Precautions for operating headspace injector of gas chromatograph
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Precautions for operating headspace injector of gas chromatograph

source:中仪宇盛   date:2022-04-24 11:19:19   click:
  


From the beginning of 2020 to now, the epidemic has been repeated and never stopped. Every time we relax a little, the virus will jump out to remind us that we may have to accompany masks for a long time in the future. Wearing masks is one of the key means to block the spread of the epidemic. As an important commodity for epidemic prevention and control, the quality of masks is particularly important.

Recently, Hebei consumer rights and Interests Protection Commission, Beijing Consumer Association and Tianjin Consumer Association jointly carried out a comparative test of epidemic masks. As an ordinary consumer, the staff randomly purchased 20 samples from offline pharmacies in four districts and cities, including 14 medical surgical masks and 6 disposable medical masks. Hebei Pharmaceutical and medical device inspection and Research Institute is entrusted to carry out the test according to the standards of medical surgical mask (yy0469-2011) and disposable medical mask (YY / 0969-2013). It mainly detects five important indicators, such as mask belt, ethylene oxide residue, bacterial filtration and microorganism. Among them, ethylene oxide residue was detected for sterilized masks and microbial indicators were detected for non sterilized masks. The results showed that the five important technical indexes detected in 20 samples met the standard requirements.

◀  Mask, why is there ethylene oxide? ▶

The mask is in direct contact with the respiratory system of the human body. Why is there ethylene oxide? Disposable medical masks need to be disinfected before leaving the factory. Disposable medical masks generally have three layers of non-woven fabrics. Fragile non-woven fabrics generally do not adopt high-temperature disinfection method, but use ethylene oxide to kill bacteria, molds and fungi. The disinfection method of industrial production of traditional Chinese medicine masks is to place them in an ethylene oxide disinfection room with a concentration of 400mg / L. after disinfection, they need to stand for 7 days for analysis. They can only be packaged and delivered after the residual amount of ethylene oxide is lower than the required value.

◀  What is ethylene oxide? ▶

Ethylene oxide is a broad-spectrum sterilizing agent with chemical formula of C2H4O and English name of ethylene oxide, abbreviated as EO. It is indeed a toxic carcinogen, which can be used to make fungicides. It is widely used in washing, pharmaceutical, printing and dyeing and other industries. However, it has the characteristics of "Volatile"! When disposable medical masks that meet the requirements leave the factory, the residual amount of ethylene oxide shall not be greater than 10% μ G / g, at this concentration, it will not cause harm to human body.

◀  Detection method of ethylene oxide ▶

The national standard stipulates that extraction method is used for pretreatment, and then gas chromatography is used for quantitative analysis. There are two kinds of extraction methods, one is simulated extraction method (standard method), and the other is limit extraction method. Because the limit extraction method can determine all residues on the instrument, if the limit extraction method meets the limit requirements, it is not necessary to simulate the extraction method. Of course, the more convenient method is to directly inject the sample without using the headspace method of extraction method, which can easily and quickly determine all EO residues on the sample.

Headspace injection is suitable for compounds with low boiling point, not easy to decompose and good volatility. It has clean peak and less interference. It is better for substances that are not easy to extract with solvents. There are the following precautions for the operation of gas chromatograph headspace injector:

NO.1

Since the carrier gas entering the headspace enters the GC at the same time, the gas used in the headspace should also be purified.

NO.2

The heating temperature of headspace bottle, the temperature of quantitative tube and the temperature of transmission line shall be from small to large, and the temperature of transmission line shall be less than or equal to the temperature of injection port.

NO.3

The temperature should not be set too high to avoid damaging the headspace instrument and shortening the service life. The non-volatile or non-volatile samples should not be measured by headspace method.

NO.4

Since the headspace instrument needs to be used together with the gas chromatograph, it is necessary to pay attention to the mutual unification of the parameters of the headspace instrument and the gas chromatograph. For example, the temperature of the vaporization chamber of the gas chromatograph should be higher than the temperature of the transmission line to facilitate the vaporization of the sample.

NO.5

When using headspace, the total flow of GC gas should be the gas flow in headspace plus the flow of GC gas. When calculating the split ratio, it should be noted that it can be calculated after being measured by flowmeter.

NO.6

In the time setting, the time for the sample to fill the quantitative tube should be sufficient, the balance time of the quantitative tube should not be too long, and the injection time should be long enough.

NO.7

If the pressure regulation of the headspace sampler is manual, the sample pressurization and carrier gas pressure shall be recorded after the method is established, so as to avoid the pressure change caused by misoperation, resulting in the error of peak time and the failure of normal detection.

Headspace sampler is a tool to introduce volatiles in liquid or solid into gas chromatography. It realizes sample injection by taking a certain repeatable volume of sample in headspace and injecting it into the carrier gas of gas chromatography. This analysis technology is called "static headspace gas chromatography". "Headspace" refers to the space above the liquid or solid sample in the closed bottle. "Static" refers to the equilibrium state of the volatile in this space, which can be reached only after heating for a certain time. The specific heating temperature and duration need to be determined according to the nature and concentration of the sample.

Headspace sampler is a convenient and fast sample pretreatment method in gas chromatography. Its principle is to put the sample to be tested into a closed container, volatilize the volatile components from the sample matrix through heating and heating, reach equilibrium in the gas-liquid (or gas-solid) two phases, and directly extract the top gas for chromatographic analysis, so as to test the composition and content of volatile components in the sample.

The use of headspace injection technology can avoid the tedious sample pretreatment process, avoid the interference of organic solvents on the analysis, and reduce the pollution to the chromatographic column and injection port.

The full-automatic headspace sampler produced by Beijing Zhongyi Yusheng Technology Co., Ltd. has the characteristics of more convenient operation, stable data and reliable results. It has the function of automatically cleaning the back blowing pipeline and avoiding cross pollution. It can be connected with GC of domestic and foreign brands and models. The sales volume of the instrument has reached new highs!


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