A new solid phase micro extraction for simultaneous head space extraction of ultra traces of polar and non-polar compounds

The results of the innovative study on a new stationary phase with high efficiency based on ZnO nano and micro rod coating on fused silica are reported in this paper. ZnO nanorods with a diameter in the range of 70–300 nm and the length of about 500 nm, have been grown on fused silica fibers using a hydrothermal process. The extraction properties of the fiber were investigated using headspace solid-phase microextraction (HS-SPME) mode coupled with gas chromatography–mass spectrometry detection (GC–MS) for 1,4-dichloro-nitrobenzene, biphenyl and acenaphthene. The calibration curves were linear up to 10²–10⁷ ng L⁻¹ (R² > 0.995) with detection limits of 10⁻³ ng L⁻¹ for biphenyl and acenaphthene and 10 ng L⁻¹ for 1,4-dichloro-nitrobenzene. The RSD for single fiber and fiber-to-fiber were less than 7.0 and 11.5%, respectively. The high stability of the ZnO coating is proved at relatively high temperatures (up to 300 °C) with a high extraction capacity and long lifespan (more than 100 times). Promising recoveries (91–102%) were obtained in environmental water samples analysis by applying the proposed technique.     

The Reaction of (N‐Isocyanimino)triphenylphosphorane with Biacetyl in the Presence of Aromatic Carboxylic Acids: Efficient One‐Pot Three‐Component Reaction for the Synthesis of 3‐(5‐Aryl‐1,3,4‐oxadiazol‐2‐yl)‐3‐hydroxybutan‐2‐one Derivatives

Reactions of biacetyl (=butane‐2,3‐dione) with (N‐isocyanimino)triphenylphosphorane in the presence of aromatic carboxylic acids proceed smoothly at room temperature and under neutral conditions to afford 3‐(5‐aryl‐1,3,4‐oxadiazol‐2‐yl)‐3‐hydroxybutan‐2‐one derivatives in high yields.     

Residual and Past Discrete Tsallis and Renyi Extropy with an Application to Softmax Function

In this paper, based on the discrete lifetime distribution, the residual and past of the Tsallis and Renyi extropy are introduced as new measures of information. Moreover, some of their properties and their relation to other measures are discussed. Furthermore, an example of a uniform distribution of the obtained models is given. Moreover, the softmax function can be used as a discrete probability distribution function with a unity sum. Thus, applying those measures to the softmax function for simulated and real data is demonstrated. Besides, for real data, the softmax data are fit to a convenient ARIMA model.     

Electrochemical determination of naproxen in the presence of acetaminophen using a carbon paste electrode modified with activated carbon nanoparticles

In this study, cyclic voltammetry and differential pulse voltammetry were used to determine the electrochemical properties and concentration of naproxen in pharmaceutical formulation and human serum samples by using a carbon paste electrode modified with activated carbon nanoparticles. Optimum conditions were obtained at an electrode with 0.005 g activated carbon nanoparticles in a phosphate buffer solution of pH 6 as a supporting electrolyte. Linear calibration curves were obtained in the range of 0.1–120 μM, and the detection limit of naproxen determined was 0.0234 μM. The modified electrode shows good selectivity for naproxen in the presence of some organic and inorganic interferences and very good precision in real samples. Finally, naproxen was measured in the presence of acetaminophen.     

Reproducing-kernel-based splines for the regularization of the inverse ellipsoidal gravimetric problem

To solve the inverse gravimetric problem, i.e. to reconstruct the Earth's mass density distribution by using the gravitational potential, we introduce a spline interpolation method for the ellipsoidal Earth model, where the ellipsoid has a rotational symmetry. This problem is ill-posed in the sense of Hadamard as the solution may not exist, it is not unique and it is not stable. Since the anharmonic part (orthogonal complement) of the density function produces a zero potential, we restrict our attention only to reconstruct the harmonic part of the density function by using the gravitational potential. This spline interpolation method gives the existence and uniqueness of the unknown solution. Moreover, this method represents a regularization, i.e. every spline continuously depends on the given gravitational potential. These splines are also combined with a multiresolution concept, i.e. we get closer and closer to the unknown solution by increasing the scale and adding more and more data at each step.     

Synthesis of a new Pt(II) complex containing valganciclovir drug and calf-thymus DNA interaction study using multispectroscopic methods

A new complex, [Pt(valcyte)(DMSO)Cl]Cl, in which valcyte (trade name) served as valganciclovir hydrochloride drug ([2-[(2-amino-6-oxo-3H-purin-9-yl)methoxy]-3-hydroxypropyl](2S)-2-amino-3-methylbutanoate), was synthesized and characterized by different physicochemical methods. Binding interaction of this complex with calf-thymus DNA (ct-DNA) has been investigated by multispectroscopic techniques. The complex displays significant binding properties with ct-DNA. The results of fluorescence and UV–vis absorption spectroscopy indicated that this complex interacted with ct-DNA in a groove-binding mode, and the binding constant was 3.8 × 10⁴ M^?1. Furthermore, the complex induced detectable changes in the CD spectrum of ct-DNA and slightly changed its viscosity which verified the groove-binding mode. Finally, all results indicated that Pt(II) complex interact with DNA via groove-binding mode.     

