Multivariate Calibration by Variable Selection for Blends of Raw Soybean Oil/Biodiesel from Different Sources Using Fourier Transform Infrared Spectroscopy (FTIR) Spectra Data Itânia P. Soares, † Thais F. Rezende, † Renzo C. Silva, ‡ Eustáquio Vinícius R. Castro, ‡ and Isabel C. P. Fortes* ,† Laboratório de Ensaio de CombustíVies, Departamento de Química, Instituto de Ciências Exatas, UniVersidade Federal de Minas Gerais, AV. Antônio Carlos, 6627, Campus Pampulha, CEP 31270-901, Belo Horizonte, Minas Gerais, Brazil and Departamento de Química, Instituto de Ciências Exatas, UniVersidade Federal do Espírito Santo, AV. Fernando Ferrari, CEP 29060-900, Vitória, Espírito Santo, Brazil ReceiVed September 5, 2007. ReVised Manuscript ReceiVed January 3, 2008 The partial least-squares (PLS) calibration method as a chemometric tool was used to develop a calibration model using Fourier transform infrared spectroscopy (FTIR) spectra data of biodiesel samples from different sources, such as cotton, castor, and palm, which were mixed with raw soybean oil to simulate an adulteration system. The PLS calibration method was applied with and without variable selection to quantify the amount of raw soybean oil present in these samples. Classic methods of variable selection, such as forward and stepwise, were applied to all origins together and each one separately. Variable selection improves not only the stability of the model to the colinearity in multivariate spectra but also the interpretability of the relationship between the model and the sample composition, which means that it becomes easier to determine and quantify the amount of raw soybean oil mixed in each biodiesel source. 1. Introduction Biodiesel is usually produced by the transesterification of a vegetable oil or animal fat with a short-chain alcohol in the presence of a catalyst. 1,2 Indeed, biodiesel is an interesting alternative fuel because it contributes to a reduction in the emission of CO 2 , which is responsible for the greenhouse effect. SO x and particulate material are also reduced in the combustion process, when compared to conventional fossil fuel. 3 Nowadays, Brazil has the opportunity and challenge to become a worldwide reference as a renewable fuel source producer in the replacement of fossil fuels because of its great area, geographic location, and sunlight. Biodiesel is mainly produced from rapeseed oil in Europe and other countries in the world. In Brazil, there are many oleaginous plants, which could be used in biodiesel production. The climatic diversity favors some oleaginous cultures more in one region than in others. For instance, palm is more common in northern Brazil, while castor is easier to find in the northeast area. Soybean culture develops better in the south and southeast areas. Thus, Brazil has a great potential as world producer and exporter of these raw materials for the respective biofuels. A common use of biodiesel is in blends with conventional mineral diesel fuel. In the European Union (EU), biodiesel is used in a volume fraction of 5% in petrodiesel blends, while in the U.S., energy legislation has mandated the use of at least a volume fraction of 2%. 4 In Brazil, the use of biodiesel has been authorized in 2005 in a volume fraction of 2%. From January 2008, diesel in Brazil must have a volume fraction of 2% biodiesel. One of the challenges of this program is to eliminate the fuel adulteration. Adulteration of fuel, a criminal practice, has been observed in Brazil since the end of monopoly in fuel distribution and introduction market reforms. 5 In the last 5 years, the ANP (Brazilian National Agency for Petroleum, Natural Gas, and Biofuels) has developed efforts to avoid fuel adulterations. In the year 2000, data from ANP have shown that 12.5% of gasoline and 7.3% of diesel samples collected in different localities of the country were not in conformity to the ANP rules for fuel quality. 6 Nowadays, international standard methods, such as EN14103 and ASTM 6584, among others are used to do the quality control of biodiesel. Both methods use gas chromatography as a technique. Results from these analyses can give information about whether or not the sample is adulterated with raw vegetable oils. However, these methodologies have some disadvantages, such as sample preparation, which is time- consuming, use of more than one internal standard, a longer analysis time, and an expensive technique employed. The use of raw vegetable oils directly into engines can cause carbon deposition, injector blocking, and incomplete combustion because of their high viscosities, low volatilities, and polyun- * To whom correspondence should be addressed. Telephone/Fax: 055- 31-3499-6650. E-mail: icpfortes@ufmg.br. † Universidade Federal de Minas Gerais. ‡ Universidade Federal do Espírito Santo. (1) Drown, D. C.; Harper, K.; Frame, E. J. Am. Oil Chem. Soc. 2001, 78, 574–584. (2) Chang, D. Y. Z.; Gerpen, J. H. V. J. Am. Oil Chem. Soc. 1996, 73, 1549–1555. (3) Leung, D. Y. C.; Koo, B. C. P.; Guo, Y. Bioresour. Technol. 2006, 97, 250–256. (4) Pimentel, F. P.; Teixeira, L. S. G.; Ribeiro, G. M. S.; Cruz, R. S.; Stragevitch, L.; Filho, J. G. A. P. Microchem. J. 2006, 82, 201–206. (5) Oliveira, F. C. C.; Brandão, C. R. R.; Ramalho, H. F.; Costa, L. A. F.; Suarez, P. A. Z.; Rubim, J. C. A. Anal. Chim. Acta 2007, 587, 194–199. (6) Knothe, G. J. Am. Oil Chem. Soc. 2001, 78, 1025–1028. Energy & Fuels 2008, 22, 2079–2083 2079 10.1021/ef700531n CCC: $40.75  2008 American Chemical Society Published on Web 02/29/2008