Comparison of pressurized fluid extraction, Soxhlet extraction and sonication for the determination of polycyclic aromatic hydrocarbons in urban air and diesel exhaust particulate matter M. Ryno¨, a L. Rantanen, b E. Papaioannou, c A. G. Konstandopoulos, c T. Koskentalo d and K. Savela* e Received 8th November 2005, Accepted 21st February 2006 First published as an Advance Article on the web 9th March 2006 DOI: 10.1039/b515882f In order to characterize and compare the chemical composition of diesel particulate matter and ambient air samples collected on filters, different extraction procedures were tested and their extraction efficiencies and recoveries determined. This study is an evaluation of extraction methods using the standard 16 EPA PAHs with HPLC fluorescence analysis. Including LC analysis also GC and MS methods for the determination of PAHs can be used. Soxhlet extraction was compared with ultrasonic agitation and pressurized fluid extraction (PFE) using three solvents to extract PAHs from diesel exhaust and urban air particulates. The selected PAH compounds of soluble organic fractions were analyzed by HPLC with a multiple wavelength shift fluorescence detector. The EPA standard mixture of 16 PAH compounds was used as a standard to identify and quantify diesel exhaust-derived PAHs. The most effective extraction method of those tested was pressurized fluid extraction using dichloromethane as a solvent. Introduction Diesel engine exhaust is an urban air pollutant containing several carcinogenic compounds in either gas or particle phase. Polycyclic aromatic hydrocarbons (PAHs) containing 2–5 benzene rings have shown to be in the gas phase and more than 5 rings have tendency to adsorb to the particles. Includ- ing molecular weight of PAHs also the meteorological and physical transformation processes influence in distribution between volatile and particulate phase. PAHs adsorbed onto the exhaust particles induce genotoxic and chronic effects in humans. 1–3 Diesel engine exhaust is considered probably (Group 2A) and gasoline engine exhaust possibly (Group 2B) carcinogenic to humans. 4,5 Diesel and gasoline engines emit particles and PAH compounds due to incomplete com- bustion of the fuel. The particulate mass and PAH emissions from diesel engines are generally higher than those of gasoline engines with a catalytic converter. 6–8 In this study we investigated three solvent extraction pro- cedures with three separate solvents in order to evaluate the most effective method to analyze particulate PAH compounds in environmental air samples and in diesel exhaust samples generated either directly from a car 9 or from a bench engine. To characterize the chemical composition of the particulate matter, urban air and diesel exhaust were collected on the glass fibre and Teflon-coated glass fibre (PTFE) filters. The effi- ciency of extracting PAHs from the particulates was compared between Soxhlet extraction, ultrasonic agitation and pressur- ized fluid extraction (PFE). 10–14 It should be noted that instead of PFE, PLE (pressurized liquid extraction) or ASE (acceler- ated solvent extraction) are used as abbreviations of the same extraction method in the literature. PFE is the liquid extraction of analytes from a solid matrix using an elevated temperature and pressure to enhance mass transfer. The system applies pressure so that elevated tem- peratures can be used during extraction without boiling the solvent system. The PFE method has been shown to be comparable to Soxhlet extraction for the determination of PAHs in a variety of environmental matrices. 11,15 This method has also been validated according to an extraction technique by NIST (National Institute of Standards and Technology) for the certification of natural matrix reference materials. 16 The PFE apparatus consists of a stainless steel extraction cell which is kept in an electronically-controlled oven during the extraction. The extraction cell is first filled with organic solvent and then pressurized and heated up to the desired temperature. The sample is extracted for a certain time (static extraction step), after which the solvent is transferred to a collection vial. The sample and the connecting lines are then washed with fresh solvent and finally, using a suitable gas, the residual solvent is purged from the sample and the connecting lines to the collection vial. The performance of this apparatus for many different environmental samples is well described by Bjo¨rklund et al. 11 The enhanced performance of liquid sol- vents at an elevated temperature and pressure compared to sonication or Soxhlet extraction is due to the disruption of the surface equilibrium, solubility and mass transfer effects. The elevated temperature disrupts strong solute-matrix interac- tions, decreases the viscosity of the solvent allowing improved a Finnish Institute of Occupational Health, Helsinki, Finland b Neste Oil, Porvoo, Finland c Aerosol & Particle Technology Laboratory, CERTH/CPERI, PO Box 361, Thermi 57001 Thessaloniki, Greece d Helsinki Metropolitan Area Council (YTV), Helsinki, Finland e National Veterinary and Food Research Institute (EELA), PL 45 (Ha ¨meentie 57), 00581 Helsinki, Finland. E-mail: kirsti.savela@eela.fi; Fax: þ358-9-3931811; Tel: þ358-9-3931953 488 | J. Environ. Monit., 2006, 8, 488–493 This journal is  c The Royal Society of Chemistry 2006 PAPER www.rsc.org/jem | Journal of Environmental Monitoring