Abstract An electrochemical sensor based on a modified glassy carbon electrode (GCE) with reduced graphene oxide and Ni-Au nanoparticles (Ni(OH)2/AuNp/rGO/GCE) was developed for the determination of ethylene glycol. The graphene oxide was reduced electrochemically at the electrode surface by chronoamperometry, the gold nanoparticles were deposited by chronopotentiometry while the nickel hydroxide nanoparticles were deposited by cyclic voltammetry. The characterization of graphene oxide was performed by Raman spectroscopy, X-ray diffraction (XRD) and transmission-mode scanning electron microscopy (TSEM), while the modified electrodes were characterized by scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) analysis. The determination of ethylene glycol was performed by cyclic voltammetry due to the regeneration of the active sites, preventing loss of the sensor signal. The modified GCE with rGO and Ni(OH)2/AuNp showed a good performance obtaining a linear range of 0.24 to 1.4 mmol L-1 with a correlation coefficient of 0.9903, limits of detection and quantification (49 and 162 µmol L-1, respectively) and high stability with 500 continuous analysis cycles.

Aqueous preparations of the grass Eleusine indica are used for treating malaria and lung infections. Despite its widespread occurrence and therapeutic potential, little is known about its chemical composition. This study reports a common chemical pattern for aqueous extracts of E. indica samples from four different localities, separated from each other by approximately 75 to 1340 km, in a wide variety of abiotic and biotic factors. High-performance liquid chromatography with diode array detection (HPLC-DAD), ultra-performance liquid chromatography with diode array detection and mass spectrometry (UPLC-DAD-MS/MS), and nuclear magnetic resonance (NMR) were the analytical techniques applied to characterize substances from E. indica, from each locality. Principal component analysis (PCA) confirmed that E. indica specimens came from four different localities. However, all of the four populations showed a common peaks pattern. This is the first chemical profile report of E. indica. Moreover, p-coumaric acid and isoschaftoside were characterized for the first time in this species.

The volatile compounds formed by thermal degradation of the carotenoids present in Dunaliella bardawil were investigated by microwave irradiation (MW) and water bath heating (WB) in different conditions of temperature and time using central composite design. Volatiles extraction by solid phase microextraction (SPME) was optimized and performed at 40 °C for 15 minutes, and those in greater amount were quantified by a validated method of gas chromatography coupled to a quadrupole mass spectrometer (GC-qMS). Employing WB, 10, 12 and 120 ng mL-1 of β-cyclocitral, α-ionone e β-ionone, respectively, were obtained between 60 and 87 °C for 30-75 min, while by MW, 5, 5, 50 ng mL-1 were obtained between 75-107 °C for 1.5-2.8 min. Considering the shorter time of MW, it can be concluded that if the time necessary to obtain the best yield by WB is employed in multiple MW cycles, an amount 10 times greater of those compounds would be obtained by MW than by WB. The results suggest a new biotechnology application for the carotenoids of the microalgae of the Dunaliella genus.