Two different gold-silica-based nanomaterials were prepared: (i) silica-supported gold nanoparticles (AuNP/SiO2); and (ii) gold-silica core-shell nanoparticles (AuNP@SiO2). Three strategies for sample treatment (S), consisting in acid treatments, were employed: (S1) HNO3; (S2) HNO3 + HCl; and (S3) HF + HNO3 + HCl, applying microwave oven digestion for S2 and S3. From three calibration curves, slope, intercept, and linear correlation coefficient were obtained. The accuracy of the methods was evaluated by comparing the gold contents in a sample determined by flame atomic absorption spectrometry (FAAS) and by inductively coupled plasma atomic emission spectrometry (ICP-OES). Finally, the amount of gold for all samples was determined by FAAS. UV-Vis spectroscopy and transmission electron microscopy (TEM) were used to compare the material before and after sample treatment. By comparison, the application of S2 and S3 allowed the presence of gold on or in the silica matrix to be determined and the amount quantified.

The optimized analytical methodology described herein is based on an ion exchange column and an H3PO4 solution (pH 2.24) as the mobile phase, with a flow rate of 0.4 mL min-1 and refractive index detection (RID). On applying the methodology, it was possible to identify 7 products obtained from the oxidation of glycerol with an analysis time of 27 min. The developed method was validated through the evaluation of a series of analytical parameters. The results obtained were evaluated considering the peak area and peak height. The analytical curves showed a correlation coefficient of ≥ 0.986. The coefficient of variation values obtained were ≤ 3.60% for instrumental precision, ≤ 19.36% for intermediate precision in LOQ (1.25 µg mL-1) and ≤ 17.93% for repeatability in LOQ (1.25 µg mL-1) and different days. The limit of quantification established for all compounds was 1.25 µg mL-1 obtained through the parameters of the analytical curve. The accuracy of the method showed recovery values of 85.6 to 112.3% for real fortified sample at 3 concentration levels. Two different samples of glycerol oxidation products were applied to the validated methodology; one obtained from AuNP/SiO2 as catalyst (conversion of 62.42%), and other using AuNP/MWCNT (conversion of 89.5%).

In this study an analytical method, based on gas chromatography with flame ionization detection, using a short column and response factor (GCSCRF), was validated for the quantification of fatty acid alkyl esters (methylic or ethylic). During the validation process, the proposed method was employed to analyze twenty samples of fatty acid methyl esters and fatty acid ethyl esters. Biodiesel samples were produced from soybean oil and the validated method was found to be selective, being able to separate and identify every ester species present in the samples according to its carbon number. When the method was submitted to some variations in the sample preparation procedure, it remained robust. Limits of detection and quantification were 6.76 and 20.4 mg mL-1, respectively. The suggested method also showed great precision when successive analyses were carried out for different analysts, with standard deviation (SD) 0.6 for repeatibility and relative standard deviation (RSD) percentage 7.3% for intermediate precision, excellent accuracy when compared to other reference methods (EN 14103 and high-performance liquid chromatography with ultraviolet dection (HPLC-UV)) and recovery studies.

The growth of biodiesel market and the implementation of regulations related to biodiesel production and biodiesel/diesel blending has encouraged the development of appropriate analytical methods to control the composition of this type of mixture. In this study, an evaluation of the potential of GC×GC for the characterization of samples of beef tallow biodiesel and the composition of blends of biodiesel/diesel is presented. The methodology was applied to beef tallow biodiesel and its mixtures with petrodiesel, ranging from B2 to B50. Results allowed not only the identification and quantification of the biodiesel esters, but also the biodiesel percentage in biodiesel/diesel blends.