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It still takes time for "NMR" technology to promote the development of trench oil
In recent years, a research team led by Professor He Yujian from the College of Chemistry and Chemical Engineering at the University of Chinese Academy of Sciences, along with researcher Zhongwei Ke from the China Institute of Inspection and Quarantine, has developed an innovative method for detecting waste cooking oil. The technique involves first subjecting the oil to nuclear magnetic resonance (NMR) analysis, which can reveal the original structure of the oil, even if it has been altered or contaminated. This groundbreaking research was published in the first issue of *China Science: Chemistry* in 2013.
To assess the quality of oil, scientists now rely on its molecular characteristics. "When people hear about NMR, they often think of medical imaging, but this technology is widely used in the chemical industry," explained He Yujian. In cooking oils, hydrogen atoms within the molecules experience chemical shifts under strong magnetic fields. These shifts vary depending on the molecular environment, allowing researchers to determine the composition of edible oils based on their NMR spectra.
Edible oils are primarily composed of triglycerides—molecules made up of glycerol and three fatty acids linked by ester bonds. The state of these fatty acids determines the differences between edible oil and waste oil. According to He Yujian, the nutritional value of oil lies in the type and degree of unsaturation of its fatty acids. If chemical bonds break during processing or use, the unsaturation decreases, leading to the formation of polymers, which signals a decline in oil quality.
This new approach to identifying waste oil by analyzing the internal structure of fat molecules is not commonly used before. Dr. Cai Botai, a doctoral student in the research group, noted that some methods, such as gas chromatography and liquid chromatography, detect waste oil by looking for high-temperature byproducts or foreign substances. However, these techniques often require predefined characteristics of waste oil, which can lead to missed cases or false positives.
The team conducted NMR tests on over 60 samples of both edible and waste oils, creating a comprehensive spectral map. By comparing the data, they identified 12 key differences that could help distinguish good oil from bad. "With NMR, we can check whether the oil’s molecular structure is intact, its saturation level meets standards, and there are no impurities," said He Yujian.
However, the 12 indicators sometimes conflict. For example, one might suggest the oil is good, while another indicates it may be waste. To address this, the team uses multivariate data analysis to make more accurate and reliable judgments. In two blind tests, the method achieved correct identification rates of 91.9% and 93.8%, significantly higher than other similar technologies.
He Yujian emphasized that while some techniques may have high accuracy for specific types of waste oil, the complexity of real-world samples makes them less reliable. In contrast, NMR focuses on the molecular structure itself, offering a more consistent and trustworthy evaluation.
Despite its potential, the technology still faces challenges in widespread adoption. Testing a single sample typically takes at least 30 minutes, and the equipment costs are high. A 600 MHz NMR instrument can cost several million yuan, and the operation requires specialized knowledge. Cai Bo believes that the high level of expertise needed limits the technology's use in the private sector.
However, He Yujian remains optimistic. He pointed out that when large numbers of samples are processed together, the cost per test could drop significantly, making the method more affordable. "Eventually, faster, simpler, and cheaper on-site testing methods for cooking oil will become available for law enforcement and the public," he said.
The team is already working on improving the practicality of the technology for civilian use, aiming to make it accessible and efficient for everyday applications. With continued development, this NMR-based approach could play a crucial role in ensuring the safety and quality of cooking oils nationwide.