What are the good habits of gas chromatography for routine maintenance?

1. Operate according to the procedures of the instrument manual.

This is mainly for the newly purchased and installed gas chromatograph. It is necessary to check whether the parts and spare parts are complete, and whether the instructions are complete. Be sure to keep these materials in a safe place for future reference. Before operating the instrument independently, be sure to read the instruction manual carefully and operate it in strict accordance with the regulations. This is a precursor to instrumental analysis and is easy to communicate with the manufacturer when problems occur with the instrument. Especially for instruments that are still under warranty, if the fault or damage caused by improper operation, the manufacturer will not repair it for free, and sometimes the cost is quite objective.

2 , prepare a test sample for the column

The key to ensuring analytical results when performing column performance. For the newly purchased column, the test sample should first be used to evaluate its performance. If the test conditions provided by the column manufacturer are used and the result is unqualified, the return can be requested to avoid the problem of subsequent experiments. More importantly, the performance of the column changes during the subsequent use. When there is a problem with the analysis result, the column can be tested with the test sample and compared with the previous results, which helps to troubleshoot the problem to determine The problem is caused by the column. Each test result should be saved as a column life record. In addition, after a period of testing, the column should be subjected to a high temperature aging to remove any contaminants that may remain in the column, and then the column is re-evaluated using the test sample.

3 , timely replacement of capillary column seals

Leakage of graphite gaskets is one of the common faults in gas chromatography. The same gasket must not be reused on different columns. Even if the same column is removed and reinstalled, it is best to replace it with a new one to ensure higher efficiency. If the leak is found after installing the column and replacing the gasket, it will waste more time. Even if the seal can be used, it needs to be tightened more than the new one, and it is easy to twist the column.

4 , use the purity of the gas meets the requirements

The carrier gas must be of high purity to avoid interference with analysis and contamination of the column or detector. After all, the price of the column is more than ten times that of high-purity nitrogen or helium. If you use ordinary gas because of saving money, it will not be worth the loss. The auxiliary gas of the detector is preferably also of high purity grade. Although ordinary gas can be used when the sensitivity is not high, the cost is likely to cause detector contamination.

5 , regular replacement of gas purifier packing

The color-changing silica gel can judge its performance according to the color, but a purifier that adsorbs organic substances such as molecular sieves is not judged by observation. Therefore, it is best to replace it regularly, basically in a three-month cycle. If the silica gel is packed with molecular sieves, the molecular sieve should also be replaced when replacing the silica gel.

6 , using reliable pressure regulating valve

The pressure reducing valve installed on the gas cylinder is to ensure the quality. Some new valves will leak, so you need to check leaks frequently and find problems at any time. If you do not pay attention to the light, it will cause waste of gas, and then there will be safety problems, and the consequences will be disastrous.

7. Regularly change the inlet septum

Leakage of the inlet septum is one of the common faults in gas chromatography. Some instruments have self-checking function to detect air leaks, but some tiny leaks are not guaranteed. Some instruments have no self-test function, and air leaks are even more difficult to check. Beginners who used to have GC-MS leaked a bottle of helium overnight and had some silicon-containing ion peaks on the spectrum. Checking all the pipelines and connecting valves did not find any problems. Finally, it was found that the inlet septum was used for too long, and there was a light-transmitting hole in the middle, and the helium gas leaked from here. In addition, the aging degradation of the septum can also cause interference in the analysis results. For example, the spacer debris will fall into the vaporization chamber to cause the appearance of ghost peaks, as described above for the silicon-containing ion peak.

Commercially available septa are generally divided into three types, normal (temperature to 200 ° C), high quality (temperature to 300 ° C) and high temperature (temperature to 400 ° C). The better the high temperature resistance or aging resistance, the longer the life, and the higher the price. When selecting, it can be determined according to the actual analysis conditions and requirements. The conventional analytical laboratory (vaporization temperature does not exceed 300 °C) can choose high-quality septum. It is best to select high-temperature septum when doing high-temperature gas phase analysis. As for how often to replace the septum, it is necessary to look at the nature and analytical conditions of the sample. Conventional testing laboratories typically change one per day. The continuous use time of a septum should not exceed one week. Of course, for experienced "old drivers", it is possible to judge whether it needs to be replaced by experience or feel.

8 , timely cleaning the syringe

A clean syringe prevents interference with sample memory effects. The sample needs to be cleaned when the sample is replaced. When the sample is injected multiple times with the same sample, the sample itself is also used to clean the syringe. When a syringe is temporarily not in use (such as during a holiday), it must be thoroughly cleaned, otherwise the sample remaining in it may stick the core and cause the syringe to be scrapped. Also be aware of this issue when using the autosampler. It is best to replace and clean the syringe frequently.

9. Regularly inspect and clean the inlet liner

After long-term use, the instrument will find tar-like substances in the liner, which is caused by non-volatile components in the sample. In addition, there will be particulate matter accumulation (separator debris, solid matter in the sample), which will interfere with the normal conduct of the analysis. Therefore, it is necessary to check regularly and clean it in time. It is worth noting that the current liner has been filled with some silanized quartz glass wool, which can improve the vaporization efficiency of the sample and prevent the block debris from entering the column and causing blockage, or according to actual needs. Replace or increase or decrease the glass wool to achieve better results.

10 , retain the complete instrument usage record

The instrument usage record is the history of the instrument and should be recorded on a daily basis, including the operator, analysis samples, conditions, instrument working status, etc. Once the instrument has problems, this is an important information for finding the cause. Some research laboratories often pay less attention to the filling of instrument usage records, which is a problem that needs attention.

11 , replacement parts must be carried out one by one

When repairing the instrument, do not replace multiple parts at a time, which is easy to make a judgment error. One part should be replaced at a time, and the other should be replaced after testing. This will allow you to more accurately determine the cause of the failure and avoid unnecessary expenses.

(Content source Hengtianli Instrument Network)