Abstract: Due to the complex structure, multiple condition settings, and long recovery preparation time, gas chromatographs often have various abnormal conditions during use. If you do not maintain for the cause, it will cause serious consequences.
1. Failure of no chromatographic peak after injection: The gas chromatograph has no change in the detection signal after injection, the instrument does not output a peak, and the output is still a straight line. When encountering such a situation, it should be checked one by one in the order from sample injector, sample inlet to detector.
1. First check whether the syringe is blocked, if there is no problem,
2. Check if the graphite gasket of the inlet and detector is tight and airtight,
3. Then check whether the chromatographic column is broken or leaking,
4. Finally, observe whether the outlet of the detector is unblocked.
5. The smoothness of the detector outlet is very important. Some people will encounter such problems in their work: the instrument was working normally the day before, but there was no response to the peak signal after the next day. Check that the inlet, syringe, gasket, and chromatographic column are normal, but there is no peak, and the column head pressure of the inlet is accidentally found to be below the set value, and it is always too high. At this time, it is suspected that the ECD detector outlet is not Unblocked. Because ECD emissions are radioactive, ECD outlets are led outdoors. At the turn of autumn and winter, the rain water froze after entering the E CD outlet, so the outlet of the instrument E CD was blocked, the column head pressure remained high, the gas could not flow in the gas path, and the sample could not be loaded to the detector. So there is no peak.
Second, the baseline problem: baseline fluctuations and drifts in the gas chromatographic baseline are baseline problems. The baseline problem can increase the measurement error, and sometimes even cause the instrument to not be used normally.
1. When encountering baseline problems, you should first check whether the instrument conditions have changed, and whether there are new gas exchange cylinders and equipment accessories in the near future.
2. If there are replacements or changes in conditions, first check whether the baseline problem is caused by these changes. Generally speaking, this change is often the cause of the baseline problem. Some people have encountered this situation at work: the purity of the new carrier gas is not enough. After the overload gas is replaced, the baseline gradually increases (due to the carrier gas purification tube, the baseline does not change immediately). After starting up the next day, the baseline was very high, with strong baseline jitter. All peaks were obscured by the noise and could not be detected. After inspection, the problem occurred with the newly changed carrier gas. After the carrier gas was replaced again, it returned to normal immediately.
3. When the above causes that may cause the baseline problem are excluded, you should check whether the sample pad is aging (you should develop a good habit of regularly replacing the sample pad);
4. Should quartz wool be replaced?
5. Whether the liner is clean. It is worth mentioning that when cleaning the liner, you can first fully soak it with the solvent of the final volume of the test, then clean it with ultrasonic waves 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 then reinstall it.
6. In addition, contamination of the detector may also cause baseline problems, which can be solved by cleaning or thermal cleaning.
3. Failures that cause peak loss: There are two reasons for peak loss: one is contamination in the gas path, and the other may be that the peaks are not separated.
(1) The first situation can be solved by multiple air runs and cleaning the gas path (inlet, detector, etc.).
1. In order to reduce the pollution to the gas path, the following measures can be adopted: the final stage of the program temperature increase should have a high temperature cleaning process;
2. The sample injected into the inlet should be clean;
3. Reduce the use of high boiling oils;
4. Use the highest possible inlet temperature, column temperature, and detector temperature.
(2) The second case of peak loss is that the peaks are not separated. In addition to the above reasons, it may also be caused by the decrease in column efficiency due to system contamination, or due to column aging, but the peak caused by column aging Loss is gradual and slow.
The false peak is generally caused by system pollution and air leakage, and its solution is also solved by checking the air leakage and removing the pollution. The normal baseline should be recorded in normal work, so as to make reference during maintenance.
Here are only three troubleshooting methods for common problems in the work. There are many failure points of the gas chromatograph, and the failure recovery time is also long. Therefore, the key to equipment maintenance is correct analysis of the cause. Every time a component is checked, the results of the analysis before and after should be compared, so that the problem is not enlarged. I believe that through repeated attempts, the problem will be successfully solved.
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