Analysis of polycyclic aromatic hydrocarbons in petroleum waxes and white mineral oils with appraisal of merits of different methods of analysis

Abstract

We present a critical discussion, based on our own experimental work, of the merits of two different methods for determining and estimating polycyclic aromatic hydrocarbon (PAH) compounds in refined paraffin waxes and white mineral oils. The Food and Drug Administration (FDA) in the USA has developed a method involving extraction of PAH compounds from wax for quantitative estimation by ultraviolet spectrophotometry of the total PAH content. In W. Germany two methods have been developed: one based on fluorescence of molten wax, the other on paper chromatography applied to a nitromethane extract of PAH compounds. The method employing fluorescence of the molten wax, however, is of little value, because the activating rays, wavelength 254 mμ are absorbed by mono- and bicyclic aromatic components naturally present in the wax. This leads to quenching of the fluorescence, even for waxes passing the requirements of the W. German sulphuric acid test intended to detect fluorescence quenchers. In the other method, the paper-chromatographic behaviour of the PAH extract of the wax is compared with that of three known carcinogenic PAH compounds. We have found that the retention values of these reference carcinogens, added intentionally to the wax extract, are not reproducible and that the fluorescent band is displaced irregularly by other components extracted from the wax, so that a comparison with the reference chromatogram is hardly possible. In addition, quenching takes place, the extent of which is dependent upon the type of PAH and on the type of wax. From our investigations, which cover more PAH compounds than those mentioned explicitly by the W. German law, we conclude that the reliability of both W. German methods is insufficient. We prefer the FDA method, because it is very reproducible and always gives the total PAH content. Moreover, this method has been developed in conjunction with toxicological experiments on animals.