As paint thinner, ink and adhesives become dry, they can emit volatile organic compounds (VOCs), which can negatively impact 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. Because the isomers are so similar, it’s difficult to keep track of them separately.

Now, scientists have created an electric nose (“e-nose”) utilizing metal-organic framework (MOF) sheets that can accurately discriminate xylene isomer combinations, as reported in ACS Sensors.

If excessive amounts of xylene, also known as xylol, are inhaled or absorbed via the skin, it can be dangerous. Because each isomer, o-xylene, m-xylene, and p-xylene, interact differently in humans and other mammals, it is critical to monitor the environment for each isomer rather than their total presence.

The three types 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.

So, Lars Heinke and coworkers sought to determine whether MOF films might be included in simple, quicker sensors to detect and analyze the presence of each isomer in the air individually.

The researchers fabricated six distinct porous MOF films known to adsorb xylene isomers and mounted them on gravimetric sensors in an array referred to as an “e-nose.”

Initial tests revealed that the MOF films were sensitive to o-xylene, m-xylene, and p-xylene in distinct ways. Then, they tested how well the e-nose could tell the difference between xylene isomers in mixtures at 10 ppm and 100 ppm, which is the exposure limit set by the U.S. National Institute for Occupational Safety and Health.

The team was able to estimate the composition of the mixtures with 86 percent accuracy for the 10-ppm combination and 96 percent accuracy for the 100-ppm mixture using sensor array data and a machine learning technique.

The MOF-based e-nose, according to the researchers, is a simple device for distinguishing between the three types of xylene in environmental monitoring and diagnostic health testing.

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