Gas Chromatography Machine

Content
1. What is gas chromatography machine?
    1.1 Working principle of gas chromatography machine
2. Components of gas chromatography machine
    2.1 Gas circuit system in gas chromatography machine
    2.2 Injection system in gas chromatography machine
    2.3 Separation system and column temperature chamber in gas chromatography machine
    2.4 Detection system in gas chromatography machine
    2.5 Temperature control system in gas chromatography machine
    2.6 Recording system in gas chromatography machine
3. How to buy gas chromatography machine?

Gas chromatography is a chromatographic separation analysis method using gas as a mobile phase. When the two phases are in relative motion, these substances are repeatedly distributed between the two phases, so that the original only a small difference in nature produces a large effect, and the different components are separated. This method is characterized by high efficiency, high sensitivity, high selectivity, fast analysis, wide application, and easy operation, and is suitable for qualitative and quantitative analysis of volatile organic compounds. Gas chromatography is widely used in the fields of food, environment, pharmaceuticals, biological materials, etc. Gas chromatograph machine is an instrument for qualitative and quantitative analysis of complex multi-component mixtures using chromatographic separation and detection techniques. It can usually be used to analyze organic compounds in soil that is thermally stable and has a boiling point not exceeding 500°C, such as volatile organic compounds, organochlorines, organophosphorus, polycyclic aromatic hydrocarbons, phthalates, etc.

Gas chromatography machine uses a gas as the mobile phase (carrier gas). When the sample is "injected" into the injector by a microinjector, it is carried by the carrier gas into the packed column or capillary column. Due to the difference in distribution or adsorption coefficient between the mobile phase (gas phase) and stationary phase (liquid or solid phase) in the column, the components are separated in the column by repeated distribution between the two phases under the flushing of the carrier gas, and then the components are detected sequentially by the detector connected to the back of the column according to the physicochemical properties of the components.

The signal given by the detector for each component is represented on the recorder as a peak, called a chromatographic peak. The maximum value on the chromatographic peak is the basis for qualitative analysis, while the area encompassed by the peak depends on the content of the corresponding component, so the peak area is the basis for quantitative analysis. A mixture sample is injected and the curve obtained by the recorder is called a chromatogram. Analysis of the chromatogram gives the results of qualitative and quantitative analysis.

Gas chromatograph machine is generally composed of six systems, which are gas circuit system, injection system, separation system (column system), detection system, temperature control system, and data processing system.

The gas circuit system in a gas chromatography machine includes the gas source, purifier, and air circuit control correlator.

Remark: Electrolyte is 100g of potassium hydroxide dissolved in 400mL of pure water.

a. The gas line pressure is recommended to be around 0.4M
pa for carrier gas and auxiliary gas.

b. The gas line should be regularly checked for air leakage.
Check method: you can turn off the instrument on the gas line, open the cylinder pressure reducing valve, close the pressure reducing valve, and check whether the pressure gauge pressure dropped. It drops if there is a gas leak.

c. The rubber seal of the air circuit should be replaced regularly to prevent aging and air leakage.

Injection systems in gas chromatography machines generally include sample injection devices and inlets. Common injection devices include micro-sampling needles, autosamplers, headspace injectors, thermal resolvers, and six-way gas injection valves. The injection needle size is 10μL. Depending on the test item, you can choose different injection needles. The injection needle needs to be checked for cleanliness and smoothness before injection and cleaned and blown dry before use to achieve no residue. The commonly used capillary column inlet has two modes of operation: split (most of them are split) and non-split (trace detection).

The spacer discharge is expelled at a lower temperature than the vaporization temperature, and spacer purging prevents spacer aging.

Capillary columns have a small sample capacity and the injection volume must be very small. Usually, the injection volume needs to be much less than 1 µl to prevent overloading the column.

a) The injection spacer should be replaced periodically. The injection spacer should be replaced at about 100 pins.

b) If the temperature setting for the inlet port is too high, a high temperature-resistant inlet pad should be used.

c) When replacing the sample pad, the instrument should be operated after cooling down and shutting down or before powering on.

d) The heat sink cap should not be tightened too much to prevent clogging of the sample inlet needle.

a) The glass liner of the sample inlet should be replaced or cleaned regularly.

b) In case of frequent use, mandatory replacement should be done once a quarter.

c) When replacing the liner tube, it needs to be ultrasonically cleaned together with the heat sink cap.

d) Before disassembling the instrument, all parts must be brought down to room temperature, disconnect the power supply and turn off the gas supply of each pipeline. Remove the black heat insulation cover, remove the heat sink cap, use a special bayonet wrench to remove the cap connected to the gas line, and carefully remove the liner tube.

e) Debris and unvaporized material from the feed pad can accumulate in the liner tube, leading to the deposition of dirt in the liner tube. Dirty liner tubes can cause such things as changes in peak shape, poor reproducibility, no peaks, or low response values. Before cleaning, you need to remove the O-ring. The glass liner can be ultrasonically cleaned with acetone or ethanol. If there are stubborn stains, you can use 20% nitric acid to soak and clean. You can use chromic acid washing solution to soak and clean according to the degree of cleanliness. Then rinse with a lot of water and then ethanol cleaning and blowing dry for use.

f) In the process of replacing and filling the quartz cotton of the liner, you need to be well protected by wearing latex gloves and a mask. The filling length is about 1cm, and the quartz cotton is filled in the middle of the liner tube at the Y-shaped closing. Take a small amount of quartz cotton spread into a thin layer of 2cm square plane, press the center and push into the corresponding position of the liner tube.

