Determination of polybrominated diphenyl ethers in milk samples. Development of green extraction coupled techniques for sample preparation

Ultrasound‐assisted extraction (UAE), cloud point extraction (CPE), and ultrasound back‐extraction (UABE) techniques have been coupled for lixiviation, preconcentration, and cleanup of polybrominated diphenyl ethers (PBDEs) from milk samples for determination by gas chromatography‐electron capture detection (GC‐ECD). Physicochemical parameters that affect the efficiency of the extraction system were investigated using a design of experiments based on multivariate statistical tools, and considering the sample matrix along the development. The coupling of the leaching step, UAE, enhanced ca. 3.5 times the extraction efficiency of the former sample preparation methodology (CPE‐UABE) leading to cleaner sample extracts suitable for GC analysis. Under optimum conditions, the proposed methodology exhibits successful performance in terms of linearity and precision, with recoveries in the range of 68–70% and LODs within the range 0.05–0.5 ng/g dry weight (d.w.). The proposed sample preparation methodology coupled three green analytical techniques. It expands the application frontiers of CPE for the analysis of biological samples by GC. The optimized methodology was used for determination of PBDEs in powder milk samples, from both commercial and human sources.     

Dispersive liquid–liquid microextraction of quinolones in porcine blood: Validation of a CE method using univariate calibration or multivariate curve resolution‐alternating least squares for overlapped peaks

In the previously published part of this study, we detailed a novel strategy based on dispersive liquid–liquid microextraction to extract and preconcentrate nine fluoroquinolones in porcine blood. Moreover, we presented the optimized experimental conditions to obtain complete CE separation between target analytes. Consequently, this second part reports the validation of the developed method to determine flumenique, difloxacin, enrofloxacin, marbofloxacin, ofloxacin, ciprofloxacin, through univariate calibration, and enoxacin, danofloxacin, and gatifloxacin through multivariate curve resolution analysis. The validation was performed according to FDA guidelines for bioanalytical assay procedures and the European Directive 2002/657 to demonstrate that the results are reliable. The method was applied for the determination of fluoroquinolones in real samples. Results indicated a high selectivity and excellent precision characteristics, with RSD less than 11.9% in the concentrations, in intra‐ and interassay precision studies. Linearity was proved for a range from 4.00 to 30.00 mg/L and the recovery has been investigated at four different fortification levels, from 89 to 113%. Several approaches found in the literature were used to determinate the LODs and LOQs. Though all strategies used were appropriate, we obtained different values when using different methods. Estimating the S/N ratio with the mean noise level in the migration time of each fluoroquinolones turned out as the best studied method for evaluating the LODs and LOQs, and the values were in a range of 1.55 to 4.55 mg/L and 5.17 to 9.62 mg/L, respectively.     

Effects of modified starch and fat on the rheological characteristics of newly formulated processed cheese: Use of experimental design method

This study aims to investigate the impact of the incorporation of starch (modified and non-modified) on the texture of the processed cheese in order to appreciate a new recipe on one hand and to try to reduce fat content (FC) on the other. The modeling of the experimental results has been performed. An experimental design was used (the variable factors are the amount of starch and FC). The dry extract (DE) of cheese and parameters derived from the modeling of rheological results are the selected responses. The cheese with a concentration of modified starch that is greater than 2% has a high viscosity at rest, while the cheese with non-modified starch has a lower viscosity. When the FC exceeds 15%, the viscosity increases as the concentration of the starch exceeds 2%. Below this concentration, the FC effect is negligible except when the starch concentration is 1%, in this case the viscosity decreases.     

石墨烯导热性能及其测试方法

石墨烯以其独特的结构和优异的性能引起人们广泛的关注。本文通过总结近期国内外石墨烯导热工作研究进展,梳理了石墨烯的导热机理,根据导热机理指出缺陷、基底、石墨烯边缘是影响石墨烯热导率的主要因素。综述了采用分子动力学及非平衡态格林函数方法进行石墨烯热导率模型计算的研究成果,并在模型的基础上,全面阐述了实验方面针对不同层数石墨烯热导率的测试方法及结果。     

Metastable flow in capillary tubes: An experimental evaluation

This work presents the results of an experimental study with pure refrigerants R-134a and R-600a and refrigerant–oil mixtures flowing through capillary tubes in order to analyse the metastable flow. A large number of experiments were carried out to verify the influence of several variables on the underpressure of vaporization, mainly the inlet subcooling, internal diameter and inlet pressure. Capillary tubes with internal diameter of 0.69 mm and 0.82 mm were tested for condensation temperatures between 40 °C and 50 °C and subcooling degrees between 3 °C and 12 °C. Measurements for oil concentrations of 1% and 3% were conducted and compared with those for pure refrigerant R-134a. The oil influence on the metastable flow was tested and the effect on the underpressure of vaporization is addressed for lower oil concentrations.     

