Three different calibration curves based on (1)H-NMR spectroscopy (300 MHz) were used for quantifying the reaction yield during biodiesel synthesis by esterification of fatty acids mixtures and methanol. For this purpose, the integrated intensities of the hydrogens of the ester methoxy group (3.67 ppm) were correlated with the areas related to the various protons of the alkyl chain (olefinic hydrogens: 5.30-5.46 ppm; aliphatic: 2.67-2.78 ppm, 2.30 ppm, 1.96-2.12 ppm, 1.56-1.68 ppm, 1.22-1.42 ppm, 0.98 ppm, and 0.84-0.92 ppm). The first curve was obtained using the peaks relating the olefinic hydrogens, a second with the parafinic protons and the third curve using the integrated intensities of all the hydrogens. A total of 35 samples were examined: 25 samples to build the three different calibration curves and ten samples to serve as external validation samples. The results showed no statistical differences among the three methods, and all presented prediction errors less than 2.45% with a co-efficient of variation (CV) of 4.66%.
The official method for analyzing N-nitrosoglyphosate (NNG), a relevant impurity, in glyphosate matrix demands complicated instrumentation and operating conditions not available in many laboratories. In this work, we developed a direct, simple, selective and sensitive ion chromatography (IC) method with UV detection for the determination of NNG in samples of technical glyphosate. To separate NNG from the matrix we used an IC anionic column mounted in a high-performance liquid chromatography (HPLC) apparatus equipped with a photo-diode array detector. The system used a high ionic strength eluent. The method was validated, taking into account the following figures of merit: selectivity, linearity, repeatability, intermediate precision, recovery, limit of detection (LOD), and limit of quantification (LOQ). The proposed method is sensitive enough to quantify NNG below the maximum concentration determined by both the Food and Agricultural Organization of the United Nations (FAO) and the Brazilian regulation.
The compilation of forensic reports from pesticides seized by the Federal Police in Brazil showed that metsulfuron-methyl, imidacloprid, fipronil, tebuconazole, clorimuron-ether and glyphosate were the dominant active ingredients (AI) illegally imported. Despite these AI were not among the most traded pesticides in Brazil, high prices of corresponding legal formulations may stimulate this illegal activity. Based on this study, smuggled pesticides containing tebuconazole and metsulfuron-methyl were seized and quantitatively analyzed using gas and liquid chromatography, respectively. Tebuconazole results, in liquid and solid presentations, were in accordance with the information on the label, while most metsulfuron-methyl samples, labeled as 600 g kg-1, showed lower concentrations in chemical analysis (mean of 337.0 g kg-1 + 2.0).
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