Biodiesel fuel (fatty acid esters) has become more and more attractive due to its environmental benefits. Transesterification is the most common and important method for making biodiesel from vegetable oils or animal fats. Several studies have focused on the development and improvement of analytical methods for monitoring biodiesel production and determining the fuel quality. Analytical procedures reported in the literature include chromatographic methods (e.g., gas chromatography, high-performance liquid chromatography, gel permeation chromatography, etc.) and spectroscopic methods [e.g., 1H and 13C NMR, near infrared, Fourier transform infrared spectroscopy, and recently, Fourier transform (FT)-Raman]. The study presented in this paper expands our previous research, in which FT-Raman spectroscopy combined with partial least squares (PLS) multivariate analysis was successfully applied to the quantification of soybean oil/ethyl ester mixtures. The FT-Raman/PLS methods developed by our group were used to monitor and quantify a transesterification reaction process involving soybean oil and ethanol to produce fatty acid ethyl esters (biodiesel) over 22 h catalyzed by a heterogeneous Lewis acid catalyst. The results were successfully correlated with two 1H NMR spectroscopic methods reported in the literature and a new 1H NMR method proposed in this work that can be easily extended to other vegetable oils. The correlation coefficients (R 2) obtained from the linear fit between FT-Raman measurements and the above 1H NMR methods were 0.9974, 0.9847, and 0.9972, respectively.

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...

No abstract

SummaryThe egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short‐range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10‐trimethyltridecanoate, a male‐produced pheromone of E. heros.Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long‐range kairomones, by T. podisi, is discussed.Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10‐trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short‐range kairomone.Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.

No abstract