The gas chromatograph (GC) airway system is a closed loop that relies on the stable flow of carrier gas and auxiliary gas to ensure accurate separation and detection of samples. Gas leakage is one of the most common faults in GC operation, which not only affects the stability of the baseline, reduces the accuracy and reproducibility of test results, but also may damage core components such as detectors and chromatographic columns. This article focuses on the leak-prone parts of gas chromatographs, details the detection methods of airway system leakage, and provides standardized operation steps, with a total length of about 1000 words, to help operators effectively identify and handle leakage problems.
Before conducting leakage detection, it is necessary to make adequate preparations: ensure the GC is powered off and the gas source is turned off, release the residual gas in the airway system, and prepare detection tools such as a leak detector, isopropyl alcohol (IPA) and water mixture (leak detection solution), medical syringe, pressure gauge, and wrench. The detection should follow the principle of "from the gas source to the detector, from the outside to the inside, and segmental inspection" to avoid missing leak points and improve detection efficiency.
1. Leak-Prone Parts of Gas Chromatographs
The leak-prone parts of GC airway systems are mainly concentrated in joints, seals, and key components, where the airtightness is easily damaged due to frequent operation, component wear, or improper installation. The specific leak-prone parts are as follows:
First, gas source and pressure regulating parts: including gas cylinder valves, pressure regulators, and connecting hoses between gas cylinders and GCs. These parts are prone to leakage due to loose connections, aging hoses, or damaged pressure regulator seals. Severe leakage here can be accompanied by a hissing sound, which is easy to identify initially.
Second, inlet parts: including inlet gaskets, chromatographic column joints, and ferrule connections. The inlet gasket is frequently used during sample injection, and it is easy to age, crack, or deform after long-term use, resulting in leakage; improper installation of the chromatographic column or loose ferrule can also cause gas leakage at the joint.
Third, detector parts: including detector interfaces, signal lines, and sealing gaskets. Leakage here will lead to unstable detector signals, reduced response value, or even failure to detect peaks. For example, leakage at the FID detector interface will affect the combustion of hydrogen and air, resulting in unstable baseline.
Fourth, pipeline and valve parts: including carrier gas pipelines, auxiliary gas pipelines, and flow control valves. Pipeline blockage or valve internal wear may cause local pressure changes and leakage; long-term use of pipelines may also lead to leakage due to aging and cracking.
2. Common Methods for Detecting Airway System Leakage
There are three main methods for detecting GC airway leakage, which can be selected according to the leakage degree and on-site conditions, ensuring accuracy and avoiding damage to the equipment.
The first method is the leak detection solution method, which is suitable for detecting general leakage and is simple and low-cost. Prepare a mixture of IPA and water (IPA reduces the surface tension of water to facilitate penetration into cracks), and use a medical syringe to drop 1-2 drops of the solution on the suspected leak points (joints, gaskets, valves). If tiny bubbles are continuously generated, it indicates leakage; if no bubbles are generated, the airtightness is good. It should be noted that soapy water is not recommended, as it may be sucked into the airway and contaminate the system; this method is not suitable for hot parts, as the solution will boil quickly and affect the judgment.
The second method is the leak detector method, which is suitable for detecting micro-leakage and hot parts, with high accuracy. Most leak detectors consist of a vacuum pump and a thermistor detector, which can detect the thermal conductivity of leaking gas (such as helium or hydrogen). Turn on the gas source to maintain the system pressure, hold the detector probe close to the suspected leak points, and if the detector display changes significantly, it indicates leakage. This method can be used on hot fittings such as the inlet and detector, but it is affected by air flow, so it should be operated in a windless environment.
The third method is the pressure drop method, which is suitable for overall leakage detection of the airway system. Turn on the gas source, adjust the system pressure to 0.3-0.6MPa, stabilize it for 5 minutes, then close the gas source valve and block the airway outlet. Observe the pressure gauge; if the pressure drops by more than 0.02MPa within half an hour, it indicates system leakage, and then conduct segmental inspection to locate the specific leak point. This method can quickly judge whether there is overall leakage, but it cannot directly locate the leak point, so it needs to be used with other methods.
3. Standard Operation Steps for Leakage Detection
Step 1: Check the gas source part first. Open the gas cylinder valve, adjust the pressure regulator to the rated pressure, and listen for hissing sounds. If there is a sound, use the leak detection solution to check the gas cylinder valve, pressure regulator, and connecting hose, and tighten the loose connections or replace the damaged parts.
Step 2: Check the inlet and chromatographic column joints. Apply the leak detection solution to the inlet gasket, chromatographic column ferrule, and other parts, or use a leak detector to detect. If leakage is found, replace the gasket or ferrule, and reinstall the chromatographic column (avoid over-tightening to prevent column damage).
Step 3: Check the detector part. Focus on the detector interface and sealing gasket, use the leak detection solution or leak detector to detect, and replace the aging gasket if leakage is found.
Step 4: Check the pipeline and valve parts. Conduct segmental inspection of the carrier gas and auxiliary gas pipelines, block one end of the pipeline, apply pressure, and use the leak detection solution to check each joint and valve. If leakage is found, replace the pipeline or valve.
In conclusion, gas leakage is a key factor affecting the normal operation of gas chromatographs. Operators should be familiar with the leak-prone parts, master the correct detection methods, and conduct regular leakage detection, especially after replacing gas cylinders, chromatographic columns, or gaskets. Timely detection and handling of leakage can not only ensure the accuracy of test results but also extend the service life of the equipment. If micro-leakage is difficult to locate, professional maintenance personnel should be contacted to avoid further damage to the system.
