Simple and selective extraction of quercetin with microextraction in packed syringe method using modified glass powder by a molecularly imprinted polymer followed by spectrophotometric determination

A new sample preparation method based on microextraction in packed syringe was developed for preconcentration of quercetin prior to its spectrophotometric determination. Molecularly imprinted polymers as packing material was used for higher extraction efficiency. First, glass powder as support material because of low cost and available substrate was modified, and then molecularly imprinted polymers were synthesized by the sol–gel method using 3-aminopropyltriethoxysilane as a functional monomer and tetraethyl orthosilicate as cross-linker agent. The combination of a molecularly imprinted polymers and microextraction in packed syringe increased the selectivity and sensitivity. The surface morphology and functionality of the prepared molecularly imprinted polymers was characterized using Fourier-transform infrared spectroscopy, Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and thermogravimetric analysis. Different influencing parameters on extraction efficiency such as effect of the number of sample sorption/desorption cycles, type and volume of desorption solvent, pH of the sample solution, and molecularly imprinted polymers amounts were optimized. Under the optimum condition, the proposed method displayed a linear range from 0.01 to 5 µg mL⁻¹ and limit of detection 3.68 ng mL⁻¹. Relative standard deviation for three replicate determination of 1 µg mL⁻¹ quercetin was 2.1 %. The proposed method was applied successfully for the selective extraction of quercetin from tea and coffee samples.     

Poly(ortho‐toluidine) Modified Carbon Paste Electrode: A Sensor for Electrocatalytic Reduction of Nitrite

The electrocatalytic reduction of nitrite has been studied by poly(ortho‐toluidine) films modified carbon paste electrode (P‐OT/MCPE). Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of poly(ortho‐toluidine) as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the reduction of nitrite occurs at a potential about 600 mV more positive than unmodified carbon paste electrode. The catalytic reaction rate constant, (k_h), was calculated 8.68×10² M^?1 s^?1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00×10^?4 M–1.90×10^?2 M. Detection limit has been found to be 3.38×10^?4 M (2σ). This method has been successfully employed for quantification of nitrite in real sample.     

Self-affine and ARX-models zonation of well logging data

Zonation of time series into models which their parameters are piecewise constant are important and well-studied problems. Geophysical well logging data often show a complex pattern due to their multifractal nature. In a multifractal system, any pieces of it are established by a distinct exponent that can characterize them. This feature has the capability to cluster them. Self-affine zonation by Auto Regressive model with exogenous inputs (ARX) is a new approach which places well logging segments in the clusters which are more self-affine against the other clusters. This approach was performed and compared with a conventional ARX zonation in the well logging data of three different oilfields in southern parts of Iran. The results showed a good accuracy for detecting homogeneous lithological segments and led to a precise interpretation process to update the reservoir architecture.     

Three-Component Reaction for an Efficient Synthesis of Stable Phosphorus Ylides Using Mercapto Compounds

Stabilized phosphorus ylides were obtained from the three-component reaction between dialkyl acetylenedicarboxylate and sulfur compounds such as pyridine-2-thione, 2-furylmethanethiol, ethanedithioamide, and N-phenyl-1,2,4-triazole-3-thiol in the presence of triphenylphosphine in excellent yields.     

Optimization of the oxalate catalyzed photoelectro-Fenton process under visible light for removal of Reactive Red 195 using a carbon paper cathode

The decolorization of Reactive Red 195 (RR195) by the oxalate catalyzed photoelectro-Fenton (PEF) process using carbon paper electrode as a cathode under visible light was studied. Comparison between electro-Fenton (EF), PEF, and PEF/oxalate processes for the removal of RR195 showed that color removal follows in decreasing order: PEF/oxalate > PEF > EF. Response surface methodology (RSM) was used to determine the effects of the four main independent parameters (initial dye, oxalate and Fe³⁺ concentrations, and reaction time) on decolorization efficiency. A high coefficient of determination value (R ² = 0.963) has resulted from the analysis of variance (ANOVA). The optimum values of the initial Fe³⁺ concentration, the initial amount of oxalate, the initial dye concentration, and the reaction time were found to be 0.3 mM, 0.6 mM, 20 mg/L, and 120 min, respectively. A high decolorization efficiency (>93 %) was experimentally obtained for RR195 under the established optimum conditions. The response surface plots were employed to establish the effect of experimental parameters on the decolorization efficiency. These results clearly indicated the success of RSM as a suitable method for optimizing the operating conditions. The mineralization of the dye was investigated by total organic carbon (TOC) measurement. 96.2 % mineralization of 50 mg/L RR195 was observed at 9 h.