Effervescence-assisted dispersive liquid-liquid microextraction based on deep eutectic solvent for preconcentration and FAAS determination of copper in aqueous samples

A new effervescence-assisted dispersive liquid-liquid microextraction, EA-DLLME, technique was developed for preconcentration and flame atomic absorption spectrometric determination of copper in aqueous samples. Effervescence assistance and DES combination for metal ion extraction was used for the first time. In the presented study, six different effervescence powders were examined to achieve maximum extraction efficiency. In addition, 1,5 diphenyl carbazide was used as complexing agent and DES prepared by mixing choline chloride and phenol was used as extraction solvent. The effect of several parameters such as pH, concentration of complexing agent, composition and volume of DES, amount of THF, composition and amount of effervescent agent were examined. Performed experiments showed that optimum pH was 6.0, the best effervesce powder composition was NaH₂PO₄:Na₂CO₃ with 2 × 10^?3:1 × 10^?3 molar ratio and the amount of effervesce powder was 0.4 g. Under optimum conditions enhancement factor, limit of detection and limit of quantification were calculated as 78, 2.9 and 9.7 μg L^?1, respectively. In addition, to prove precision of the method intra-day relative standard deviations were calculated for 10 and 50 μg L^?1 Cu²⁺ concentrations and found as 2.1% and 1.3%, respectively. The proposed method showed good linearity within the range of 10.0–100 μg L^?1. Finally, proposed method was successfully applied to determination of copper traces in aqueous samples.     

Validated HPTLC and HPLC methods for determination of fluorometholone and sodium cromoglycate in presence of their impurities and degradation products; application to kinetic study and on rabbit aqueous humor

Fluorometholone (FLM) and Sodium Cromoglycate (CMG) are co-formulated in ophthalmic preparation and showed marked instability under different conditions. Two specific, sensitive and precise stability-indicating chromatographic methods have been developed and validated for their determination in the presence of their degradation products and FLM impurity. Ten components were efficiently separated by them. The first method was HPTLC-spectrodensitometry, where the separation was achieved using silica gel 60?F₂₅₄ HPTLC plates and developing system of ethyl acetate: methanol (9:1, v/v). The second method was a reversed phase HPLC associated with kinetic study of the degradation process and was successfully applied for determination of the studied compounds in spiked rabbit aqueous humor. The mobile phase was acetonitrile: methanol: 0.05?M potassium dihydrogenphosphate (0.1% trimethylamine); pH 2.5, adjusted with orthophosphoric acid (20: 30: 50, by volume). In both methods, the separated components were detected at 240?nm and system suitability was checked. Good correlation was obtained in the range of 0.10–24.00 and 0.20–48.00?µg band^?1, for FLM and CMG by HPTLC. While for HPLC, the linearity ranges from 0.01–50.00 and 0.05–50.00?µg?mL^?1 for both drugs. The methods were applied in pharmaceutical formulation, where they were compared to the reported method with no significant difference.     

(Vapor + liquid) equilibrium data for (carbon dioxide + 1,1-difluoroethane) system at temperatures from (258 to 343) K and pressures up to about 8 MPa

Accurate thermo-physical data are of utmost interest for the development of new efficient refrigeration systems. Carbon dioxide (R744) and 1,1-difluoroethane (R152a) are addressed here. Isothermal (vapor + liquid) equilibrium data are reported herein for (R744 + R152a) binary system in the (258–343) K temperature range and in the (0.14 to 7.65) MPa pressure range. A reliable “static-analytic” method taking advantage of two online ROLSI? micro capillary samplers is used for all thermodynamic measurements. The data are correlated using our in-house ThermoSoft thermodynamic model using the Peng–Robinson equation of state, the Mathias–Copeman alpha function, the Wong–Sandler mixing rules, and the NRTL model.     

Sensitive Electrochemical Quantification of Proanthocyanidins in Grapevine (Vitis vinifera) by Utilizing Disposable Screen-printed Carbon Electrodes

This work presents quantification of proanthocyanidins (PAs) isolated from grapevine using disposable screen-printed carbon electrodes (SPCE). Procyanidin B2 (B2) used as a model to investigate the electrochemical characteristics of complicated PAs structures in Britton Robinson buffer solution using cyclic voltammetry and square wave voltammetry. B2 exhibits a well-defined reversible redox wave at +0.49 V vs. Ag/AgCl. Significantly, the B2 was determined over a linear concentration range of 3.45–34.6 μM with a detection limit of 2.07 μM. The SPCE was used to analyze PAs in grapevine samples, and the results were consistent with those obtained using Folin-Ciocalteu standard method.     

Physical immobilization of Rhizopus oryzae lipase onto cellulose substrate: activity and stability studies

Rhizopus oryzae lipase (ROL) was immobilized by adsorption onto oxidized cellulose fibers and regenerated films. The maximum adsorption level increases with the raise in the amount of carboxylic groups on cellulose surface confirming that adsorption is being governed mainly by electrostatic interaction between the enzyme and the substrate. This hypothesis was further confirmed by zeta-potential measurements showing a decrease in the zeta-potential of the fibers after enzyme adsorption. XPS analysis showed an intensification of the N 1s peak attesting the presence of the enzyme on the surface. The effect of temperature, pH and solvent polarity on the immobilized enzyme activity and stability was investigated. The catalytic esterification of oleic acid with n-butanol has been carried on using hexane as an organic solvent. A high conversion yield was obtained (about 80%) at 37 degrees C with a molar ratio of oleic acid to butanol 1:1 and 150IU immobilized lipase. The adsorption achieved two successive cycles with the same efficiency, and started to lose its activity during the third cycle.     

