As we all know, gas chromatography is a technical means for separation and analysis of gas. If there is a problem in the gas chromatography system, the gas leakage will have a great impact on the detection results and the system itself. Today we will talk about the gas phase. What should I do if the chromatogram leaks?
First of all, we need to know what changes in the gas chromatogram are precursors to air leaks?
Air leakage is divided into carrier gas leakage and auxiliary air leakage.
When the carrier gas leaks, the chromatogram has the following changes:
1 Baseline change
a. The baseline is unstable (noisy, irregular fluctuations during constant temperature operation or drifting in one direction). i. The baseline noise is large, which may be due to excessive carrier gas flow rate or air leakage; ii. Baseline sine wave fluctuation, which may be unstable carrier gas flow, in addition to checking the gas source, it is also necessary to exclude air leakage; iii. Constant temperature operation When the baseline randomly fluctuates or drifts in one direction, these phenomena can first rule out whether the carrier gas leaks.
b. The baseline cannot be zeroed. The thermal conductivity cell detector may be leaking, causing the thermal wire to not completely bubble into the hydrogen, and the thermal wire is out of balance or has been burned out.
1 Baseline change
a. The baseline is unstable (noisy, irregular fluctuations during constant temperature operation or drifting in one direction). i. The baseline noise is large, which may be due to excessive carrier gas flow rate or air leakage; ii. Baseline sine wave fluctuation, which may be unstable carrier gas flow, in addition to checking the gas source, it is also necessary to exclude air leakage; iii. Constant temperature operation When the baseline randomly fluctuates or drifts in one direction, these phenomena can first rule out whether the carrier gas leaks.
b. The baseline cannot be zeroed. The thermal conductivity cell detector may be leaking, causing the thermal wire to not completely bubble into the hydrogen, and the thermal wire is out of balance or has been burned out.
2 Peak change
a. The peak shape becomes smaller, the retention time is normal, the carrier gas leaks after the column or the sampler, and the silica gel pad leaks during the injection;
b. The peak shape becomes smaller, the retention time becomes larger, there is a leak in the gas path from the injector to the detector, or the injection pad continuously leaks.
a. The peak shape becomes smaller, the retention time is normal, the carrier gas leaks after the column or the sampler, and the silica gel pad leaks during the injection;
b. The peak shape becomes smaller, the retention time becomes larger, there is a leak in the gas path from the injector to the detector, or the injection pad continuously leaks.
3 Under the premise of eliminating the injection technique, the reproducibility of multiple injections (retention time, peak area and quantitative results).
When assisting gas leakage, it generally shows a decrease in peak response or even no response. For example, when the hydrogen flame ionization detector (FID) is operated, the hydrogen source and the air source are out of control and the flow is unstable, which may cause irregular fluctuations in the baseline during constant temperature operation.
Then it’s leak detection, and it’s the most important part.
Gas leaks can cause the instrument to malfunction, unstable retention time, and changes in chromatographic response. Gas path leakage, divided into carrier gas leakage or auxiliary gas leakage, mainly in the following aspects:
1 The carrier gas flow rate is not normal, such as a. The flow rate is too small to adjust, b. The flow rate is too small to adjust, c. The flow rate is unstable after adjustment.
2 Auxiliary gas leakage, such as hydrogen flame ionization detector, is shown in: a. The hydrogen flame detector does not catch fire, b. The constant temperature fluctuation occurs at the baseline.
When the instrument is not working properly, or if the gas leakage is suspected by the phenomenon on the chromatogram (see Question 6), the leak point should be found and maintained. In order to quickly detect leaks, it should be combined with leak detection due to the situation of air leakage.
1 When the flow rate of the carrier gas is abnormal.
a. The flow is too large to adjust, it may be: i. There is leakage in the gas path after the flow control valve; ii. The flow control valve is damaged.
b. When the flow rate is too small, i. If you hear obvious air leakage, check for leaks in the sound; ii. No obvious air leakage, the pressure of the high pressure valve of the cylinder is normal, such as the cylinder front pressure is too low and the cylinder If the low pressure cannot be adjusted normally, it means that the pressure reducing valve is broken or leaking. In other cases, the air circuit is blocked.
c. After the flow adjustment is unstable, under the premise of normal cylinder pressure and normal column temperature, it may be: i. air leakage in front of the gas path valve; ii. air leakage inside the air valve.
