Sonolytic reactions of phenanthrene in organic extraction solutions

Ultrasonic extraction is a common method used to extract semi-volatile and nonvolatile organic compounds such as polycyclic aromatic hydrocarbons (PAHs) from solid matrices. However, ultrasonic energy has been suspected to lead to undesired reactions of the solute and thus affect qualitative and quantitative results. In this paper, sonolytic reactions of phenanthrene in common organic extraction solutions were examined using a 20 kHz ultrasonic probe under conditions commonly used for ultrasonic extraction. Extraction parameters including phenanthrene concentration, solvent type, pulse length, and sonication time were investigated. Hexane:acetone (1:1 V/V) resulted in less phenanthrene degradation than dichloromethane (DCM):acetone (1:1 V/V). Initial solute concentration, length of sonication time, and solvent type affected the degradation of phenanthrene. Reaction byproducts including methylphenanthrene and methylnaphthalene detected after sonication indicate that phenanthrene reacts by both direct pyrolysis and reaction with methyl or ethyl radicals formed from solvent pyrolysis.