The use of electron spin resonance spectrometry with a modern instrument is described for the determination of polynuclear aromatic hydrocarbons (PAHs) down to nanogram levels, after adsorption on calcined silica/alumina. A single PAH or the total number of moles of PAHs can be determined. Implications for liquid chromatography are discussed.
Polycyclic aromatic hydrocarbons (PAHs) are probably the most widespread of all chemical environmental pollutants with the potential for carcinogenicity and mutagenicity in humans. Because these compounds are produced in virtually all combustion processes and in degradation processes of organic materials, they are often present in environmental samples as extremely complex mixtures and in almost every type of sample matrix. The identification and determination of PAHs are therefore of fundamental importance to those engaged in environmental assessment. Modern analytical methods for PAHs have been reviewed in detail recently [l-3],
but no reference was made to the use of electron spin resonance (e.s.r.) spectrometry in this area.
The application of e.s.r. for the detection and estimation of a number of hydrocarbons (anthracene, 9,10-dimethylanthracene, perylene, naphthacene) was reported [4] as early as 1962. These compounds are quantitatively converted to the cation-radical form on the surface of a strongly calcined silica/ alumina adsorbent of the type normally used as a catalyst in the cracking of hydrocarbons. The resulting radical species are stable in the adsorbed state. The PAR concentration in an unknown solution can, therefore, be determined by direct comparison of the signal for the unknown with that obtained from a standard solution of the same compound. Unfortunately, because of the overlap of spectra from individual PAHs, the e.s.r. method is not specific. Hitherto, therefore, the technique was not generally applicable to mixtures of these compounds, nor was it widely adopted. Recent advances in separation techniques, particularly capillary column gas chromatography [5] and high-performance liquid chromatography (h.p.1.c.) [6] have transformed the situation.