ABSTRACT
In this work, a vortex-assisted dispersive liquid-liquid microextraction method, using an ionic liquid as the extracting solvent was developed, for the simultaneous analysis of three UV filters in different water samples. The extracting and dispersive solvents were selected in a univariate way. Then, the parameters such as the volume of the extracting and dispersive solvents, pH and ionic strength were evaluated using a full experimental design 24, followed by Doehlert matrix. The optimized method consisted of 50 µL of extracting solvent (1-octyl-3-methylimidazolium hexafluorophosphate), 700 µL of dispersive solvent (acetonitrile) and pH of 4.5. When combined with high-performance liquid chromatography, the method limit of detection ranged from 0.3 to 0.6 µg L-1, enrichment factors between 81 and 101%, and the relative standard deviation between 5.8 and 10.0%. The developed method demonstrated effectiveness in concentrating UV filters in both river and seawater samples, being a simple and efficient option for this type of analysis.
ABSTRACT
Biodiesel can be altered when exposed to air, light, temperature, and humidity. Other factors, such as microbial or inorganic agents, also interfere with the quality of the product. In the present work, the Rancimat method and mid-infrared spectroscopy associated with chemometry, were used to identify the oxidation process of biodiesel from different feedstocks and to evaluate the antioxidant activity of butylated hydroxytoluene. The study was carried out in four steps: preparation of biodiesel samples with and without the antioxidant agent, degradation of the samples under the effect of light and heating at 70 °C, measurements of the induction period, obtention of infrared spectra, and multivariate analysis. The Fourier transform mid-infrared spectroscopy was used in combination with multivariate analysis, using techniques such as principal component analysis (PCA) and hierarchical clustering analysis (HCA). The Rancimat results showed that babassu biodiesel has a higher resistance to oxidative degradation, while chicken biodiesel is the most susceptible to degradation; on the other hand, the antioxidant activity was more effective with chicken biodiesel, demonstrating that the antioxidant effect depends on the feedstock used in the production of biodiesel. The oxidative stability of babassu oil-, corn oil-, and chicken fat-based biodiesels decreased during storage both in the presence of light and at high temperature. Prior to PCA, all spectra were pre-processed with a combination of Savitzky-Golay smoothing filter with a 7-point window, baseline correction, and mean-centered data. The use of mid-infrared spectroscopy associated with PCA revealed the first two components to explain the greater variability of data, representing over 75% of total variation for all analyzed systems. In addition, it was able to separate the biodiesel samples according to the fatty acid profile of its feedstock, as well as the type of degradation to which it was subjected, the same being confirmed by HCA.
ABSTRACT
In this work, a liquid-liquid microextraction methodology using solidified floating organic drop (SFODME) was combined with liquid chromatography and UV/Vis detection to determine non-steroidal anti-inflammatory drugs (NSAIDs) naproxen (NPX), diclofenac (DCF), and mefenamic acid (MFN) in tap water, surface water, and seawater samples. Parameters that can influence the efficiency of the process were evaluated, such as the type and volume of the extractor and dispersive solvents, effect of pH, agitation type, and ionic strength. The optimized method showed low detection limits (0.09 to 0.25 µg L-1), satisfactory recovery rates (90 to 116%), and enrichment factors in the range between 149 and 199. SFODME showed simplicity, low cost, speed, and high concentration capacity of the analytes under study. Its use in real samples did not demonstrate a matrix effect that would compromise the effectiveness of the method, being possible to apply it successfully in water samples with different characteristics.
