Gasoline, Kerosene, and Diesel Fingerprinting via Polar Markers Renato Haddad, †,§ Thaís Regiani, † Cle ́ cio F. Klitzke, † Gustavo B. Sanvido, † Yuri E. Corilo, † Daniella V. Augusti, ‡ Va ̂ nya M. D. Pasa, ‡ Rita C. C. Pereira, ‡ Wanderson Roma ̃ o, † Boniek G. Vaz, † Rodinei Augusti, ‡ and Marcos N. Eberlin* ,† † ThoMSon Mass Spectrometry Laboratory, Institute of Chemistry, University of Campinas (UNICAMP), 13083-970 Campinas, Sã o Paulo (SP), Brazil ‡ Department of Chemistry, Federal University of Minas Gerais (UFMG), 31270-901 Belo Horizonte, Minas Gerais (MG), Brazil ABSTRACT: Venturi easy ambient sonic-spray ionization mass spectrometry working in the liquid mode (V L -EASI-MS) is shown to provide rapid and reliable characterization of crude oil distillates. With no extraction or pretreatments, samples of gasoline, kerosene, diesel, and admixtures of gasoline/diesel and gasoline/kerosene were directly analyzed by V L -EASI(+)-MS. Homologous series of natural N-heteroaromatics were detected in their protonated forms providing typical profiles of polar markers. For gasoline, V L -EASI(+)-MS detects a homologous series of mainly C1-C5 alkyl pyridines. For kerosene, a typical series of alkylated tetrahydroquinolines is detected. For diesel, the V-EASI(+)-MS profile is much richer because of the detection of several classes of many N-heteroaromatics. V L -EASI(+)-MS is also shown to provide typical spectra for petrochemical gasolines detecting specific antioxidants. Admixtures of gasoline/kerosene and gasoline/diesel are also clearly characterized with limits of detection of 10 and 1% (v/v), respectively. Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) has been used to confirm assignments of the polar markers detected by V L -EASI(+)-MS. ■ INTRODUCTION Gasoline, kerosene, and diesel are mainly composed of complex mixtures of homologous series of hydrocarbons (HCs) obtained from petroleum refining. 1 Gasoline is a light crude oil product containing a HC distribution from C4 and C12 carbon atoms. Kerosene contains HCs from C8 to C18 carbon atoms, whereas diesel is much heavier and is comprised of HCs with C8-C40 carbon atoms. The characterization and quality control of such complex HC mixtures are therefore normally performed via gas chromatography separation, 2 which provides typical profiles of the increasingly heavier and diverse HC homologous series of gasoline, kerosene, and diesel. Crude oils are also characterized by gas chromatography via HC profiles. However, alternatively, this highly complex mixture can also be comprehensively characterized by direct mass spectrometry (MS) analysis without pre-separation steps via profiles of their polar components. These natural components have been shown to function as natural markers for major crude oil properties, such as type, origin, and biodegradation, in a field that has became known as petroleomic MS. 3 Recently, ambient mass spectrometric techniques requiring no pre-separation or sample preparation protocols have been introduced, 4 and the application of this technique to fuel analysis has been demonstrated. 5 We have shown that comprehensive analysis of crude oils 6 can be performed via direct desorption and ionization performed at ambient conditions using one of such techniques: easy ambient sonic-spray ionization (EASI). 7 EASI-MS has also been widely and successfully used to the direct analysis of biodiesel. 8 More recently, we have introduced a simpler variant of EASI, named Venturi EASI (V-EASI) 9 able to operate in dual mode for liquid (V L -EASI) or solid (V S -EASI) samples. The technique simplifies analysis by eliminating electrical pumping and incorporating solution self-pumping because of the Venturi effect. In the V L -EASI mode, it uses a high stream of nitrogen or gas to produce both self-pumping of the analyte solution and proper ionization via sonic spray 10 (Figure 1). Additionally, adulteration of fuel is a common illegal practice worldwide, and gasoline has been adulterated by the addition of kerosene or diesel. 11 Herein, we test the use of V L -EASI as a direct method of characterization and quality control of three major crude oil distillates: gasoline, kerosene, and diesel. ■ EXPERIMENTAL SECTION Reagents and Samples. Samples of gasoline (C type) and diesel (one of each raw material) were supplied by the Analytical Center at the University of Campinas. A commercial sample of kerosene was purchased at King, Ltd. (Rio de Janeiro, Brazil). All of the samples were within the specifications of the Brazilian Agency for petroleum and fuels (ANP regulation 309/2001). Gasoline was adulterated by the addition of diesel at the following proportions (%, v/v): 99:1, 90:10, 75:25, and 50:50. Blends of gasoline and kerosene were prepared at the 90:10, 75:25, and 50:50 (%, v/v) proportions. The samples of gasoline, diesel, kerosene, and admixtures (500 μL each) were dissolved in 1 mL of methanol [with 0.1% (m/v) of formic acid], and the resulting solutions were transferred to Eppendorf tubes to be analyzed by the V-EASI-MS device (Figure 1). V L -EASI-MS. The V-EASI source used was constructed as described in details elsewhere. 9 Briefly, in one of the holes of the T-shaped pipe (stainless steel), a silica capillary with a diameter of 100-125 μm was connected. By the Venturi effect, the solutions in the Eppendorf tubes were self-pumped at a flow rate of roughly 20 μL min -1 and sprayed directly into the entrance of the mass spectrometer (a single quadrupole instrument, model 2010EV, Shimadzu Corp., Japan) Received: February 17, 2012 Revised: April 23, 2012 Published: April 30, 2012 Article pubs.acs.org/EF © 2012 American Chemical Society 3542 dx.doi.org/10.1021/ef300277c | Energy Fuels 2012, 26, 3542-3547