Determination of migrated phthalic acid residues into edible oils using a green mode of air-assisted liquid–liquid microextraction followed by high-performance liquid chromatography–diode array detector

In this study, for the first time, an organic solvent-free air-assisted liquid–liquid microextraction method has been reported for the extraction and preconcentration of phthalic acids (o-phthalic acid, m-phthalic acid, and p-phthalic acid) from edible oil samples. The method is based on the repeated aspirating/injection of an alkaline aqueous solution and the oil sample mixture in a conical bottom centrifuge tube to form a cloudy solution. After phase separation by centrifuging, the sedimented phase is directly analyzed by high-performance liquid chromatography–diode array detection. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.11–0.29 and 0.28–0.91 ng mL^?1, respectively. Extraction recoveries and enrichment factors were from 81 to 97% and 406 to 489, respectively. The relative standard deviations for the analysis of 5 ng mL^?1 of each analyte were less than 5.9% for intraday (n = 6) and interday (n = 5) precisions. Finally, different oil samples were successfully analyzed using the proposed method and m-phthalic acid, and p-phthalic acid were determined in some of them at ng mL^?1 level.     

Similarities and Differences of Low Salinity Polymer and Low Salinity LPS (Linked Polymer Solutions) for Enhanced Oil Recovery

Linked polymer solution (LPS) is nano-size particles made of hydrolyzed polyacrylamide (HPAM) cross-linked with aluminum citrate. The propagation of LPS has been compared to non-cross-linked polymers at low brine salinity condition. The possible differences in properties and potentials for oil recovery have been investigated using water-wet and intermediate-wet cores. The target oil for polymer flooding (PF) is assumed to be the portion of the reservoir that has been bypassed by water during waterflooding and not the residual oil saturation in flooded zones. Our recent studies have shown that a positive synergy can be obtained by combining low salinity and PF. It has been claimed in the literature that cross-linking polymer such as colloidal dispersion gels (colloidal dispersion gels (CDG), micron-size aggregates) or LPS (nano-size particles) would extend the application of polymers to also include change in residual oil saturation. The results of this study indicated higher pressure buildup when low salinity LPS was propagated through brine saturated cores compared to low salinity polymer solution. The pressure buildup was even stronger for high salinity LPS injection. In two phase flow experiments, both polymer and LPS under low salinity condition, showed approximately similar propagation and oil recovery potential when injected into water-wet and intermediate-wet cores.     

Development of Nonenzymatic Hydrogen Peroxide Sensor Based on Successive Pd‐Ag Electrodeposited Nanoparticles on Glassy Carbon Electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed by electrodepositing palladium? silver nanoparticles (NPs) on a glassy carbon electrode. The morphology of the modified electrode was characterized by Scanning electron microscopy (SEM). The result of electrochemical experiments showed that such constructed sensor had a favorable catalytic ability, high sensitivity, excellent selectivity towards reduction of hydrogen peroxide (H₂O₂). The response to H₂O₂ is linear in the range between 0.30 μM to 2.50 mM, and the detection limit is 0.1 μM (at an S/N of 3).     

Star complements in regular graphs: Old and new results

We survey results concerning star complements in finite regular graphs, and note the connection with designs and strongly regular graphs in certain cases. We include improved proofs along with new results on stars and windmills as star complements.     

Ultrasound-assisted temperature-controlled ionic-liquid dispersive liquid-phase microextraction method for simultaneous determination of anethole,estragole, and para-anisaldehyde in different plant extracts and human urine: a comparative study

In this study, the performances of four ionic-liquid-based microextraction methods, ionic-liquid-based dispersive liquid–liquid microextraction (IL-DLLME), ionic-liquid-based ultrasound-assisted emulsification microextraction (IL-USA-ME), temperature-controlled ionic-liquid dispersive liquid-phase microextraction (TC-IL-DLME), and ultrasound-assisted temperature-controlled ionic-liquid dispersive liquid-phase microextraction (USA-TC-IL-DLME), were investigated for extraction of three bioactive compounds (anethole, estragole, and anisaldehyde) from different plant extracts and human urine. Anethole and estragole were chosen because they can alter cellular processes positively or negatively, and an efficient method is needed for their extraction and sensitive determination in the samples mentioned. Because there is no previous report on the separation of anethole and estragole (structural isomers), first, simultaneous gradient elution and flow programming were used. The microextraction methods were then applied and compared for analysis of these compounds in plant extracts and human urine by use of high-performance liquid chromatography (HPLC). The effect of conditions on extraction efficiency was studied and under the optimum conditions, the best enrichment factors (58–64), limits of detection (14–18 ng mL^?1), limits of quantification (47–60 ng mL^?1), and recovery (94.4–101.7 %) were obtained by use of USA-TC-IL-DLME. The optimized conditions were used to determine anethole, estragole, and para-anisaldehyde in fennel, anise, and tarragon extracts and in human urine.     

Simultaneous determination of valproic acid and its main metabolite in human plasma using a small scale dispersive liquid–liquid microextraction followed by gas chromatography–flame ionization detection

A simple, sensitive, and rapid analytical method has been developed and validated for the extraction and quantification of valproic acid and its main metabolite (3-heptanone) in human plasma. Initially, the proteins of plasma were precipitated with trifluoroacetic acid. Then a very small volume of a water-immiscible extractant and acetonitrile was mixed and rapidly injected into the pre-treated plasma sample. For further turbidity (dispersion of the extractant into sample solution), the cloudy solution was vortexed. After centrifugation, the settled phase was injected into gas chromatography-flame ionization detection. The effective parameters, such as type and volume of extraction and disperser solvents, vortex time, and pH were studied and optimized. The limits of detection of valproic acid and 3-heptanone were obtained, 0.065 and 0.015 mg L^?1, respectively. An acceptable precision was obtained for a concentration of 2 mg L^?1 of each analyte (relative standard deviation?≤?8%). The average absolute recoveries (n?=?3) of valproic acid and 3-heptanone were 52?±?2 and 42?±?1%, respectively. The validated method has been successfully used in analysis of the analytes in human plasma samples.     

Amperometric NADH sensor based on a carbon ceramic electrode modified with the natural carotenoid crocin and multi-walled carbon nanotubes

A carbon ceramic electrode (CCE) was fabricated from a composite consisting of sol-gel, ceramic graphite, multi-walled carbon nanotubes and the natural carotenoid crocin. The resulting sensor is shown to allow for the determination of NADH at a rather low working potential of 0.22 V (vs. Ag/AgCl). The heterogeneous electron transfer rate constant (k_s) and the surface coverage of the modified electrode are 16.8 s^?1 and 22 pmol·cm^?2, respectively. The sensor shows excellent and linear response in solutions of pH 7.0 over the 0.5 to 100 μM NADH concentration range, a 0.1 μM detection limit, and a sensitivity of 251.3 nA·μM^?1·cm^?2.

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Graphical abstract Schematic of the preparation of a carbon ceramic electrode modified with electropolymerized crocin on multi-walled carbon nanotubes. This sensor has a strongly decreased oxidation overpotential for NADH.

     

Interval Minors of Complete Bipartite Graphs

Interval minors of bipartite graphs were recently introduced by Jacob Fox in the study of Stanley–Wilf limits. We investigate the maximum number of edges in ‐interval minor‐free bipartite graphs. We determine exact values when and describe the extremal graphs. For , lower and upper bounds are given and the structure of ‐interval minor‐free graphs is studied.