Basic knowledge of chromatography

What is the basic principle of phase chromatography separation?

1. Utilize the components in the mixture to have different dissolution and desorption abilities in the mobile phase and stationary phase, or different adsorption and desorption abilities or differences in the effects of other affinity properties.

2. When the two phases are in relative motion, the components of the sample are repeatedly subjected to various forces in the two phases, so that the components in the mixture are separated.

Briefly describe the basic composition of the gas chromatograph.

The basic components consist of 5 components.

1. Pneumatic system; 2. Sample introduction system; 3. Separation system; 4. Detection system; 5. Recording system.

Briefly describe the characteristics of gas chromatography?
1. High separation efficiency;
2. High selectivity;
3. High sensitivity;
4. Fast;
5. Widely used.

What is retention time?

The time from the start of injection to the maximum value of the elution curve of each component can be used as a sign of the peak position of the chromatogram. This time is called the retention time and is expressed by t.

What is a chromatogram?

When the chromatographic column effluent passes through the detector system after injection, the response signal time or the volume of carrier gas outflow is called a chromatogram.

What is a chromatographic peak? Peak area?
1. The differential curve of the response signal generated when the chromatographic column effluent passes through the detector system is called the chromatographic peak.
2. The area enclosed by the peak from the peak back to the baseline is called the peak area.

How to measure the carrier gas flow rate?

High-end chromatographs are equipped with automatic test devices. Without automatic test devices, soap film flowmeters can be used to connect the soap film flowmeter to the test outlet (you can also disconnect the chromatographic column from the detector. Column one end), test the flow rate per minute. After the measurement, the indication of the chromatographic heating pressure gauge will increase because the temperature increases. The resistance of the chromatographic column to the gas increases. Do not adjust the pressure. When the chromatographic temperature increases, the steady flow indicator will not change. The test carrier gas flow rate is tested at room temperature.

How to control the carrier gas flow rate?

The control of the flow rate of the carrier gas is mainly reduced by the pressure reducing valve on the high pressure steel cylinder on the gas path, and then the pressure is stabilized by the instrument's pressure stabilizing valve, and then through the flow stabilizing valve to achieve the control of the carrier gas flow rate. Higher than the pressure after regulation. Non-programmed temperature chromatography generally does not have a steady flow valve, only relying on a regulator valve to control the flow rate.

How to measure its linear velocity by gas chromatography analysis?
1. Generally, the linear velocity is actually the dead time of the chromatographic column;
2. Methane is used as non-retentive substance, and the retention time of methane is measured (TCD detector uses air peak),
3. Divide the length of the column by the retention time of methane to obtain the average linear velocity of the column. How to choose the best operating conditions of carrier gas flow rate in gas chromatography analysis?

In chromatographic analysis, choose the best carrier gas flow rate to obtain the minimum height of the tray. Therefore, the optimal flow rate value can be obtained from the velocity theory on the peak shape expansion formula. Usually the inner diameter of the column is 4mm, and the available flow rate is 30ml / min

How to choose the best operating conditions of carrier gas in gas chromatography analysis?
1. The nature of the carrier gas has an impact on column efficiency and analysis time;
2. When using a carrier gas with a relatively low molecular weight, the optimal flow rate and minimum tray height are superior to those with a relatively high molecular weight;
3. The use of light carrier gas is beneficial to improve the analysis speed, but the column efficiency is low;
4. It is best to use at low speed, which can not only improve column efficiency, but also reduce noise;
5. In addition, the choice of carrier gas should also be considered from the sensitivity of the detector.

How to choose the best operating condition of gasification chamber temperature in gas chromatography analysis?
1. The temperature of the gasification chamber is controlled to make the sample instantaneously vaporize without causing the sample to decompose to the best.
2. The general rule is that the temperature of the gasification chamber is higher than the boiling point of the sample and the peak height can be quantified by keeping the gasification temperature constant.

In chromatographic analysis, what kind of injectors are used for gas, liquid and solid samples?

Gas sample injection: use a syringe to inject a sample; use a gas quantitative tube to inject a sample, commonly used six-way valve.

Liquid sample injection: micro syringe.

Solid sample injection: After the solid sample is dissolved, the sample is injected with a micro syringe, and the headspace sampling method is used. How to choose the best operating conditions of column temperature in gas chromatography analysis?
1. The column temperature is generally adopted as the average boiling point of the analyte or a little lower;
2. The column temperature cannot be higher than the maximum working temperature of the fixing solution and lower than the sample decomposition temperature;
3. In special cases, the column temperature can be much lower than the column temperature (cyclohexanone in cyclohexanone hydrogen chromatography analysis of cyclohexanone boiling point of more than 160 degrees, with 55 degrees column temperature peak type and peak speed are very good)

How to choose the best operating conditions of column shape, column diameter and column length in gas chromatography analysis?
1. Reducing the diameter of the column is beneficial to increase the efficiency of the column and improve the resolution, but the diameter is too small, which is not conducive to the analysis speed;
2. The greater the difference between the diameter of the column and the radius of curvature of the column, the better;
3. Generally, the length of the packed column is about 2 and the capillary column is about ten or tens of meters. What should be paid attention to when using thermal conductivity detector?
1. The temperature and temperature of the thermal conductivity cell should be higher than or close to the column temperature to prevent sample condensation;
2. The hot wire, in order to avoid the oxidation of the hot wire, it is necessary to pass the carrier gas first, and then the bridge flow. When closing, what are the basic structures of the bridge flow and then the carrier gas heat conduction pool?
1. The thermal conductivity cell detector is made of stainless steel body, cell and thermal element;
2. There are three basic structures: straight-through type; diffusion type; semi-diffusion type.

