5 Assessment of results and conclusion

Development of an analysis method to determine peroxides in or released from tooth-whitening/dental-bleaching products.

A new method and protocol for the analysis of peroxide content in tooth-whitening products was developed. The method is based on the measurement of changes in oxygen concentrations following enzymatic conversion of peroxide to oxygen and water. Compared to traditional analytical methods, based on titrations with permanganate and thiosulfate, the newly developed catalase bioassay is easy to conduct, and all peroxide compounds – irrespective of whether they are bound to different releasers – may be measured at once. The peroxide contents found in the tooth-whitening products correspond well with the product specifications.

Results of method development and product analysis can be summarised as follows:

Determination of peroxide content in tooth-whitening products through use of catalase bioassay is quick and easy.
The catalase bioassay is robust, simple, quick, highly sensitive and has good reproducibility (coefficient of variation < 2%).
The bioassay can determine the content of peroxides with great accuracy in products with very low concentrations of active substance. The lower detection limit is 0.0002% hydrogen peroxide in the product.
In contrast to traditional redox titrations, the bioassay is not affected by any reducing or oxidising chemicals in the products.
The catalase bioassay is suitable for tooth-whitening products with hydrogen peroxide as the active substance, no matter whether the peroxide is present as free hydrogen peroxide or bound in releasers.
Products containing several different active substances may be tested, e.g. products containing both urea peroxide and calcium peroxide (1).
It is highly probable that the bioassay may be suitable for use on other product types containing hydrogen peroxide, e.g. cosmetics containing fat, which complicates redox titrations.
For four of the products tested, the concentrations found using the catalase bioassay and potassium permanganate titration corresponded well with the product specifications.
For three of the products tested, the concentration of active substances was not stated.
In repeated analyses of the same batch, two of the products tested (”E” and ”F”, which come in a set) showed no – or a very small – content of peroxide, both using the titration method and the catalase bioassay method. Both analysis methods found peroxide when a new set was bought and tested.