Spectroscopy analyses of hybrid unsaturated polyester composite reinforced by Alfa,wool, and thermo-binder fibres

Alfa’s fibres surfaces were modified chemically by the presence of wool and [poly(ester terephthalate) (PET)–polyethylene (PE)] thermo-binder fibres. Indeed, vibrational analyses based on Fourier transform infrared spectroscopy and Raman measurements have confirmed the existence of chemical interactions between these fibres. These analyses have shown that the hydrophilic character of Alfa fibres could be decreased either by hydrogen bonds between water molecules and wool fibres or by the crystallinity of PET constituents in PET-PE thermo-binder fibres which might confer its hydrophobic character to Alfa’s fibres surfaces. As a result, the compatibility between the Alfa fibres and the unsaturated polyester matrix was enhanced, which allowed adhesion mechanism based on chemical bonds formed by secondary bonding. Such adhesion mechanism was also proven by the ¹³C Cross-Polarization Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy results.     

Enantioanalysis of bisoprolol in human plasma with a macrocyclic antibiotic HPLC chiral column using fluorescence detection and solid phase extraction

A sensitive, enantioselective, high-performance liquid chromatographic (HPLC) method was developed and validated to determine S-(-)- and R-(+)-bisoprolol in human plasma. Baseline resolution was achieved using the teicoplanin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic T with a polar ionic mobile phase (PIM) consisting of methanol-glacial acetic acid-triethylamine (100 : 0.02 : 0.025, v/v/v) at a flow rate of 1.5 ml/min and fluorescence detection set at 275 nm for excitation and 305 nm for emission. All analyses with S-(-)-atenolol as the internal standard were conducted at ambient temperature. The assay involved the use of a solid-phase extraction procedure for human plasma samples prior to HPLC analysis. The C18 cartridge gave good recovery rates for both enantiomers without any interference. The method was validated over the range of 20-200 ng/ml for each enantiomer concentration. Recovery rates for S-(-)- and R-(+)-bisoprolol enantiomers were in the range of 95-102%. The method proved to be precise (within-run precision expressed as % RSD ranged from 1.0-6.2% and between-run precision ranged from 0.9-6.7%) and accurate (within-run accuracies expressed as percentage error ranged from 0.2-4.8% and between-run accuracies ranged from 0.3-1.7%). The limit of quantitation and limit of detection for each enantiomer in human plasma were 20 and 5 ng/ml, respectively.     

Mechanism and kinetics of glass-ceramics formation in the LiO2-SiO2-CaO-P2O5-CaF2 system

Two glasses based on lithium disilicate (LS₂), with and without fluorapatite (FA), were synthesised in the Li₂O-SiO₂-CaO-P₂O₅-CaF₂ system with P₂O₅: CaO: CaF₂ ratios corresponding to fluorapatite. Glass-ceramics have then been prepared by thermal treatment. The mechanism and kinetics of crystallization as functions of grain size and rate of heating were investigated using thermal analysis methods. The smaller particles crystallize preferentially by surface crystallization, which is replaced by volume crystallization at larger particle sizes. Inclusion of FA in the LS₂ favours crystallization through the surface mechanism. The onset limit for volume crystallization replacing the surface mechanism is at about 0.3 mm for pure LS₂ glass and 0.9 mm for glass containing FA. The calculated activation energies of the glasses (₂99 ± 1 kJ mol-1 for pure LS₂ glass and ₂88 ± 7 kJ mol⁻¹ for glass containing FA according to Kissinger, or 313 ± 1 kJ mol-1 for pure LS₂ glass and 303 ± 8 kJ mol-1 for glass containing FA according to Ozawa) indicate that the tendency of the glasses to crystallize is supported by the FA presence. Bioactivity of all samples has been proved in vitro by the formation of new layers of apatite-like phases after soaking in SBF.      

Intersubband transitions in In_xAl_(1-x)N/In_yGa_(1-y)N quantum well operating at 1.55 μm

In this paper, we theoretically study the effects of doping concentration NDand an external electric field on the intersubband transitions in InxAl(1-x)N/InyGa(1-y)N single quantum well by solving the Schr¨odinger and Poisson equations self-consistently. Obtained results including transition energies, the band structure, and the optical absorption have been discussed. The lowest three intersubband transitions(E2- E1),(E3- E1), and(E3- E2) are calculated as functions of doping concentration ND. By increasing the doping concentration ND, the depletion effect can be reduced, and the ionized electrons will compensate the internal electric field which results from the spontaneous polarization. Our results show that an optimum concentration NDexists for which the transition 0.8 eV(1.55 μm) is carried out. Finally, the dependence of the optical absorption α13(ω) on the external electric field and doping concentration is studied. The maximum of the optical absorption can be red-shifted or blue-shifted through varying the doping concentration and the external electric field. The obtained results can be used for designing optical fiber telecommunications operating at 1.55 μm.     

Intersubband transitions in InxAl（l-x）N/InyGa（l-y）N quantum well operating at 1.55 μm

In this paper, we theoretically study the effects of doping concentration ND and an external electric field on the intersubband transitions in InxAl（l-x）N/InyGa（l-y）N single quantum well by solving the Schrodinger and Poisson equations self-consistently. Obtained results including transition energies, the band structure, and the optical absorption have been discussed. The lowest three intersubband transitions （E2 -El）, （E3 -El）, and （E3 -E2） are calculated as functions of doping concentration ND. By increasing the doping concentration ND, the depletion effect can be reduced, and the ionized electrons will compensate the internal electric field which results from the spontaneous polarization. Our results show that an optimum concentration ND exists for which the transition 0.8 eV （1.55 μm） is carried out. Finally, the dependence of the optical absorption α13（ω） on the external electric field and doping concentration is studied. The maximum of the optical absorption can be red-shifted or blue-shifted through varying the doping concentration and the external electric field. The obtained results can be used for designing optical fiber telecommunications operating at 1.55 μm.