Synthesis and applications of a chiral-oxygenated 3-chloro-3,6-dihydro-2H-pyran obtained under Overman rearrangement conditions

A chlorinated side product was formed under Overman rearrangement conditions from a trichloroacetimidate along with the expected allylic amide. The chlorinated product derived from a hex-2-enopyranoside was obtained in a totally stereoselective manner, and it can be a useful synthetic intermediate for chlorinated sugars. In order to improve the isolated yields of either the expected Overman rearrangement product or the chlorinated compound, we carried out a thorough study on the experimental conditions. The application of the latter for the synthesis of potential calpain inhibitors is also reported.     

Experimental design in the optimization of a microwave acid digestion procedure for the determination of metals in biomorphic ceramic samples by inductively coupled plasma mass spectrometry and atomic absorption spectrometry

In the present paper, we have synthesized a biomorphic ceramic material from oak wood as biological template structure and infiltration with zirconia-sol. After the material characterization, we have optimized the sample dissolution by acid attack in an oven under microwave irradiation. Experimental designs were used as a multivariate strategy for the effect's evaluation of varying several variables. This article describes the development by response surface methodology (RSM) of a procedure for zirconium determination, and other ions, such as copper and nickel by inductively coupled plasma mass spectrometry (ICP-MS) and others, such as iron, calcium and magnesium determination by flame atomic absorption spectrometry (FAAS) in the synthesized sample after digestion. A full factorial design (3³) was used to find optimal conditions for the procedure through response surface study. Three variables (time, HNO₃ volume and HF volume) were regarded as factors and as response to the concentration of different metal ions in the optimization study.     

Optimum extraction process of polyphenols from Bridelia grandis stem bark using experimental design

Euphorbiaceae barks are known to contain an appreciable amount of polyphenolic compounds responsible for several biological activities. Preliminary extraction from Bridelia grandis stem bark afforded high content of polyphenols, determined by spectrophotometric methods such as Folin–Ciocalteu (for total phenols, TP) and n‐butanol‐HCl (for condensed tannins, CT). A preliminary Plackett–Burman screening design was used to identify the key factors that influence the TP and CT extraction. Between all the variables known to influence the extraction from vegetable matrixes, six were selected; maceration was chosen as traditional extraction methodology. To investigate the effect of solvents and extraction method, methanol, acetone 70% (v/v in water), centrifugation and ultrasound were chosen. A full factorial design 2³ was applied to optimize the extraction procedure. The responses were obtained analyzing the extracts for their TP and CT contents determined by the above‐mentioned spectrophotometric methods. The results confirm that, within the explored domain, the optimum solvent is methanol and the optimum method is one‐cycle centrifugation. Finally, it was also compared with the effect of maceration on the considered responses. It has never given results better than centrifugation, whereas in the case of CT it represents an advantage to employ a three‐cycle centrifugation instead of one.     

A new thermally immobilized fluorinated stationary phase for RP‐HPLC

A new fluorinated stationary phase was prepared through thermal immobilization of poly(methyl‐3,3,3‐trifluoropropylsiloxane) onto 5 μm Kromasil silica particles. The best conditions of immobilization time and temperature were determined through a central composite design and response surface methodologies. Physical–chemical characterization using solid‐state ²⁹Si NMR measurements, infrared spectroscopy and elemental analysis showed that the immobilization process was effective to promote a coating of the support that corresponds to a monolayer of polymer. The stationary phase presents selectivity for positional isomers and good peak shape for basic compounds.     

Sorbent trapping solid-phase microextraction of fragrance allergens in indoor air

Exposure to fragrance substances is exponentially increasing in our daily life due to the enhanced use of scented products. Some fragrances are known to be important sensitizers, inhalation being an important exposure pathway in indoor environments. A simple and sensitive method based on solid-phase enrichment and solid-phase microextraction (SPME) followed by gas chromatography–mass spectrometry (GC–MS) has been developed for the analysis of 24 volatile fragrance allergens in indoor air. Suspected allergens present in the air (0.2 m³) were adsorbed onto a very small quantity of florisil (25 mg) and then transferred to a SPME fiber in the headspace mode (HS). To the best of our knowledge, this paper describes the first application of SPME for the determination of these compounds in air samples. The experimental parameters affecting the microextraction process have been optimized using a multifactor experimental design strategy. Accuracy, linearity, precision and detection limits (LODs) were evaluated to assess the performance of the proposed method. External calibration, using spiked sorbent standards, and not requiring the complete sampling process (only the SPME step), demonstrated to be suitable for the quantification of all suspected allergens. Recovery studies were performed at three concentration levels (0.04, 1.00 and 50 μg m⁻³), obtaining quantitative recoveries (≥85%) in most cases. LOD values at the low ng m⁻³ level were achieved for all the target compounds. The application of the method to daily home air samples demonstrated the ubiquity of this kind of fragrance ingredients in quotidian indoor environments, finding 18 of the 24 considered compounds in concentrations ranging from 0.01 to 56 μg m⁻³. Benzyl alcohol, linalool, citronellol, ionone and lilial were found in most analyzed samples.