AIR SAMPLING AND ANALYSIS OF POLYCYCLIC AROMATIC-HYDROCARBONS

Polycyclic aromatic hydrocarbons (PAHs) occur in particles or in vapour phase. The size of the particles is affected by the season: in the winter there is a shift from large to small particles. PAHs, which are associated with particulate matter, are usually collected on filters and are then vaporized from the filter, or exist in the vapour phase and are trapped by a back-up solid sorbent. Many PAHs can react with other environmental pollutants. Benzo[a]pyrene deposited on a filter was reported to undergo chemical reactions with ozone and nitric acid. The loss of benzo[a]pyrene can be as high as 85%. The most common sampling method applied is integration of the sample by pumping the air stream through a sample device (active sampling). Passive sampling relies on the diffusion-controlled gradients towards a surface. Passive sampling is more often used for vapour-phase PAHs in occupational environments. Sample clean-up is increasingly performed by solid-phase extraction and is also applied to air samples. The samples are traditionally desorbed using Soxhlet apparatus, ultrasonication and various organic solvents, but supercritical fluid extraction is getting more popular. The analysis of PAH samples is usually carried out by high-performance liquid chromatography equipped with a fluorescence detector or gas chromatography-mass spectrometry with electron and negative chemical ionization methods. For quantitative analysis the correlation of these two methods have shown to be good. In qualitative analysis mass spectrometry lacks the ability to resolve the isomeric structures and high-performance liquid chromatography with time programming fluorescence seems to be the detection method of choice.