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It still takes time for "NMR" technology to promote the development of trench oil
In a recent breakthrough, 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 oil. This technique involves converting the oil into a nuclear magnetic resonance (NMR) sample, which reveals the original structure of the oil, making it possible to identify counterfeit or degraded oils. The study was published in the first issue of *China Science: Chemistry* in 2013.
The key to evaluating oil quality lies in its molecular composition. "When people hear about NMR, they often think of medical MRI scans," He Yujian explained. "But this technology is widely used in the chemical industry." In cooking oil, hydrogen atoms within the molecules undergo chemical shifts when exposed to 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 differs significantly between fresh and degraded oils. According to He Yujian, the nutritional value of edible oil depends largely on the type and degree of unsaturation of its fatty acids. If chemical bonds break during processing or use, the degree of 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 molecular structure was previously uncommon. Dr. Cai Botai, a doctoral student in the research group, noted that some methods rely on detecting high-temperature breakdown products or foreign substances using gas or liquid chromatography. However, these techniques require predefined characteristics of waste oil, which may not cover all variations. As a result, many complex or "fine" types of waste oil can be overlooked.
Through extensive NMR analysis of over 60 samples of both edible and waste oils, the team identified 12 key differences in the nuclear magnetic resonance spectra. These differences help distinguish between good and bad oil. "We use NMR to check if the oil's molecular structure is intact and meets the required saturation levels without impurities," He Yujian said. "If any of these conditions are not met, the oil is considered poor quality."
However, during testing, the 12 indicators sometimes conflict. For example, one might suggest the oil is good, while another indicates it could be waste oil. To resolve such contradictions, multivariate data analysis is employed to ensure more accurate and reliable judgments.
To validate the method, the team conducted two blind tests, achieving accuracy rates of 91.9% and 93.8%, which are relatively high compared to other detection technologies. He Yujian emphasized that while some methods may show high accuracy, they often focus on specific features, whereas waste oil compositions can vary greatly, even between batches from the same manufacturer. NMR, on the other hand, directly analyzes the molecular quality, avoiding such inconsistencies.
Despite its potential, the widespread adoption of this technology still faces challenges. Testing a single sample typically takes at least 30 minutes, and the cost of operating an NMR instrument can be high. A 600 MHz NMR machine, for instance, costs several million yuan, and the operation requires highly trained professionals. Cai Botai believes that the complexity of equipment and procedures limits its use in private sectors.
However, He Yujian remains optimistic. He pointed out that processing large volumes of samples at once could significantly reduce costs, potentially bringing the price down to just a few dollars per test. Moreover, the time required for each sample would also decrease substantially.
The research team is currently working on making the technology more accessible for civilian use. "In the future, faster, simpler, and more affordable on-site testing methods for cooking oil will be available for law enforcement and the general public," He Yujian said. This advancement could play a crucial role in improving food safety and regulatory standards.