Many volatile organic compounds (VOCs) are hazardous to human health, with several classified as carcinogenic i.e. capable of causing cancer in humans. One particular group of VOCs, referred to as aromatic hydrocarbons or simply ‘aromatics’ because of their sweet, pleasant smell are of particular interest because of their widespread use.

Detecting Benzene

Benzene (C₆H₆) is a clear, colourless and highly flammable liquid with a sweet petrol-like smell. Most people can just detect its distinctive smell at concentrations between 2.5 and 5 parts per million (ppm) in air. Benzene occurs naturally in crude oil and is also found in ambient air as a result of burning fuels, such as coal, petrol and wood and is common in unleaded fuel, where it is added as a substitute for lead, allowing smoother running.

Detecting Toluene

Toluene (C₇H₆), also known as methylbenzene, is a colourless liquid, with a strong, solvent-like smell. Widely used as an industrial feedstock as well as a solvent, toluene is a highly flammable chemical. Toluene is found naturally at low levels in crude oil and is a by-product of the production of petrol (gasoline) as well as the production of coke from coal. Purification is done during a final separation by any distillation or solvent extraction process used for BTEX aromatics.

Detecting Ethylbenzene

Ethylbenzene (C₈H₁₀), is a colourless liquid, with a petrol-like aroma. Ethylbenzene is widely used in industrial processes for the manufacture of styrene, one of the most common plastics, which is then used for polystyrene manufacture. Although 99% of ethylbenzene is used in the production of plastics there are other uses for the monocyclic aromatic hydrocarbon, including fuel, solvent in ink, rubber adhesive, varnish and paints.

Detecting Xylene

Xylene (C₈H₁₀) is the term used to describe the three isomers of dimethyl benzene; m-xylene, p-xylene and o-xylene. Usually concentrations of each are added together as total xylenes. Xylene is refined from crude oil, and is a clear, greasy liquid.