Polycyclic Aromatic Hydrocarbons (PAH’s) consists of fused aromatic rings without heteroatoms or substituent groups. These are environmental contaminants resulting from incomplete combustion of fossil fuels such as coal and oil used for heating, cooking and industrial processes. PAH’s are found in oil, coal and tar deposits and also in edible oils, roasted and smoked meat, groundwater and soils. Human exposure by ingestion is a major concern as these can be highly carcinogenic.
Examples of PAH’s
Analytical Procedures for Estimation of PAH’s
Polycyclic aromatic hydrocarbons are nonpolar and have low volatilities. As they are less soluble in water they are found mainly in soils, sediments, oils or in air- bone suspended particulates. Analysis techniques commonly adopted for their identification and estimation are spectroscopy, chromatography and mass spectrometry.
PAH’s show characteristic UV absorbance spectra. Absorption bands are specific for each ring structure and it is possible to identify different isomers. Most PAH’s also have high fluorescence sensitivity which is useful for low-level determinations
Gas chromatography with flame ionization detection provides a sensitive method for estimation of PAH’s but there can be interferences due to presence of carbonaceous impurities. Trace and ultra trace analysis is routinely carried out using electron ionization detector.
Liquid chromatography is the preferred method because of the low volatalities of PAH’s. UV and fluorescence detection systems provide low level detections. Samples of PAH’s are stored in glass containers, protected from light and stored under refrigeration. Extractions are usually done in dichloromethane and then exchanged into acetonitrile prior to gradient HPLC analysis using different water/acetonitrile gradients. UHPLC analysis shortens analysis time and provides a high throughput when large number of samples are to be analysed.
Mass Spectrometry Techniques
GC- MS and LC- MS are preferred techniques for low level qualitative and quantitative estimation of PHA’s. GC- MS is commonly used but involves time-consuming separations. Triple stage mass spectroscopic separations, ie, GC-MS-MS and LC-MS-MS permit highest levels of separation efficiencies for ultra-trace level estimations.