Exposing the toxic whitening agents in food packaging

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  • Published: Apr 14, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: HPLC
thumbnail image: Exposing the toxic whitening agents in food packaging

Whiter and brighter

By offering solutions to commercial problems, chemistry can make products more desirable. For example, after clothes come out of the wash, they sometimes have a yellowish tint – not quite what consumers are looking for in their fresh laundry. So, as well as bleach and water softeners, laundry detergents generally contain brighteners to make clothes appear whiter and cleaner. In hair conditioner, brighteners are also sometimes added to enhance the glow of blonde hair.

By offering solutions to commercial problems, chemistry can make products more desirable. For example, after clothes come out of the wash, they sometimes have a yellowish tint – not quite what consumers are looking for in their fresh laundry. So, as well as bleach and water softeners, laundry detergents generally contain brighteners to make clothes appear whiter and cleaner. In hair conditioner, brighteners are also sometimes added to enhance the glow of blonde hair.

These brightening agents work by absorbing invisible UV radiation, re-emitting it as light in the visible range by fluorescence and increasing the brightness of the material. These chemicals are known as ‘fluorescent whitening agents’ or FWAs, and are also used in textiles, plastics and paper.

The most common whitening agents used in the paper industry are based on 4,4′-diaminostilbene-2,2′-disulfonic acid (DSD), which is associated with health and safety issues. If they enter the body, DSD-based whitening agents can be absorbed by the gut, after which they may enter the blood stream and rapidly spread throughout the body. Some such chemicals have toxic effects and may even contribute to cancer, leading China, the EU and many other countries to limit their use in food packaging. In some cases, they are banned altogether.

In order to enforce legislation, authorities need a method to not only detect these agents but also quantify them, and in a wide range of sample types. However, currently there is no standard method for analysing FWAs in paper used for food packaging (known in the industry as food contact paper).

The search for a suitable method

Methods trialled previously include UV irradiation and fluorospectrophotometry – neither of which can identify the type of whitening agent present, and HPLC-MS – which is expensive and requires a highly trained operator. HPLC, however, does have potential for detecting FWAs as it offers high sensitivity fluorescence detection. To capitalise on the potential of this method, researchers from Xiangnan University in China devised an alternative way of using it. “We propose a method for the separation of fluorescent whitening agents by using an ionic liquid as the additive of the mobile phase,” explains Dr Qing Wang.

Ionic liquids – a novel class of solvents – have become popular for a wide range of applications, thanks to their stability, wide liquid range, solubility and recyclability. They have been used to separate a wide range of compounds by HPLC, including proteins, antibiotics and a long list of pharmaceuticals. However, until now, ionic liquids had not been used to analyse FWAs.

The key to compliance

The researchers used HPLC with fluorescence detection to separate 11 different whitening agents. They evaluated the effects of several parameters on separation, finding that TBABF4 (tetrabutylammonium tetrafluoroborate) was the optimal ionic liquid for separation, and at a concentration of 8 mM.

The optimised procedure was applied to four food contact paper samples purchased from a local market. The researchers were unable to detect any of the target FWAs in the samples, which suggests that manufacturers are complying with regulations.

As the researchers could not identify FWAs in the market samples, they spiked paper samples with the chemicals. Good recoveries were obtained for all of the whitening agents, proving the method’s applicability to real samples.

This is the first reported use of an ionic liquid to separate whitening agents by HPLC. It represents a straightforward method for analysing these potentially toxic chemicals, and may help to enforce regulation. “The method is simple, accurate, and can be used for supervising the abuse of FWAs in food-contact paper effectively,” says Wang, who is currently working on an even more sensitive method, able to detect just trace amounts of FWAs.

Related Links

J. Sep. Science. 2016., Wang et al.. Ionic liquid as a mobile phase additive in high-performance liquid chromatography for the simultaneous determination of eleven fluorescent whitening agents in paper materials.

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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