Which analysis methods are suitable for analysis of Polycyclic Aromatic Hydrocarbons?

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

Anthracene

Anthracene

Benzo-a-pyrene

Benzo-a-pyrene

Chrysene

Chrysene

Naftacene

Tetracene

Pyrene

Pyrene

Phenanthrene

Phenanthrene

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.

Spectroscopic Methods

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

Chromatographic Methods

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.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

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