Magnetic Field-Assisted Direct Immersion SPME of Endogenous Aldehydes in Human Urine

Direct immersion solid-phase microextraction (DI-SPME) is an effective microsampling strategy for polar and ionic species in aqueous media. Nevertheless, the fiber coating is in direct contact with sample solution and affected by its conditions. To compensate this limitation and to improve the extraction efficiency, a magnetic fiber coating was prepared and employed for DI-SPME sampling under the enhancing effect of a magnetic field. Magnetic iron oxide core–shell silica nanoparticles were synthesized and embedded in polypyrrole using an in situ electropolymerization method along with simultaneous coating on the surface of a platinized stainless-steel fiber. It was then applied for magnetic-assisted DI-SPME (MA-DI-SPME) sampling of endogenous aldehydes in human urine. Sample solution pH, the magnetic field intensity, ionic strength and extraction time were evaluated as the important affecting variables. Limits of detection were obtained 0.01–0.1 ng mL^?1; the calibration graphs were linear over the range of 0.1–10000 ng mL^?1. The inter-fiber (fiber-to-fiber) reproducibility was found to be 10.7–12.5%. Matrix effect from urine samples was not observed at concentration levels of 0.2, 2, and 8 µg mL^?1. The results showed that magnetic field increased the efficiency of DI-SPME method about two to four times. The developed strategy was successfully applied for the extraction and quantification of hexanal and heptanal (as the most important aldehyde biomarkers) in urine samples.

Graphical Abstract

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Evaluation of polypyrrole/silver/polyethylene glycol nanocomposite sorbent for electroenhanced direct-immersion solid-phase microextraction of carvacrol and thymol from medicinal plants

The unique features of nanostructured polypyrrole, conductivity enhancement effect of silver nanoparticles and high polar adsorptivity of polyethylene glycol were merged into polypyrrole/silver/polyethylene glycol (PPy/Ag/PEG) nanocomposite. It was synthesized and simultaneously coated on the surface of a stainless-steel fiber using an amended electropolymerization procedure. Before coating, the fiber substrate was made porous and sticky by allocating platinum dots on the surface of the stainless-steel fiber using the electrophoretic method. The prepared fiber was applied for the extraction of carvacrol and thymol (the most important antioxidants in medicinal plants) through an electroenhanced direct-immersion solid-phase microextraction (EE-DI-SPME) sampling strategy, followed by GC-FID quantification. To achieve the best efficiency, the effectual experimental variables including pH of sample solution, applied voltage, extraction temperature and time, stirring rate, and ionic strength were investigated. Under the optimal experimental conditions, the calibration curves were linear over the range of 0.5–30 µg mL^?1 for thymol and 0.01–30 µg mL^?1 for carvacrol. The detection limits (3S_b) and relative standard deviation (RSD%, n?=?6) were obtained to be 0.15, 0.003 µg mL^?1 and 10.2, 8.7% for thymol and carvacrol, respectively. The results demonstrated the priority of the proposed fiber compared with polypyrrole and polyacrylate fibers, in terms of extraction efficiency, durability and stability. The developed method was successfully employed for the analysis of thymol and carvacrol in medicinal plants.     

Simultaneous voltammetric sensing of acetaminophen,epinephrine and melatonin using a carbon paste electrode modified with zinc ferrite nanoparticles

A highly selective electrochemical sensor was fabricated based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe₂O₄ NPs). The nanocomposite has attractive properties such as high surface-to-volume ratio and good electrocatalytic activity towards the drugs acetaminophen (AC), epinephrine (EP), and melatonin (MT), best at working voltages of 0.35, 0.09 and 0.55 V (vs. Ag/AgCl), respectively. The linear ranges (and detection limits) are 6.5–135 (0.4) μmol L^?1 for AC, 5–100 (0.7) μmol L^?1 for EP, and 6.5–145 (3) μmol L^?1 for MT.

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Graphical abstract A novel electrochemical sensor based on a modified carbon paste electrode with zinc ferrite nanoparticles (ZnFe₂O₄) for the simultaneous detection of the acetaminophen, epinephrine and melatonin was fabricated

     

The Padé-Rayleigh-Ritz method for solving large hermitian eigenproblems

We make use of the Padé approximants and the Krylov sequencex, Ax,,...,A ^m–1 x in the projection methods to compute a few Ritz values of a large hermitian matrixA of ordern. This process consists in approaching the poles ofR _x()=((I–A)^–1 x,x), the mean value of the resolvant ofA, by those of [m–1/m]_Rx(), where [m–1/m]_Rx() is the Padé approximant of orderm of the functionR _x(). This is equivalent to approaching some eigenvalues ofA by the roots of the polynomial of degreem of the denominator of [m–1/m]_Rx(). This projection method, called the Padé-Rayleigh-Ritz (PRR) method, provides a simple way to determine the minimum polynomial ofx in the Krylov subspace methods for the symmetrical case. The numerical stability of the PRR method can be ensured if the projection subspacem is sufficiently small. The mainly expensive portion of this method is its projection phase, which is composed of the matrix-vector multiplications and, consequently, is well suited for parallel computing. This is also true when the matrices are sparse, as recently demonstrated, especially on massively parallel machines. This paper points out a relationship between the PRR and Lanczos methods and presents a theoretical comparison between them with regard to stability and parallelism. We then try to justify the use of this method under some assumptions.