Standardization of Thermal Desorption GC/MS Analysis for Polycyclic Aromatic Hydrocarbons and Comparison of Recoveries for Two Different Sample Matrices

The analysis of PAHs in environmental samples involves sampling, extraction, concentration and final analysis using GCMS. Traditional extraction of PAHs from a solid matrix, where much of the PAH reside, is a tedious and time consuming process. Thermal desorption (TD) can replace the traditional sample preparation step in the analysis scheme with a more efficient and direct method, which also eliminates the organic solvents used in the traditional extraction procedures, with the added advantage of significantly reducing the sample preparation time. This paper examines the recovery of standard PAHs solutions spiked on glass wool for different desorption times using TD techniques. Recoveries for desorption times ranging from 1 min to 20 min were studied. The peak areas obtained for individual PAHs increased as desorption time increased from 1 min to 15 min, while there was a decrease in peak areas as desorption times increased to 20 min. Therefore, the optimum desorption time for the highest recovery of PAHs was found to be 15 min. Coefficients of variation were calculated using the optimized desorption time for the PAH mix spiked on the glass wool substrate. It was found that low molecular weight and high molecular weight PAHs have high coefficients of variation (naphthalene 49%, Fluorene 24.2%, Dibenz(ah)anthracene 14.8%, Benz (ghi)perylene 15.5%), while the intermediate PAHs had much lower coefficients of variation (ranging from 0.5 % 4.0%). The method response was tested for linearity by analyzing the glass wool spiked with five different concentrations of PAH mixtures, ranging from 0.01 to 20ng/μL. The second part of the research examined the PAH recoveries from glass wool compared to Tenax spiked with PAH mixtures. This was performed by spiking the wool and 10 mg of tenax with 20ng/μL of the PAH mixture. The recovery of low molecular weight PAHs (having fewer numbers of rings) was larger in the case of Tenax than for the glass wool, whereas for the high molecular weight PAHs (having more rings), the recovery of PAHs from glass wool was larger than from the Tenax matrix.