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A novel in vivo design was used in combination with solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) to characterize the volatile compounds from the skin secretion of two species of tree frogs. Conventional SPME-GC/MS also was used for the analysis of volatiles present in skin samples and for the analysis of volatiles present in the diet and terraria. In total, 40 and 37 compounds were identified in the secretion of Hypsiboas pulchellus and H. riojanus, respectively, of which, 35 were common to both species. Aliphatic aldehydes, a low molecular weight alkadiene, an aromatic alcohol, and other aromatics, ketones, a methoxy pyrazine, sulfur containing compounds, and hemiterpenes are reported here for the first time in anurans. Most of the aliphatic compounds seem to be biosynthesized by the frogs following different metabolic pathways, whereas aromatics and monoterpenes are most likely sequestered from environmental sources. The characteristic smell of the secretion of H. pulchellus described by herpetologists as skunk-like or herbaceous is explained by a complex blend of different odoriferous components. The possible role of the volatiles found in H. pulchellus and H. riojanus is discussed in the context of previous hypotheses about the biological function of volatile secretions in frogs (e.g., sex pheromones, defense secretions against predators, mosquito repellents).

An alternative method for the determination of calcium and magnesium in biodiesel samples by flame atomic absorption spectrometry (FAAS) is proposed. The samples were prepared as water-in-oil microemulsions, and aqueous standards microemulsified in the same way were used for calibration. A study of long-term stability shows that the analytes remained stable in the microemulsions for at least 5 days. To assess the accuracy of the results, other methods were applied, such as recovery tests, as well as a comparison to the Brazilian Standard Method ABNT NBR 15556, which consists of the sample dilution with an organic solvent and a determination by FAAS. Limits of detection (LOD) of 0.04 and 0.1 μg g-1 and characteristic concentrations of 30 and 6 μg L-1 were obtained for calcium and magnesium, respectively. The method showed better LODs and precision in relation to dilution with organic solvent. The results obtained were statistically in agreement with those obtained with the Brazilian Standard Method at a 95% confidence level, and the recovery tests presented values between 92 and 117% for biodiesel samples. The main advantages observed in relation to the dilution method were the use of inorganic standards in the microemulsions for calibration, no use of carcinogenic organic solvents, and the higher stability of the analytes, besides the higher sensitivity. These advantages make the proposed method more appropriate for biodiesel routine analysis. The method was also tested for vegetable oil analysis.

The human nose has been used as a detector in gas chromatography analysis to evaluate odoriferous compounds related to aroma and quality of wine. Several olfactometric techniques are available to access the description, intensity, and/or duration of the odor of each compound. Olfactometry can be associated with one‐dimensional gas chromatography or multidimensional gas chromatography, including heart‐cut gas chromatography and comprehensive two‐dimensional gas chromatography. Multidimensional gas chromatography may help to resolve coeluted compounds and detect important trace components for the aroma. The identification of odor‐active compounds may help to differentiate wines according to terroir, grapes cultivars used in winemaking or types of aging, understand the role of fungal infection of grapes for wine quality, find the best management practices in vineyard and vinification to obtain the greatest quality. In addition, when the instrumental techniques are combined with sensory analysis, even more accurate information may be obtained regarding the overall wine aroma. This review discloses the state of the art of olfactometric methods and the analytical techniques used to investigate odor‐active compounds such as one‐dimensional gas chromatography, multidimensional gas chromatography, and comprehensive two‐dimensional gas chromatography. The advances in knowledge of wine aroma achieved with the use of these techniques in the target and profiling approaches were also discussed.

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