Renata Pereira Lopes

Development and validation of an efficient and innovative method for the quantification of multiclass veterinary drugs in milk by using LC–MS/MS analysis

An efficient analytical method for the simultaneous quantification of 27 veterinary drugs from five different classes (benzimidazoles, betalactams, quinolones, sulfonamides and tetracyclines) in bovine milk using a novel extraction procedure (liquid–liquid extraction with fast partition at very low temperature) and liquid chromatography coupled to tandem mass spectrometry is described. The full analytical method was validated according to Brazilian legislation (normative instruction SDA/MAPA 24/2009) and suitable values were achieved for all the parameters evaluated. Hence, the recoveries were within the established ranges (>70%), except for sulfathiazole (67.4% at the 0.5 × MRL level) and marbofloxacin and thiabendazole (112.5 and 114.6% respectively, at the 1.0 × MRL level). The repeatability and intermediate precision for all the analytes, expressed as relative standard deviations, were lower than 20 and 25%, respectively. The decision limits (CCα), detection capabilities (CCβ) and expanded uncertainties were also calculated and satisfactory results were obtained. Finally, the method was applied to 15 actual samples and traces of oxytetracycline and sulfamethazine were detected in three of them.

Sulfentrazone dechlorination by iron-nickel bimetallic nanoparticles ☆

The sulfentrazone dechlorination using bimetallic nanoparticles of Fe/Ni was studied. Different variables that could influence the sulfentrazone conversion were investigated, such as nitrogen atmosphere, pH and dosage of the nanoparticles and initial concentration of sulfentrazone. The best results were obtained using controlled pH (pH 4.0) and 1.0 g L(-1) of nanomaterials, resulting in 100 % conversion in only 30 min. Kinetic studies were also conducted, evaluating the influence of different nanoparticle dosages (1.0 to 4.0 g L(-1)), system temperatures (20 to 35 °C) and nickel levels in the composition of the nanomaterials (0.025 to 0.10 gNi/gFe). The mechanism of sulfentrazone conversion has changed due a direct reduction on the catalytic activity sites and indirect reduction by atomic hydrogen. Both mechanisms have followed pseudo-first order models. The conversion rate improved when the dosage of the nanomaterials, system temperature and nickel content in the composition of the nanocomposites were increased. Finally, the conversion products were elucidated by mass spectrometry and toxicity assays were performed using Daphnia Similis. The results showed that the dechlorination product is less toxic than sulfentrazone.

Degradation of the Reactive Blue 4 Dye in Aqueous Solution Using Zero-Valent Copper Nanoparticles

The degradation of the Reactive Blue 4 (RB4) dye by zero-valent copper nanoparticles (nZVC) was investigated. Degradation rates of approximately 90% were reached within 10 minutes of reaction. Total Organic Carbon (TOC) analysis shows that the dye molecules undergo mineralization, therefore indicating the degradation process is oxidative. Experimental tests, held in the presence of tertiary butyl alcohol, acting as a hydroxyl radicals ) captor, and copper (I) oxide, demonstrated that the reaction mechanism is governed by the concentration of Cu (I) instead of . The second-order kinetics model was the most appropriate one to explain the experimental data. Higher values of the reaction rate constant were obtained in higher temperatures and higher nZVC doses and in lower RB4 initial concentrations. The initial pH in more acidic conditions (3 and 4) was kinetically more favorable to the degradation reaction; the activation energy was estimated to be 42 kJ mol−1 based on calculations using the experimental data. Finally, the recovered nanoparticles were utilized on a new reaction cycle, showing a small loss of their efficiency and catalytic activity.

DIRECT INFUSION ESI-MS APPLIED IN THE DETECTION OF BYPRODUCTS DUE TO REDUCTIVE DEGRADATION OF ACETAMIPRID BY ZERO-VALENT IRON

This study investigated the reductive degradation of acetamiprid (5 mg L-1) in aqueous medium (at pH 2.0) induced by zero-valent iron (50 mg). The process was monitored using high-performance liquid chromatography (HPLC) to determine the degradation rate as a function of reaction time, and direct infusion electrospray ionization mass spectrometry (DI-ESI-MS) to search for (and potentially characterize) any possible byproducts formed during degradation. The results obtained via HPLC showed that after 60 min, the degradation of the substrate reached nearly 100% in an acidic medium, whereas the mineralization rate (as determined by total organic carbon measurements) was as low as 3%. Data obtained by DI-ESI-MS showed that byproducts were formed mainly by insertions of hydrogen atoms into the nitrile, imine, and pyridine ring moieties, in addition to the observation of chlorine substitution by hydrogen replacement (hydrodechlorination) reactions.