Plastic packaging pongs profiled by 2D GC

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  • Published: Jun 15, 2017
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
thumbnail image: Plastic packaging pongs profiled by 2D GC

Unpleasant odours limit the uses of recycled plastic

There are strong environmental benefits to recycling plastic, and in many countries large amounts of plastic packaging are collected for this purpose. Recycled plastic packaging may have been used to store food, drinks, cosmetics or cleaning products, many of which will leave some odour behind. The possibility of odour tainting food has meant that there has been little use of recycled plastic in the food industry, with typical uses being in other areas, such as beverage crates and flower pots.

Few comprehensive studies have been carried out to date on the odour profiles of waste plastic. The researchers from Erlangen and Freising used 2D GC-MS to examine the odorous compounds from waste consumer packaging plastic put out for recycling. A panel of 10 trained volunteers was used to smell the GC effluent and identify odorous compounds.

Odorous compounds detected in waste plastic by 2D GC

Pieces of plastic were washed with water and then extracted with dichloromethane. The volatiles were separated from non-volatile compounds by solvent-assisted flavour evaporation (SAFE). The volatiles were concentrated by distillation through a Vigreux column prior to GC studies.

Initially, 1D high-resolution GC runs were carried out on two different GC columns. The first GC used a Thermo Fisher TRACE GC Ultra instrument with a J & W Scientific DB-FFAP column and a 40 to 230 °C gradient. The GC effluent was split into two streams, one going to a flame ionisation detector (FID) and one to a sniffing port for odour analysis. The second 1D GC also used the same instrument, this time with a J & W Scientific DB-5 column and a 40 to 250 °C gradient. A split between an FID and a sniffing port was again used.

2D GC runs were carried out with two Agilent CP3800 GCs. The mixture was first separated on a J & W Scientific DB-FFAP column, with a temperature gradient of 40 to 230 °C. After the first column, the effluent was split into two streams, one going to an FID and one to a sniffing port. A Gerstel CTS 1 Cryo Trap System at -100 °C was used to trap effluent from the first column, which was then put onto the second column, a J & W Scientific DB-5 run with a gradient from 40 to 250 °C. The effluent from the second column was split between a mass spectrometer (Agilent Saturn 2200) and a sniffing port.

The initial material gave a mixture of ‘spicy’, ‘dusty’, ‘fatty’ and ‘woody’ odours, with the former being the strongest. The GC experiments identified 33 odorous compounds based on their odour and retention time, 21 of which were confirmed by mass spectrometry. Some of these compounds could be clearly seen on the 1D GC, while others needed the 2D GC to give acceptable separation.

A number of unsaturated aldehydes were present, giving rise to ‘fatty’ odours. These were presumably derived from fatty acids from foodstuffs, or from fatty acid derivatives used as lubricants. Compounds with a musty or mouldy odour, such as 2-methylisoborneol and patchouli alcohol, were also detected. Raspberry ketone, used as a food flavouring and a perfume ingredient, gave a distinct raspberry odour. The lactone sotolone, which is found in a number of foodstuffs, may be largely responsible for the ‘spicy’ odour noted in the waste material.

1D and 2D GC give overall picture of waste plastic odour

The combination of 1D and 2D GC allowed an overall picture of the odour compounds in waste plastic to be produced, which is a crucial first step towards dealing with the problem. Such an approach could be used in other waste streams where odours limit recycling, and could allow a truly ‘circular’ economy to develop.

Related Links

J. Sep. Sci., 2017, 40, 1500-1507. Strangl et al. Characterization of odorous contaminants in post-consumer plastic packaging waste using multidimensional gas chromatographic separation coupled with olfactometric resolution.

J. Sep. Sci., 2009, 32, 883-904. Cortes et al. Comprehensive two dimensional gas chromatography review.

Eur. Food Res. Tech., 1999, 209, 237-241. Engel et al. Solvent assisted flavour evaporation – a new and versatile technique for the careful and direct isolation of aroma compounds from complex food matrices.

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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