Several methods exist for determining soil organic carbon, and each one has its own advantages and limitations. Consequently, a comparison of the experimental results obtained when these methods are employed is hampered, causing problems in the comparison of carbon stocks in soils. This study aimed at evaluating the analytical procedures used in the determination of carbon and their relationships with soil mineralogy and texture. Wet combustion methods, including Walkley-Black, Mebius and Colorimetric determination as well as dry combustion methods, such as Elemental and Gravimetric Analysis were used. Quantitative textural and mineralogical (kaolinite, goethite and gibbsite) analyses were also carried out. The wet digestion methods underestimated the concentration of organic carbon, while the gravimetric method overestimated. Soil mineralogy interfered with the determination of carbon, with emphasis on the gravimetric method that was greatly influenced by gibbsite.

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The purpose of this study was to evaluate the essential oil composition and yield from leaves of two Brazilian species (Myracrodruon urundeuvaandBlepharocalyx salicifolius) harvested during daytime. Essential oils were obtained by steam distillation and had their yield determined.Blepharocalyx salicifoliuspresented yields of 0.049% (9 a.m.), 0.045% (1 p.m.), and 0.069% (5 p.m.). ForMyracrodruon urundeuva, we found 0.13% (9 a.m.), 0.11% (1 p.m.), and 0.08% (5 p.m.). Finally, compound identification and quantification were carried out by GC-MS and GC-FID techniques, respectively. Thirteen major compounds were identified forBlepharocalyx salicifolius, representing 91.6% of the EOs, of whichp-cymene (25.9%) was detected as amajor component. Nine major compounds were identified forMyracrodruon urundeuva, representing 90.3% of the EOs, whereasβ-myrcene showed the greatest concentration (66.4%).

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In recent years, ecstasy trafficking has grown in complexity and tablets has been commonly sold containing different contents of 3,4-methylenedioxymethamphetamine (MDMA) or even other psychoactive substances. In contrast, identification and quantification of drugs of abuse is still a challenge, once the access to drug standards is very restricted in Brazil. In this work, ecstasy tablets seized by the Brazilian Federal Police have their chemical composition identified and quantified by gas chromatography and quantitative 1 H nuclear magnetic resonance based on an internal standard approach (IS-1 H-qNMR). Both methods were validated and showed suitable results for the figures of merit. IS-1 H-qNMR shows excellent results of accuracy (relative error < 5%) and precision (relative standard deviation (RSD) < 2%). Comparatively, IS-1 H-qNMR is more efficient and versatile than gas chromatography to accomplish in a single analysis the identification and quantification of target analytes. Since the method does not require a specific reference material, it is cost effective and provides agility to routine forensic analysis.