a. The flow is too large to adjust, it may be: i. There is leakage in the gas path after the flow control valve; ii. The flow control valve is damaged.
b. When the flow rate is too small, i. If you hear obvious air leakage, check for leaks in the sound; ii. No obvious air leakage, the pressure of the high pressure valve of the cylinder is normal, such as the cylinder front pressure is too low and the cylinder If the low pressure cannot be adjusted normally, it means that the pressure reducing valve is broken or leaking. In other cases, the air circuit is blocked.
c. After the flow adjustment is unstable, under the premise of normal cylinder pressure and normal column temperature, it may be: i. air leakage in front of the gas path valve; ii. air leakage inside the air valve.
2 The auxiliary gas is not normal.
If the hydrogen flame detector (FID) does not catch fire, the simplest reason may be improper ratio of nitrogen, hydrogen and air or hydrogen leak. If the flow rate is not normal (the flow rate is too small, the volume is too small, or the flow is unstable), please refer to the place where the gas path leaks. Most of them are at the gas line joint. When the joint is aligned, when the joint is assembled There are several situations that can cause air leaks:
a. There is dirt in the joint tightness;
b. joint gasket is not suitable;
c. Without tightening, on the basis of ensuring the above situation is correct, first connect the joints by hand and then tighten them a little (not the tighter the better, the gaskets of different materials and the joints of different positions are different. See the instrument manual);
If the hydrogen flame detector (FID) does not catch fire, the simplest reason may be improper ratio of nitrogen, hydrogen and air or hydrogen leak. If the flow rate is not normal (the flow rate is too small, the volume is too small, or the flow is unstable), please refer to the place where the gas path leaks. Most of them are at the gas line joint. When the joint is aligned, when the joint is assembled There are several situations that can cause air leaks:
a. There is dirt in the joint tightness;
b. joint gasket is not suitable;
c. Without tightening, on the basis of ensuring the above situation is correct, first connect the joints by hand and then tighten them a little (not the tighter the better, the gaskets of different materials and the joints of different positions are different. See the instrument manual);
In addition, the internal valve parts are loose, detached or contaminated, which often leads to air leakage; in general, there are fewer air leakage problems in the middle of the gas path, and occasionally the pipeline breaks and leaks.
According to the degree of air leakage, the method of detecting air leakage can be divided into:
i. Severe air leaks. When the gas source is turned on and stabilized, a clear leaking sound is heard, such as a silky sound, indicating a large leak in the gas path. At this point, the flow rate of the flow path should be widened, and the leak should be checked with soapy water near the pipe joint where the air leakage sound appears.
Ii. General air leaks. Block the gas path outlet, observe the rotor flow meter in the gas path, the rotor can slowly drop to zero, then there is no air leakage, otherwise it will leak. Or observe the system pressure gauge, open the gas source, adjust the output pressure between 0.3-0.6MPa, wait for the gas path to stabilize, block the gas path outlet, and then close the gas source main valve, if the pressure gauge has a significant drop within half an hour , indicating that this part of the leak.
Specific detection of leaking parts should be detected in stages and gradually leaked. If the gas source is screened between the gas source and the rotameter or pressure gauge, refer to the above method to block the rotor flowmeter or pressure gauge outlet. The rotor does not fall to zero or the pressure gauge drops. Then use soapy water to check for leaks. . For some small precision parts such as detectors, it can block the outlet and pressurize the airflow, soak in the ethanol, and there is a leak in the bubble.
Finally, attach the most recent experimental experience: When using a gas chromatography mass spectrometer, when the spectral search results are abnormal, the tuning and leak detection can be re-examined, most likely due to air leakage.
Single use only.
Imported IC can have an accurate result.
Model: Adult, Enfant, Infant, Newborn.
Certification: CE, ISO
Adult breathable film type
Adult non-woven type
Adult sponge type
Infant breathable film type
Infant non-woven type
Infant sponge type
Pediatric non-woven type
Infant foam package type
Pediatric foam type
Pediatric non-woven type
Adult foam type
Pediatric foam type
SPO2 Sensor,Disposable Fingertip SPO2 Sensor,Fingertip SPO2 Sensor,Adult Fingertip Pulse Sensor
Zhejiang Haisheng Medical Device Co., Ltd , https://www.hisernmedical.com