The rapid measurement of polycyclic hydrocarbons in air by microsublimation
Interest in the carcinogenic factors associated with combustion processes goes back to about 1800, when skin cancer was observed as an occupational disease of chimney sweeps. Benzo(a)pyrene (BaP), a carcinogenic polycyclic hydrocarbon, was only isolated from coal tar Ca. 1950 by Kennaway by means of its fluorescence properties and BaP has been observed by various workers as a frequent constituent of air samples and biological materials. Up until quite recently, the methods used by most workers were based on ultraviolet absorption; fluorescence had been forgotten. These methods have been laborious in execution and unreliable. When, in the ultraviolet, diagnosis and measurement of BaP was based on the peak at Ca. 402 mn, results had to be particularly unreliable because of the strong interference of benzo(k)fluoranthene (BkF) which was always present in the same extracts or eluants. The interfering effect of BkF was pointed out in 1960 but ultraviolet measurements of BaP continue to be made without correction for BkF. In our laboratory, over a period of 15 years, continuing improvements and new techniques have led to the use of activated alumina for chromatographic separation using toluene, a polar solvent, for elution, followed by fluorescence measurement of BaP and BkF. Using this more rapid method, it has been found possible to make daily measurements of these 2 polycyclic hydrocarbons in Ottawa air over a period of several years. This fairly rapid method does retain the lengthy soxhiet extraction of each sample, followed by a shortened chromatographic separation. In the method to be described, both the extraction and chromatography are dispensed with by direct sublimation of the polycyclics from the air sample. The sublimation is carried out at an optimum temperature under an inert atmosphere, the sublimate is collected in spectrograde solvent and the BaP and BkF are measured by fluorescence in the usual way. The results obtained by sublimation agree very well with those carried out by our present standard method. Being simpler and more rapid, it should be quite feasible to make this the basis of a rapid method for the routine measurement of BaP and BkF levels as indicators of air pollution, analysing 20 or more air samples per day.