Common Faults and Repair Methods of Gas Chromatograph

As an instrument for analysis and detection , 　　gas chromatograph is widely used in the fields of petroleum, chemical industry, biochemistry, medicine and health, food industry, environmental protection, etc. Due to the complex structure, many conditions to set, and long recovery preparation time, various abnormal conditions often occur during the use of the instrument. If these faults are not eliminated and repaired in time, on the one hand, it will cause difficulties in use, and on the other hand, it will also damage the chromatograph. This article will list some common faults of gas chromatographs and introduce solutions to these common faults.

　　1. Failure of no chromatographic peak after injection: The gas chromatograph does not change the detection signal after injection, the instrument does not produce a peak, and the output is still a straight line. When encountering this situation, you should check one by one from the sample injection needle, injection port to the detector.

　　1. First check whether the syringe is blocked. If there is no problem;

　　2. Check whether the graphite gaskets of the injection port and the detector are tight and leak-proof;

　　3. Then check whether the chromatographic column is broken or leaking;

　　4. Finally, observe whether the detector outlet is unobstructed. The unobstructed detector outlet is very important. For example, users may encounter such a problem at work: the instrument worked normally the day before, but there was no response peak signal after turning it on the next day. Check that the injection port, syringe, gasket and chromatographic column are all normal, but there is no peak. It is accidentally found that the injection port column head pressure cannot reach the set value and is always high. At this time, it is suspected that the ECD detector outlet is blocked. Since the ECD emissions have a certain degree of radioactivity, the ECD outlet is led to the outdoors. It was the turn of autumn and winter, and rainwater froze after entering the ECD outlet, causing the outlet of the instrument ECD to be blocked, the column head pressure remained high, the gas could not flow in the gas path, and the sample could not be carried to the detector, so there was no peak.

　　2. Baseline problems: Gas chromatography baseline fluctuation and drift are both baseline problems. Baseline problems can increase measurement errors and sometimes even cause the instrument to fail to work properly.

　　1. When encountering baseline problems, first check whether the instrument conditions have changed and whether the gas cylinder and equipment accessories have been replaced recently;

　　2. If there is a change or the conditions have changed, first check whether the baseline problem is caused by these changes. Generally speaking, such changes are often the cause of baseline problems. Some users have encountered this situation at work: the purity of the new carrier gas is not enough. After the carrier gas is changed, the baseline gradually rises (due to the carrier gas purification tube, the baseline does not change immediately). After turning on the machine the next day, the baseline is very high, accompanied by strong baseline jitter, and all peaks are buried in the noise and cannot be detected. After inspection, the problem occurred in the newly replaced carrier gas. After the carrier gas was replaced, it immediately returned to normal.

　　3. After eliminating the above possible causes of baseline problems, check whether the injection pad is aging (you should develop a good habit of replacing the injection pad regularly);

　　4. Does the quartz wool need to be replaced?

　　5. Is the liner clean? It is worth mentioning that when cleaning the liner, you can first soak it in the solvent that was finally set to volume in the test, then use ultrasonic cleaning for a few minutes, then put it in a high-temperature furnace and heat it to a temperature slightly higher than the working temperature, and finally reinstall it.

　　6. In addition, detector contamination may also cause baseline problems, which can be solved by cleaning or thermal cleaning.

　　3. Faults causing peak loss: There are two reasons for peak loss: one is contamination in the gas path, and the other is that the peaks are not separated.

　　The first situation can be solved by performing multiple dry runs and cleaning the gas lines (inlet, detector, etc.).

　　1. In order to reduce the pollution to the gas path, the following measures can be adopted: there should be a high-temperature cleaning process in the final stage of the programmed temperature rise;

　　2. The sample injected into the injection port should be clean;

　　3. Reduce the use of high-boiling-point oils;

　　4. Use the highest possible injection port temperature, column temperature, and detector temperature.

　　The second situation of peak loss is that the peaks are not separated. In addition to the above reasons, it may also be caused by decreased column efficiency due to system contamination, or due to column aging. However, the peak loss caused by column aging is gradual and slow.

　　False peaks are generally caused by system contamination and air leakage, and the solution is to check for leaks and remove contamination. In daily work, the normal time baseline should be recorded for reference during maintenance.

　　Here are just three common inspection methods for working problems. Gas chromatographs have many fault points and long recovery time. Therefore, the key to equipment maintenance is to correctly analyze the cause. Each time you check a component, you should compare the analysis results before and after to avoid magnifying the problem. I believe that through repeated attempts, you will be able to successfully solve the problem.