Abnormal conditions and maintenance methods of gas chromatographs in application

2018-11-09 08:13

Due to the complicated structure, many conditions, and long recovery preparation time, gas chromatographs often have various abnormalities during use. Failure to maintain for the cause can have serious consequences. The following Nanjing Kejie instrument introduces the abnormal situation and maintenance of the gas chromatograph in the application.

First, there is no peak after injection

The gas chromatograph did not change the detection signal after the injection, the instrument did not show a peak, and the output was still straight. In this case, check one by one from the sample syringe, the inlet to the detector. First check if the syringe is clogged. If there is no problem, check whether the graphite gasket of the inlet and detector is tight and airtight. Then check the column for leaks and finally check whether the detector outlet is unblocked. The smooth flow of the detector exit is very important. Some people will encounter such problems at work: the previous day, the instrument work is still normal, and there is no response peak signal after the next day. Check inlet, syringe, washer

And the column is normal, but there is no peak, unintentionally found that the inlet pressure of the inlet is not up to the set value, always high, then it is suspected that the ECD tester outlet is not smooth. Since the emissions of E C D have a certain amount of radioactivity, the E C D outlet is led to the outside. At that time, it was the turn of autumn and winter. After the rainwater entered the ECD discharge port, it was frozen. As a result, the ECD exit of the instrument was blocked, the stigma was high, and the gas could not flow in the gas path, so it could not carry the sample to the detector, so it was not. Out of the peak.

In this case, as long as the ECD discharge pipe is immersed in hot water, the problem can be solved after the ice melts.

Second, the baseline problem

Gas chromatographic baseline fluctuations and drifts are baseline problems, and baseline problems can increase measurement errors and sometimes even cause the instrument to fail to function properly. When encountering a baseline problem, you should first check whether the instrument conditions have changed, whether it is a new gas cylinder and equipment accessories. If there is a change or a change in conditions, it is important to check whether the baseline problem is caused by these changes. In general, this change is often the cause of the baseline problem. Some people have encountered this situation at work: the new carrier gas is not pure enough, and after changing the overload gas, the baseline gradually rises (the baseline is not immediately changed due to the carrier gas purification tube). After the next day, the baseline was very high with strong baseline jitter and all peaks were noisy and could not be detected. After inspection, the problem occurred on the newly exchanged carrier gas, and immediately after the replacement of the carrier gas, it returned to normal.

When the above reasons that may cause the baseline problem are ruled out, you should check whether the injection pad is aging (it should be a good habit to change the injection pad regularly); whether the quartz wool should be replaced; whether the liner is clean. It is worth mentioning that when cleaning the liner, it can be fully soaked with the solvent of the final volume of the test, then ultrasonically cleaned for a few minutes, then placed in a high temperature furnace to a temperature slightly higher than the working temperature, and then re-installed. In addition, detector contamination can also cause baseline problems that can be addressed by cleaning or hot cleaning.

Third, the peak is lost, the false peak

There are two reasons for peak loss:

1. There is pollution in the gas path

This can be solved by multiple air runs and cleaning air lines (inlet, detector, etc.). In order to reduce the pollution of the gas path, the following measures can be taken: the final stage of temperature programming should have a high temperature cleaning process; the sample injected into the inlet should be clean; reduce the use of high boiling oils; use the highest possible Sample temperature, column temperature, and detector temperature.

2. The peaks are not separated.

In addition to the above reasons, it may also be caused by a decrease in column efficiency due to system contamination, or due to aging of the column, but the peak loss caused by column aging is gradual and slow.

False peaks are generally caused by system contamination and air leaks, and their solutions are also addressed by checking for leaks and removing contamination. The normal baseline should be recorded during normal work for reference during maintenance.

The above describes only the maintenance methods of the three common problems in the work. The gas chromatograph has more fault points and longer fault recovery time. Therefore, the key to equipment maintenance is the correct analysis of the causes. Hunan Chuangte reminds users that every time a component is inspected, it is necessary to compare the analysis results before and after, so as not to enlarge the problem. I believe that through repeated trials, the problem will be solved successfully.