Now a team led by Professor Hongbin Ding at the Dalian University of Technology, in northeastern China, has developed a new method, using laser-induced breakdown spectroscopy (LIBS), to differentiate safe cooking oil from toxic gutter oil.

Prof. Ding and colleagues at the university's School of Physics and Optoelectronic Engineering, describe how they developed and tested the new technique in the Chinese Science Bulletin.

Gutter oil - which the Chinese call "di-gou-you" - is leftover oil from restaurants, and is widely used in China. In their paper, the authors describe how investigations show gutter oil - which they refer to as trench oil - contains toxic substances ranging from harmful bacteria to heavy metals and fatty acids.

In the long term, consumption of gutter oil can lead to serious liver problems, including cancer, and it can cause developmental disabilities in children and newborn babies.

Trade in gutter oil persists as authorities lack effective detection tools

However, despite punitive measures by the Chinese government, the lucrative trade in gutter oil persists. The situation is further hampered by a lack of tools that rapidly distinguish illegal gutter oil from legitimate edible cooking oil.

Illegal traders use various techniques to make gutter oil look like genuine edible cooking oil: they bleach it to make it lighter in color, and they add alkalis to neutralize the acidity caused by the high levels of animal fats.

Based on stories in the Chinese press, if you eat out in China, you are likely to be unwittingly consuming gutter oil at a rate of one in every ten restaurant visits.

In their study, Prof. Ding and his team show how a technique called laser-induced breakdown spectroscopy (LIBS), which is used in the quantitative and qualitative analysis of solids, liquids and gases, can be used to rapidly differentiate between gutter oil and legitimate edible cooking oil.

LIBS is one of the technologies that the ChemCam on NASA's Curiosity rover is using to analyze rocks.

First study to show successful use of LIBS to detect gutter oil

In this study, the device uses a high-energy laser beam to vaporize and excite a sample of the oil into a plasma that emits a unique spectrum characteristic of the chemical composition of the oil.

By analyzing the spectrum using principal component analysis (PCA) combined with an Artificial Neural Network (ANN) model, the team created a new approach that uniquely identifies the elements in the gutter oil, and allows it to be quickly and efficiently differentiated from genuine cooking oil.

The LIBS technique is viewed a big step forward in chemical analysis because it has many advantages over current methods such as requiring little or no sample preparation, its fast analysis time, and the fact it can sense substances remotely - on Mars some of the rocks LIBS is sampling are up to seven meters away from the rover.

The study is the first to report successful use of LIBS to detect gutter oil. Prof. Ding and colleagues have developed software that allows rapid analysis from a single shot LIBS spectrum. They conclude:

"The achieved identification accuracy based on PCA and ANN was 94.2%, 98.1%, respectively. This indicates that LIBS detecting technique based on PCA and ANN statistical analysis brings a new possible approach to identify trench oil efficiently and quickly."

REFERENCE:

Preliminary study of identifying trench oil based on laser-induced breakdown spectroscopy, Wu Ding et al, Chinese Science Bulletin, DOI: 10.1360/N972013-00042, Abstract.