Summary and conclusions

Udvikling af analysemetode til bestemmelse af peroxider, tilstede eller frigjort i tandblegeprodukter

Development of a catalase bioassay for hydrogen peroxid measurement

Tooth whitening products are sold as retail trade in Europe. Therefore there is a demand for tests that enables authorities to control these products for the content of hydrogen peroxide. Almost all products contain either free or bound hydrogen peroxide that is released during the bleaching procedure. Some products contain a mixture of more hydrogen peroxide releasers that complicates the use of traditional chemical analytical methods. The aim of this project was to develop and validate a new analytical approach that enables an easy and precise determination of whitening agents in tooth bleaching products.

Development of a catalase bioassay for hydrogen peroxid measurement

A catalase bioassay was developed that was used to measure the content of peroxide in tooth whitening products. Hydrogen peroxide either present in a free state or bound in different types of releasing compounds was degraded enzymatically to water and oxygen that was measured by an electrode. Catalase (5000 units in 40ul phosphate buffer), the active enzymatic component in the assay, was added to a reaction chamber (100 ml) containing N₂ purged (O₂ depleted) phosphate buffer (pH = 7.0; 22°C). The chamber was closed with a lid on which an oxygen electrode was mounted. After the sample was injected (through small injection ports) the development in oxygen concentration was followed on a computer and when stabilised at a constant level recorded for subsequent calculation of total hydrogen peroxide content in the whitening product being analysed. The amount of hydrogen peroxide must not result in more than 80% of oxygen saturation in the reaction chamber to avoid bias from appearance of gas-bubbles. Comparison of the results from using the catalase bioassay with chemical analytical methods based on e.g. potassium permanganate titration confirmed that the bioassay was a useful alternative for analysing the hydrogen peroxide content in tooth whitening products.

The new catalase bioassay protocol was tested on hydrogen peroxide as well as urea peroxide, calcium peroxide, sodium perborate and sodium percarbonate. These hydrogen peroxide releasing compounds are all used in tooth whitening products including also products available on the Danish market. Furthermore the assay was used to determine the content of hydrogen or urea peroxide in 6 different tooth whitening products. The assay had coefficient of variation less than 2% and thus demonstrated a good reproducibility also compared to the chemical analytical methods traditionally used for determination of hydrogen peroxide in various forms.