The hydroperoxide challenge: overcoming a lack of standards

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  • Published: Jun 1, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
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The peroxide class of chemicals

Every year, over 2 million tonnes of hydrogen peroxide are produced. This colourless liquid is used as a bleaching agent and disinfectant, and even as a rocket fuel in concentrated forms, and is the simplest peroxide. Peroxides are chemicals that contain two oxygen molecules joined by a single bond. When one of these oxygens is also joined to a hydrogen atom, the chemicals are called hydroperoxides.

Every year, over 2 million tonnes of hydrogen peroxide are produced. This colourless liquid is used as a bleaching agent and disinfectant, and even as a rocket fuel in concentrated forms, and is the simplest peroxide. Peroxides are chemicals that contain two oxygen molecules joined by a single bond. When one of these oxygens is also joined to a hydrogen atom, the chemicals are called hydroperoxides.

Hydroperoxides have a wide range of applications, notably in plastics and paints, but can also be formed unintentionally. When hydroperoxides form in a food they can fundamentally change its taste. In the flavour and fragrance industry, these chemicals are a major nuisance. They form following the oxidation of some fragrance ingredients, such as essential oils, and are thought to be responsible for allergic reactions in skin – a hypothesis backed up by recent clinical tests.

The standard dilemma

Quantification of hydroperoxides is therefore important for the industry and various methods have been developed to monitor hydroperoxides in samples, including gas chromatography and liquid chromatography. However, all methods suffer from one major problem: the lack of a reliable standard. Hydroperoxide reference compounds are few and far between and extremely unstable; so unstable, in fact, that they have to be stored at -80 °C.

Some scientists have quantified samples using gas chromatography with flame ionisation detection (GC-FID) and mass spectrometry, using calibration standards created in house. However, because standards are not commercially available, none of the chromatographic methods have been validated. Recognising the limitations of this, researchers from the world’s largest fragrance and flavour company (Firmenich) set out to solve the problem.

Their solution relies on response factors. When standards of known purity are not available, GC-FID can be used alongside relative response factors. Response factors describe the ratio between the concentration of an analyte and the response of the detector to the compound. The relative response factor (RRF) between two analytes can be used to calculate the concentration of one analyte, if you already know the concentration of the other.

Usually RRFs are predicted using effective carbon number, but these researchers found that RRFs can actually be calculated from the molecular formula. They tried this on hydroxylated compounds (after silylation to improve stability) and were able to quantify and measure their purity, and decided to apply this approach to hydroperoxides.

Action on skin sensitisation

Also after silylation, GC-FID and predicted RRFs could be used to evaluate the purity of eight different hydroperoxide standards. Calibration with these standards gave straight lines with good determination coefficients, but all gave a slight negative offset due to breakdown of the hydroperoxides.

However, above a concentration of 500 mg/kg (500 parts per million), all of the analytes showed a recovery above 80% and quantification could be performed using the predicted RRFs.

They finally tested the method in a fragrance oil spiked with two of the hydroperoxide standards. GC-FID led to consistently low recoveries, which suggests that part of the sample was unavailable at the time of analysis. This is because, the researchers suspect, the hydroperoxides reacted with the many aldehydes in the fragrance oil.

Although this caused deviations in the results, the ability of hydroperoxides to form adducts with aldehydes could be a useful method for preventing their accumulation in products. However, the main utility of this study is the procedure it describes, which provides an effective alternative to classical internal standardisation and overcomes the lack of commercially available standards. This simple approach could be used for quality control of fragrance oils, which are found in a huge range of products, from perfumes and shower gels to air fresheners and cleaning products.

Related Links

Flavour Fragr. J. , 2016. Leocata et al.. Quantification of hydroperoxides by gas chromatography-flame ionization detection and predicted response factors.

Wiki: Hydrogen peroxide

Hydroperoxides and peroxides

Wiki: Organic peroxide

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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