This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.

Um método analítico por cromatografia líquida de alto rendimento com detecção ultravioleta (HPLC-UV) (método A) foi utilizado na determinação simultânea dos valores totais de triacilglicerídeos, diacilglicerídeos, monoacilglicerídeos e ésteres metílicos de ácidos graxos na alcólise de diferentes óleos (algodão, canola, girassol, milho e soja). As análises foram realizadas a 40 °C por 20 min usando gradiente de metanol (MeOH) e 2-propanol-hexano 5:4 (v/v) (PrHex): 100% de MeOH em 0 min, 50% de MeOH e 50% de PrHex em 10 min mantido com eluição isocrática por 10 min. Outro método por HPLC-UV (método B) com eluição isocrática de acetonitrila por 34 min foi utilizado na determinação da composição de ácidos graxos de óleos analisando seus derivados de éster metílico. Os conteúdos foram analisados com satisfatória repetibilidade (desvio padrão relativo, RSD < 3%), linearidade (r 2 > 0,99) e sensibilidade (limite de quantificação). O método B foi comparado com o método oficial cromatográfico gasoso com detecção através de ionização por chama (GC-FID) da American Oil Chemists' Society (AOCS) na determinação de ésteres metílicos de ácidos graxos (FAME) em amostras reais de biodiesel.An analytical method using high performance liquid chromatography with UV detection (HPLC-UV) (method A) was used for simultaneous determination of total amounts of triacylglycerides, diacylglycerides, monoacylglycerides and fatty acid methyl esters in alcoholysis of different oil (cotton, canola, sunflower, corn and soybean) samples. Analyses were carried out at 40 °C for 20 min using a gradient of methanol (MeOH) and 2-propanol-hexane 5:4 (v/v) (PrHex): 100% of MeOH in 0 min, 50% of MeOH and 50% of PrHex in 10 min maintained with isocratic elution for 10 min. Another HPLC-UV method (method B) with acetonitrile isocratic elution for 34 min was used to determine the fatty acid composition of oils analyzing their methyl ester derivatives. Contents were determined with satisfactory repeatability (relative standard deviation, RSD < 3%), linearity (r 2 > 0.99) and sensitivity (limit of quantification). Method B was compared with an official gas chromatographic method with flame ionization detection (GC-FID) from American Oil Chemists' Society (AOCS) in the determination of fatty acid methyl esters (FAME) in biodiesel real samples.Keywords: biodiesel, triacylglycerides, gas chromatography, liquid chromatography, methyl ester IntroductionThe direct use of fats and oils (mainly composed by triacylglycerides) in diesel engines is problematic and can lead to many problems, such as carbon deposit due to its poor atomization, high viscosity and thickening of lubricating oil as a consequence of its low volatility. 1,2 There are many possible solutions to address the viscosity problem, which are dilution with diesel fuel, microemulsions with short chain alcohols and pyrolysis or transesterification of triacylglycerides. Transesterification is a widespread process used for obtaining biodiesel and involves the catalyzed reaction of triacylglycerides (TAGs) a...

An important drawback to be overcome in biodiesel technology is its low oxidative stability. One approach to improve the oxidative stability of soybean oil biodiesel is the partial hydrogenation of double bonds. In the current work, an efficient two-phase catalytic system using palladium acetate dissolved in BMIÁBF 4 ionic liquid to an in situ generation of palladium nanoparticles was developed in order to promote a selective hydrogenation reaction. Upon using this catalytic system it was possible to partially hydrogenate biodiesel into mono-hydrogenated compounds avoiding the formation of saturated compounds. The nanoparticulate system was compared with the traditional heterogeneous Pd/C system and gave far higher selectivity. It was possible to recover and reuse the ionic phase containing the catalyst up to three times without significant loss in its catalytic performance. Indeed, atomic absorption spectroscopy showed an excellent reclaim of the catalyst, which stayed in the ionic phase. Several parameters, such as temperature, hydrogen pressure, metal concentration and reaction time, were also evaluated.