationary phases; good selectivity, can bond different functional groups to improve selectivity; available Convenient for gradient elution

The influence of mobile phase separation in reversed-phase bonding chromatography: the lower the polarity of the solvent, the stronger the elution ability; the higher the polarity, the weaker the elution ability. Water is the weakest solvent for reversed-phase chromatography.

Improve separation: mobile phase ratio, mobile phase type, gradient elution

Principle: Add "ion pair" reagents into the reversed-phase chromatography mobile phase to form "counter ions" with the ionizable components in the sample, and separate ionic compounds on the reversed-phase chromatography column.

Anion separation: Alkylammoniums, such as tetrabutylammonium hydroxide or cetyltrimethylammonium hydroxide, are often used as counter ions.

Cation separation: Alkylsulfonic acids, such as sodium hexanesulfonate, are often used as counter ions.

principle

Stationary phase: anion and cation exchangers, grafted organic quaternary amine or sulfonic acid groups on organic polymers or silica gel

Mobile phase: salt buffer solution (with certain pH and ionic strength)

Among the basic components of ion chromatography, the most important and different from other high-performance liquid chromatography are the suppressor and conductivity detector.

Principle: Separation is based on the volume of molecules in the solution, and large molecules are eluted first

Features: low separation efficiency, easy to predict chromatographic behavior

Stationary phase: soft gel, semi-hard gel, hard gel, inorganic gel, organic gel

Principle: Based on biological specificity rather than relying on physical-chemical properties

Features: High selectivity, biocompatibility