A new concept of hollow fiber liquid–liquid–liquid microextraction compatible with gas chromatography based on two immiscible organic solvents

A new concept of liquid–liquid–liquid microextraction (LLLME) was introduced based on applying two immiscible organic solvents in lumen and wall pores of hollow fiber (HF). With this methodology, analytes of interest can be extracted from aqueous sample, into a thin layer of organic solvent (dodecane) sustained in the pores of a porous hollow fiber, and further into a μL volume of organic acceptor (acetonitrile or methanol) located inside the lumen of the hollow fiber. Some chlorophenols (CPs) were selected as model compounds for developing and evaluating of the method performance. The analysis was performed by gas chromatography–electron capture detection (GC–ECD) without derivatization. The factors affecting the HF-LLLME of target compounds were investigated and the optimal extraction conditions were established. Under the optimum conditions, preconcentration factors in a range of 208–895 were obtained. The performance of the proposed method was studied in terms of linear dynamic ranges (LDRs from 0.02 to 100 ng mL⁻¹), linearity (R² ≥ 0.995), precision (RSD % ≤ 8.1) and limits of detection (LODs in the range of 0.006–0.2 ng mL⁻¹). In addition to preconcentration, HF-LLLME also served as a technique for sample clean-up.     

Mechanistic Study of Ozone-Water Reaction and Their Reaction Products with Gas Phase Elemental Mercury:A Computational Study

The interaction of oxygen of water and central oxygen of ozone produces stable H₂O‐O₃ complex with no barrier. With decomposition of this complex through H‐abstraction by O₃ and O‐abstraction by H₂O, four possible product channels have been found. The reaction of mercury and the products of water‐ozone reaction have been studied. All geometrical and AIM parameters of intermediate, transition states, and the products of reactions are calculated and thermodynamic parameters are obtained. The negative value of free energy show that channels Hg+H₂OO, Hg+H₂O₂ and Hg+H₂O₄ in hydrogen tetroxide form (HTO) may be the main reaction channels.     

Antieigenvalue techniques in statistics

In a number of his recent papers Karl Gustafson has outlined the similarities between the Antieigenvalue Theory he founded and several finite dimensional matrix optimization theorems for positive matrices arising in statistics. In this paper, we will show how the techniques that the author and Karl Gustafson have used for computation of Antieigenvalues can also be applied to prove and generalize these matrix optimization theorems in statistics. We will primarily focus on two techniques which we have used in Antieigenvalue computations in recent years. These two techniques are a two nonzero component property for certain class of functionals, and converting the matrix optimization problems in statistics to a convex programing problem. Indeed, these two techniques allow us to generalize some of the matrix optimization problems arising in statistics to strongly accretive operators on finite or infinite dimensional Hilbert spaces.     

Density and viscosity of pyridinium-based ionic liquids and their binary mixtures with water at several temperatures

Densities and viscosities of two pyridinium-based ionic liquids, 1-butylpyridinium tetrafluoroborate [BuPy][BF₄] and 1-octylpyridinium tetrafluoroborate [OcPy][BF₄], and their binaries with water at atmospheric pressure and temperatures from (283.15 to 348.15) K were determined. The densities and viscosities of pure ionic liquids were correlated successfully by empirical equations. The Vogel–Fulcher–Tammann equations can fit the experimental viscosities for pure and binary of both IL systems. Excess molar volume and viscosity deviation were calculated for the binaries. The excess molar volumes have positive deviation from ideal solution while the viscosity deviations have negative values.     

Measurement and correlation of antifungal drugs solubility in pure supercritical CO2 using semiempirical models

In the present study the solubilities of two antifungal drugs of ketoconazole and clotrimazole in supercritical carbon dioxide were measured using a simple static method. The experimental data were measured at (308 to 348) K, over the pressure range of (12.2 to 35.5) MPa. The mole fraction solubilities ranged from 0.2 · 10^?6 to 17.45 · 10^?5. In this study five density based models were used to calculate the solubility of drugs in supercritical carbon dioxide. The density based models are Chrastil, modified Chrastil, Bartle, modified Bartle and Mendez-Santiago and Teja (M–T). Interaction parameters for the studied models were obtained and the percentage of average absolute relative deviation (AARD%) in each calculation was displayed. The correlation results showed good agreement with the experimental data. A comparison among the five models revealed that the Bartle and its modified models gave much better correlations of the solubility data with an average absolute relative deviation (AARD%) ranging from 4.8% to 6.2% and from 4.5% to 6.3% for ketoconazole and clotrimazole, respectively. Using the correlation results, the heat of drug–CO₂ solvation and that of drug vaporization was separately approximated in the range of (?22.1 to ?26.4 and 88.3 to 125.9) kJ · mol^?1.     

Computational study on the reaction mechanism of the gas-phase atom-negative ion of S?+?NO2 ?: comparative study of mechanism with S?+?O3 reaction as isoelectronic and isostructure systems

The reaction mechanism of sulfur vapor (S) with nitrite ion (NO₂ ⁻) has been investigated theoretically on the triplet and singlet potential energy surfaces (PESs). All stationary points for the title reaction have been optimized at the B3LYP/6-311+G(3df) level. The energetic data have been obtained at the CCSD(T)//B3LYP level employing the 6-311+G(3df) basis set. Five stable collision complexes, ³IN1 (S–ONO⁻), ³IN2 (cyclic SONO⁻), ¹IN1 (cis S–ONO⁻), ¹IN2 (S–NO₂ ⁻), and ¹IN3 (trans S–ONO⁻), have been considered on the triplet and singlet PESs through barrier-less and exothermic processes. By starting from these complexes, a simple mechanism has been obtained on the triplet PES while a complex mechanism has been considered on the singlet PES. The calculated results show that there are no favorable paths for the reaction of S with NO₂ ⁻ on the singlet PES. Therefore, the S + NO₂ ⁻ reaction proceeds only on the triplet PES to produce ³SO + ³NO⁻ as main products. The results from the comparative study of S + NO₂ ⁻ reaction mechanism with S + O₃ (as isoelectronic and isostructure reactions) on the singlet PES show similarities in the overall trend of reaction mechanism and atom connectivity and differences in the stability of intermediates and the energy barriers of transition states.     

Extension of elliptic curves on Krasner hyperfields

The aim of the article is to initiate a new study in the framework of algebraic hyperfields, with an applicative impact in cryptography. First we define the notions of generalized Weierstrass equation and elliptic hypercurve on Krasner hyperfields, as a generalization of the notion of elliptic curve on fields. Then we investigate properties of the hypergroups derived from elliptic hypercurves and of the associated H_v-groups. Finally, we present a class of canonical hypergroups, which can be used as an alphabet in a special cryptographic system.