The manifold is connected with a control flow device after the manifold. When used for a long time, there will be high boiling material and other accumulation or blockage of the manifold, so it needs to be cleaned or replaced. After removing the manifold, you need to clean it with a syringe filled with acetone, then blow dry it with nitrogen and reinstall it. Routinely clean every six months. It is recommended to directly replace the cold trap with a new one, and check the status every six months.

The separation system and column temperature chamber in the gas chromatography machine typically include the column chamber (back door, fan, heating), the column, and the associated connectors.

The column is connected to the injector while the column is in the column oven. Its built-in heating and temperature control assembly can adjust the column temperature in place according to the temperature rise program, and precisely control the temperature to assist in the separation of the components of the sample.

When replacing a chromatographic column, the head and tail of the column need to be cut by 1-2 cm. A portion of the column often has to be removed when aging the column as well. The fastening screw and graphite pad must be passed before cutting the column. The requirements for excising the columns are strict and they should not be broken or cut with scissors at will. Professional cutting tools should be used to make the cutting surface of the column flush.

Aging should be performed on new columns, columns with reduced column efficiency, and columns that have not been used for a long time. The temperature generally follows the formula: T(max) ≤ (use temperature MAX + withstand temperature MAX) /2.

Check the column information before aging to prevent irreversible damage caused by setting too high a temperature. In the process of using the programmed temperature rise, the temperature should be slowly increased from the low temperature at a rate of 1-2°C/min to the highest temperature, and then maintained for 6-8 hours. The process takes a low flow rate carrier gas. If the liner has not been replaced for a long time, clean the glass liner and cut off the front end of the column by a few centimeters before aging. When aging the column, do not connect the detector to avoid contamination the detector.

The removed column needs to be protected to avoid contamination or damage to the column. The head and tail of the column should be sealed with a rubber plug and placed in the box where the column belongs. When the instrument is not used for a long period, the column that comes with the machine should also be removed and sealed.

The detection system in gas chromatography machines usually consists of three parts: detection element, amplifier, and digital-to-analog converter.

The components, separated by the column, enter the detector in turn and are converted into the corresponding electrical signals according to their concentration or mass change with time, which are recorded and displayed after amplification to give the chromatogram. The detector commonly used in laboratories is the flame ionization detector (FID), which has a wide range of applications and is suitable for organic detection.

FID principle: The combustion of carbon-containing organics in an H2-Air flame generates fragment ions, which form a stream of ions under the action of an electric field. The components separated by the column are detected according to the intensity of the electrical signal generated by the ion stream.

Tail blow flow rate: Generally, the N2 flow rate is 30; the H2 flow rate is 30; the air flow rate is 300. The optimum ratio can be adjusted according to the instrument. The ignition detector temperature must be greater than 150 ℃, the minimum detection temperature must not be less than 120 ℃.

In gas chromatography determination, temperature control is an important index, which directly affects the separation efficiency of the column, sensitivity, and stability of the detector. The temperature control system mainly refers to the temperature control of the gasification chamber, the column, and the detector.

In the gasification chamber, the temperature control system should ensure instantaneous gasification of the liquid specimen. In the column chamber, the temperature of the separation needs to be accurately controlled. When the sample is complex, the temperature of the separation chamber needs to be controlled according to a certain procedure to ensure that the components are separated at the optimum temperature. In the detector, the separated components must pass through without condensing.

The temperature control mode is divided into the thermostat and programmed temperature rise.

For simple samples with a less wide boiling range, the thermostatic mode can be used. The thermostat mode is used for general gas analysis and simple liquid sample analysis.

Programmed temperature rise means that the temperature of the column changes linearly or non-linearly from low to high temperature during an analysis cycle, so that the components with different boiling points each flow at their optimal column temperature, thus improving the separation effect and shortening the analysis time. For complex samples with a wide boiling range, if it is difficult to achieve good separation at a constant temperature, the programmed temperature rise method should be used.

The recording system in gas chromatography machine is to record the detection signal of the detector for quantitative data processing. Generally, an automatic balance type electronic potentiostat is used to record and plot the chromatogram. Some chromatographs are equipped with an integrator that measures the area of the chromatographic peaks and directly provides accurate data for quantitative analysis. Advanced gas chromatographs are also equipped with electronic computers that can automatically process chromatographic analysis data.

If you are interested in our gas chromatography machine or have any questions, please write an e-mail to [email protected], we will reply to you as soon as possible.