Recently, a cooperation group led by He Yujian, a professor of the College of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, and Zhongwei Ke, a researcher of the China Institute of Inspection and Quarantine, has developed a new technology for the detection of waste oil, as long as the oil is first made into a nuclear magnetic resonance. Can make the original shape of the trench oil exposed. The relevant research results were published in the first issue of the 2013 China Science: Chemistry magazine.
To judge the quality of oil by molecular nature
"When we talk about NMR, people think of nuclear magnetic resonance examinations in hospitals. In fact, this technology is more widely used in the chemical industry." He Yujian told reporters that hydrogen atoms in cooking oil molecules will undergo chemical shifts in strong magnetic fields. Hydrogen atoms have different degrees of displacement in different molecular environments. Therefore, the composition of edible oil can be judged according to the difference in the chemical shift spectrum of hydrogen atoms after nuclear magnetic resonance.
It is understood that the chemical nature of edible oils is triglycerides, that is, with glycerol molecules as the backbone, three fatty acids are linked by ester bonds. The difference in the state of fatty acids in triglycerides is one of the major differences between edible oil and cooking oil.
“The main nutritional value of edible oil lies in the type and degree of unsaturation of fatty acids. If the chemical bonds break during production and use, the degree of unsaturation decreases and a polymer is produced, it indicates a decline in the quality of the oil.†said He Yujian. This is an important basis for judging the quality of oil.
This technique for identifying waste oils by analyzing the internal structural information of fat molecules has not been common before.
Dr. Cai Botai, a doctoral student in the research group, said that some researchers have used gas chromatography and liquid chromatography to determine whether oil has been used by detecting whether the oil contains high temperatures, high-fried polymers, or foreign substances. “These methods are to first define the next generation of waste oil, and list its characteristics. Then the oil with these characteristics is waste oil. This will often make a lot of types of complex, even work of 'fine' waste oil become 'net fish' ."
12 indicators missing out
“We have performed NMR measurements on more than 60 edible oils and waste oils separately, and then established a map library.†He Yujian stated that a total of 12 differences were found by comparing the relative nuclear magnetic chemical spectrum data of normal edible oil and waste oil. Larger places can be identified.
"We use NMR to detect whether the chemical structure of the oil is complete and correct. With this method, as long as the oil molecule structure is complete, the saturation is in line with the standard and there is no impurity peak, it is good oil, otherwise it is bad oil." He Yujian told reporters.
"When doing sample testing, these 12 indicators sometimes appear contradictory, that is, some indicators show that the oil tested is a good oil, while others show that it may be a waste oil." Cai Bo said too, when this happens, Multivariate data processing methods can help to make "more scientific, more just, and more reliable" judgments.
In order to test the scientificity and accuracy of the method, the researchers conducted two blind test tests, the correct rate was 91.9% and 93.8%, respectively. Compared to the same type of detection technology, the accuracy rate is relatively high.
“Some technologies have blind test rates that are sometimes high, but this is only for the detection of certain exotic features. The composition of waste oil is complicated, and sometimes even a manufacturer or vendor has a very different composition of the waste oil produced in each batch. The results are not very reliable, and there is no such problem with the use of nuclear magnetic spectroscopy to detect the quality of the oil molecules themselves," said He Yujian.
It takes time to promote the road
The nuclear magnetic spectrum detection method is expected to open a window for the development of a national unified inspection standard for waste oil. However, the technology still faces some difficulties in its promotion.
It is understood that the use of the technology to detect a sample, generally at least half an hour or so. At the same time, testing costs is also a problem.
Cai Bo introduced that the acquisition of a 600 megawatt NMR instrument requires several million yuan, and that the operation process is highly professional and ordinary people cannot complete it on their own. He believes that the professionalism of equipment and equipment operation is the main factor limiting the promotion of the technology to the private sector.
However, He Yujian said that the cost of nuclear magnetic testing would be greatly reduced if the large quantities of samples were processed at one time. "The cost may also be a few bucks, and the relative time spent on each sample is much shorter."
He Yujian told reporters that the current research team has made new progress in the civilian use of technology. “In time, faster, simpler, and cheaper methods for on-site inspection of cooking oil will be used and used by law enforcement officers and the general public.â€
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