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Researchers Create “E-Nose” to Steadily Differentiate Xylene Isomer Combinations

When paint thinner, ink, and adhesives dry, volatile organic compounds (VOCs) are released, which can be harmful to one’s health. One of the most common VOCs is xylene, which comes in three distinct isomers with the same components but slightly different configurations. As the isomers are so similar, it is difficult to individually keep track of them.

Researchers Create “E-Nose” to Steadily Differentiate Xylene Isomer Combinations.
An “e-nose” MOF-based sensor accurately distinguishes o-xylene, m-xylene, and p-xylene from mixtures. Image Credit: Peng Qin

Scientists have created an electric nose (“e-nose”) with porous metal-organic framework (MOF) films that can consistently differentiate xylene isomer combinations. The study was published in the journal ACS Sensors.

If excessive amounts of xylene, also known as xylol, are inhaled or absorbed via the skin, it can be dangerous. As each isomer (o-xylene, m-xylene, and p-xylene) reacts differently in humans and other mammals, it is critical to keep an eye on the environment for each one, rather than just the total amount.

The three forms of xylene were previously identified via gas chromatography analysis. However, this process necessitates the use of huge, expensive apparatus, and the analyses are time-consuming. To detect and analyze the existence of each isomer independently in the air, Lars Heinke and colleagues wanted to test if MOF films could be included in simple, quicker sensors.

Six distinct porous MOF films known to capture xylene isomers were produced and attached to gravimetric sensors in an array termed an “e-nose” by scientists. Preliminary tests revealed that the MOF films were sensitive to o-xylene, m-xylene, and p-xylene in distinct ways.

The e-nose’s ability to detect xylene isomers within mixtures was next evaluated at concentrations of 10 ppm and 100 ppm, which is the exposure limit set by the US National Institute for Occupational Safety and Health.

The team was able to estimate the composition of the mixtures with 86% accuracy for the 10-ppm combination and 96% accuracy for the 100-ppm mixture using sensor array data and a deep learning technique. The MOF-based e-nose, according to scientists, is a basic device for distinguishing between the three forms of xylene in environmental monitoring and diagnostic health testing.

The Alexander von Humboldt Foundation, the China Scholarship Council (CSC), and the Deutsche Forschungsgemeinschaft provided funding.

Journal Reference:

Qin, P., et al. (2022) VOC Mixture Sensing with a MOF Film Sensor Array: Detection and Discrimination of Xylene Isomers and Their Ternary Blends. American Chemical Society.

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