How to control the temperature of the thermal conductivity detector?
1. The temperature of the thermal conductivity detector needs to be higher than the column temperature to prevent the condensation of the separated substances.
2. More importantly, the accuracy of temperature control can be controlled here. Within 0 and 05.

Briefly describe the performance indicators of the gas chromatography detector?
1. Sensitivity; 2. Sensitivity; 3. Linear range; 4. Stability.

Briefly describe the analysis principle of the thermal conductivity detector?
1. The thermal conductivity detector is based on different substances having different thermal conductivity coefficients.
2. When the sample is not injected, the temperature and resistance of the tungsten wire of the two cell holes are equal.
3. During sample injection, the carrier gas passes through the reference cell, and the carrier gas carries the sample components through the measuring cell. Because the thermal conductivity of the mixed gas composed of the components and the carrier gas is different from that of the carrier gas .
4. Therefore, the temperature of the tungsten wire in the measuring cell changes, so that the resistance values ​​of the two tungsten wires in the two cell holes are different.
5. Measure this difference through the bridge to measure the content of the measured component. What are the precautions for the hydrogen flame detector?
1. The insulation of the ion head is better, and the shell should be grounded;
2. The operating temperature of the hydrogen flame ionization detector should be greater than 100 degrees;
3. The nozzle and collector of the ion head should be cleaned after a certain period of use. The basic principle of hydrogen flame ion detector?
1. The hydrogen flame detector is made according to the principle that flammable organic matter in the chromatographic effluent is ionized in a hydrogen-oxygen flame;
2. Due to the electrostatic field caused by the collector and the emitter near the flame;
3. When the measured component burns to generate ions, it moves directionally under the action of an electric field to form an ion current, which is amplified by a micro-current amplifier and then recorded by a recorder. (At present, there are two basic principles of hydrogen flame ion detector, one is ionization under the action of fire, and the other is ionization under the action of electric field.)

What are the commonly used stationary phases in gas-solid chromatography?
1. Activated carbon; 2. Alumina; 3. Silica gel; 4. Molecular sieve; 5. Polymer porous beads. What is the principle of column fixative selection?
1. The principle of similar compatibility; 2. The principle of using special intermolecular forces; 3. The principle of using mixed fixing liquid. What is a stationary phase? The substances that can not move in the chromatographic column and can play a separation role are called stationary phases.

What are the types of chromatographic stationary phases?
1. One type is the adsorbent porous solid material called adsorbent;
2. One type of liquid substance that can play a role of separation is called a fixed liquid.

What are the commonly used solid adsorption stationary phases?

Commonly used solid adsorption stationary phases are: adsorbent, polymer porous beads, chemically bonded stationary phase.

What are the requirements for gas chromatography to choose a stationary solution?
1. Good thermal stability, low vapor pressure, and liquid state at chromatographic temperature;
2. The sample has sufficient solubility in the fixing solution;
3. High selectivity;
4. It is chemically inert.

What characteristics should the carrier for gas chromatography have?
1. It should have a large specific surface area;
2. It should be chemically inert;
3. Regular shape of carrier;
4. Must have greater mechanical strength.

Briefly describe the pretreatment of the chromatographic column tube?
1. Bend the stainless steel pipe with the required length into the required shape;
2. Wash with 10% hot alkali to remove oil stains and wash with tap water;
3. Wash the metal oxide in the tube with 10% hydrochloric acid;
4. Rinse with water first and then with ethanol, and then dry before use.

How is the carrier of the column coated?
1. Weigh a certain amount of fixing solution according to the ratio and dissolve it in an organic solvent;
2. Add the carrier, the solvent should submerge the carrier and gently stir;
3. Irradiate with infrared light to evaporate the solvent. After the solvent volatilizes, the coating is completed;

How to age the column?
1. At room temperature, connect one end of the column to the vacuum pump to the gasification chamber of the chromatograph and vent the other end;
2. The carrier gas is blown at 0 and 5 at room temperature, so that the air in the column is blown clean;
3. Then increase the temperature and keep 12-24 at a temperature 20-30 degrees higher than the use temperature.
4. Reduce to room temperature, complete aging, and connect the detector.

Why age the column?
1. The newly packed chromatographic column contains residual solvents and a part of low molecular weight substances and other volatile impurities in the fixing solution, so it is aging.
2. Another purpose is to make the fixing solution evenly coated on the carrier.

There are several methods commonly used in chromatographic quantitative analysis?

Internal standard method; external standard method; normalization method.

What is the basis for quantification by gas chromatography?
1. The size of the response signal generated by the detector is proportional to the amount of components entering the detector. Therefore only