Operating Procedures for Gas Chromatography

Operating Procedures for Gas Chromatography (FID as an Example)

1、 Preparation before the experiment

1. Ensure that the gas chromatograph is in normal working condition, check whether all components of the instrument are intact, and whether the pressure of the gas cylinder meets the requirements.

2. Use gas chromatography columns and detectors that meet the requirements..

2、 Sample processing

1. The preparation of samples should meet the experimental requirements and avoid distortion of experimental results due to improper sample preparation.

2. Sampling should be accurate and avoid contamination or mixing with other samples.

3. Perform necessary purification treatment on the sample, filter it through a microporous membrane to ensure that the sample is a clear solution. Put the processed sample into a suitable liquid chromatography sample bottle for later use. The sample size is generally above 0.5ml to avoid the injection needle being unable to suck the sample. If the sample size is small, an inner liner can be added to the small bottle before loading the sample into the small bottle. ）

4. Confirm that there is liquid in the needle washing bottle on the injector (usually organic solvent). If there is a lack of needle washing liquid, the injection needle is prone to clogging and the sample is prone to residue

3、 Instrument operation stage

1. Open the main valve of the nitrogen cylinder (high-purity nitrogen is required), confirm that the nitrogen pressure is around 0.4Mpa, and turn on the power switches of the hydrogen and air generators (the gas generator has been adjusted before leaving the factory and does not need to be adjusted).

2. Turn on the power switch of the chromatograph, wait for the gas phase instrument to complete self-test, then open the corresponding workstation software on the computer and connect the gas phase.

3. Call the sample testing method, and the parameters will be downloaded to the instrument. After downloading the parameters, confirm whether the injection port temperature, pressure, column temperature, and detector parameters have reached the set values. If the pressure at the injection port does not meet the requirements, it may be due to air leakage at the injection port, and it may be necessary to replace the spacer, O-ring, etc

4. Ignition: Wait for the detector temperature and hydrogen, air, and tail air to reach the method set values. The instrument will automatically ignite, and during normal ignition, a "beep" explosion sound will be heard. After successful ignition, a bright metal plate (such as a bright wrench) can be used to approach the detector outlet. When the ignition is truly ignited, obvious water vapor will be seen on the metal plate. The normal signal value should be less than 20PA. If the baseline signal value is too high, the gas may be impure or the detector may be dirty and require maintenance. In addition, if the ignition fails, it is necessary to investigate the cause of the ignition failure (such as insufficient gas flow, short circuit of the ignition coil, etc.)

5. Operation and monitoring phase

1. Running sequence: Based on the edited injection sequence table, run the sequence method to analyze the sample. (Add one quality control sample after 10-15 samples, and use the recovery rate to determine if the instrument is functioning properly)

6. Data analysis and processing stage

1. Integral chromatographic peak: Integrate the chromatographic peaks in the chromatogram to obtain the peak area.

2. Quantitative calculation: According to experimental needs, different methods are used for quantitative calculation, such as external standard method, internal standard method, area percentage method, etc.

7. Shutdown procedure: Extinguish the hydrogen flame detector, turn off the hydrogen and air sources, and set the initial temperature of the column box, detector temperature, and injector temperature to low temperature (60 ℃) after the hydrogen flame is extinguished. After the temperature drops to the set temperature, turn off the power of the chromatograph. Finally, turn off the nitrogen gas.