ORIGINAL PAPER Optimisation of the extraction of polycyclic aromatic hydrocarbons and their nitrated derivatives from diesel particulate matter using microwave-assisted extraction F. Portet-Koltalo & K. Oukebdane & F. Dionnet & P. L. Desbène Received: 12 July 2007 / Revised: 20 September 2007 / Accepted: 8 October 2007 / Published online: 6 November 2007 # Springer-Verlag 2007 Abstract Pressurised microwave-assisted extraction was used to extract a complex mixture containing polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs and heavy n- alkanes from a particularly refractory carbonaceous material resulting from the combustion in a diesel engine. A second- order central composite design was used to determine the optimal conditions of extraction in terms of time, temper- ature, volume and nature of extracting solvent from spiked diesel soots. To begin, methylene chloride, tetrahydrofuran and chloroform were tested for extracting the spiked diesel particulates; however, the nature of these solvents was not really an influential factor. Volume was the most influential factor and was kept at a medium level to enhance the extraction of heavy PAHs without introducing an important dilution factor. Temperature and time were not influential as main factors but interacted with the other factors. Finally, high temperature and duration associated with a medium volume of methylene chloride were better for the extrac- tions. After this optimisation, five-ring and six-ring PAHs were nevertheless not satisfactorily desorbed. Other sol- vents were therefore tested. Only aromatic ones, and particularly heterocyclic aromatic solvents, managed to desorb the heaviest PAHs. Pyridine, with its both aromatic and its basic character, was the most successful solvent. Desorption was even complete with an addition of 17% of diethylamine into pyridine. So, using MAE, we succeeded in extracting quantitatively, from the spiked refractory diesel soot surface, two-ring to six-ring PAHs, heavy n- alkanes and short nitrated PAHs. However, heavy nitrated PAHs were better extracted with a small addition of acetic acid (1%) into pyridine instead of a basic cosolvent. Keywords Polycyclic aromatic hydrocarbons . Diesel particulate matter . Microwave-assisted extraction . Factorial design Introduction Diesel particulates which consist of soot spheres occur during combustion processes [1]. They can adsorb complex mixtures usually containing thousands of organic compo- nents, such as polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (nitroPAHs) and aliphatic hydrocarbons. Fuel PAHs may survive intact the combustion process of diesel engines, with the same carbon skeleton, but can also recombine with other fuel fragments to produce other PAHs and even nitroPAHs, by reaction of PAHs with oxides of nitrogen [2, 3]. In fact, PAHs are mutagenic after metabolic activation, whereas nitroPAHs are powerful direct-acting mutagens. For example, 1-nitropyrene is one of the most active mutagenic compound as well as 6- nitrochrysene or some dinitroPAHs [4]. They can have higher carcinogen potentials than benzo[ a]pyrene or dibenzo[a,l]pyrene, which have the highest toxic equivalent factors among all the native PAHs [5]. Consequently it is obviously of major interest to analyse PAHs and their nitrated derivatives. Analytical schemes used to identify Anal Bioanal Chem (2008) 390:389–398 DOI 10.1007/s00216-007-1684-2 F. Portet-Koltalo : K. Oukebdane : P. L. Desbène (*) Laboratoire d’Analyse des Systèmes Organiques Complexes, UPRES 3233-IRCOF et IFRMP, Université de Rouen, 55 rue Saint Germain, 27000 Evreux, France e-mail: paul-louis.desbene@univ-rouen.fr F. Dionnet CERTAM, Technopole du Madrillet, 1 rue Joseph Fourier, 76800 Saint Etienne du Rouvray, France