How to use a gas chromatograph? Gas chromatographs are widely used in industrial gas detection and are very practical gas detection devices. However, due to their high precision and relatively complex operation, they require a very strict testing procedure. This article uses the YTC450 gas chromatograph as an example to briefly introduce how to use a gas chromatograph.
After the instrument is correctly installed, debug the instrument according to the following steps to confirm that it is in good condition.
I. Startup Procedure
① First, open the main valve of the nitrogen cylinder and adjust the pressure reducing valve to 0.3~0.4 MPa. Adjust the column inlet pressure to approximately 0.04 MPa.
② Turn on the power switch on the rear side of the GC gas chromatograph. When the main screen appears, set the test parameters (column temperature, injector temperature, detector temperature, etc.). When setting the column temperature, be sure to pay attention to the maximum operating temperature of the column.
③ When the temperature reaches the set value, turn on air and hydrogen. Open the main valves of the air and hydrogen cylinders and adjust the pressure reducing valves to 0.3~0.4 MPa.
④ Open the needle valve switches for air and hydrogen on the instrument panel. (Reference values: air 7 turns, hydrogen 4 turns.)
⑤ Ignite with the igniter. Note: open the hydrogen needle valve to more than 5 turns for ignition, then turn it back to 4 turns after the flame is lit. To prevent water accumulation, ignite only when the detector temperature is greater than 150°C and the outside of the detector is slightly warm. After ignition, water vapor appears above the detector, and the signal shows a surge.
⑥ Open the workstation and check the baseline. After stabilizing for about 30 minutes, once the GC temperature reaches the set value and the baseline is stable, measurement can be performed.
II. Setting Test Conditions:
The chromatographic conditions should be set by selecting the appropriate column based on the different properties of the compounds. Generally, polar compounds use polar columns, and non-polar compounds use non-polar columns. The column temperature is mainly determined by the complexity of the sample, with the goal of completely separating each compound component in the shortest time. For mixtures, programmed temperature rise is generally used. The column temperature setting should take into account both high and low boiling point or melting point compounds.
Generally, there are two testing methods for compounds:
① Capillary column split method: The sample is directly introduced into the chromatographic column without dilution, and the injection volume should be less than 0.1 μl. If it is a solid compound, dilute it with as little solvent as possible, and the injection volume is 0.2~0.4 μl.
② Large-bore capillary column splitless method:
Whether solid or liquid, it must be diluted before injection. The injection volume is 0.2~0.4 μl (1 ml/mg).
III. Precautions:
① The detector temperature must not be lower than the injector temperature, otherwise the detector will be contaminated. The injector temperature should be higher than the maximum column temperature, and the compound should not decompose at this temperature.
② Compounds containing acids, bases, salts, water, or metal ions cannot be analyzed directly; they must be treated before analysis.
③ The sample taken by the injector should avoid air bubbles to ensure injection reproducibility.
④ Before sampling, rinse the syringe repeatedly with solvent, and then rinse at least 2-5 times with the sample to be analyzed to avoid cross-contamination between samples.
