Ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction for the determination of cadmium in water samples: Optimization using response surface methodology

A sensitive, simple, and rapid method is developed for ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction (IPSA-DLLME) and flame atomic absorption spectrometric determination of cadmium in water samples. In this procedure, trace amounts of Cd²⁺ were converted to CdI ₄ ^2– , and after addition of a tetrabutylammonium bromide (TBAB) solution as cationic surfactant the analyte was transformed to the ion-pair state. This cadmium species was extracted by fast injection of a solution containing 200 μL of chloroform and 800 μL of methanol as extraction and disperser solvents, respectively. The pH of the sample solution, concentration of iodide, TBAB amount, and the extractant volume were optimized using a 27-run Box–Behnken design with a triplicate central point. Under the optimized conditions, the calibration curve was linear in the range 1–200 μg L^–1 (R ² = 0.9959); with the detection limit (signal/noise = 3) of 0.28 μg L^–1. The relative standard deviations (RSD) for eight runs (Cd²⁺ = 10 μg L^–1) and enrichment factor were found to be 3.04 % and 50, respectively.     

Identification,control strategies,and analytical approaches for the determination of potential genotoxic impurities in pharmaceuticals: A comprehensive review

Potential genotoxic impurities in pharmaceuticals at trace levels are of increasing concern to both pharmaceutical industries and regulatory agencies due to their possibility for human carcinogenesis. Molecular functional groups that render starting materials and synthetic intermediates as reactive building blocks for small molecules may also be responsible for their genotoxicity. Determination of these genotoxic impurities at trace levels requires highly sensitive and selective analytical methodologies, which poses tremendous challenges on analytical communities in pharmaceutical research and development. Experimental guidance for the analytical determination of some important classes of genotoxic impurities is still unavailable in the literature. Therefore, the present review explores the structural alerts of commonly encountered potential genotoxic impurities, draft guidance of various regulatory authorities in order to control the level of impurities in drug substances and to assess their toxicity. This review also describes the analytical considerations for the determination of potential genotoxic impurities at trace levels and finally few case studies are also discussed for the determination of some important classes of potential genotoxic impurities. It is the authors’ intention to provide a complete strategy that helps analytical scientists for the analysis of such potential genotoxic impurities in pharmaceuticals.     

Novel Bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)Alkanes: Synthesis and Characterization

In this study, 10 different substituted aromatic bis‐benzaldehydes were synthesized by treating hydroxy benzaldehydes with various dihaloalkanes. Bis aldehydes 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j were treated with 2‐(5‐phenyl‐1H‐tetrazole‐1‐yl)acetohydrazide ( 3 ) in acidic medium and in the presence of ammonium acetate to yield a series of new isomeric bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)alkanes ( 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j ) in excellent to good yield. The newly synthesized compounds were characterized by the available spectroscopic analysis.     

1,3-二吗啉基丙烷与Hg(Ⅱ)和Zn(Ⅱ)的配合物:合成、结构与抗菌研究

以1,3-二吗啉基丙烷(DMP)为配体合成了2个配合物:Hg(DMP)Cl₂(1)和Zn(DMP)Cl₂(2),并对其结构进行了表征。单晶X-射线结构分析表明,2个配合物中的金属离子都与2个N原子和2个Cl原子配位,形成扭曲四面体配位结构。配体和配合物对3种革兰氏阳性菌(S. aureus ATCC25923,E. faecalis ATCC23212和S. epidermidis ATCC34384)和3种革兰氏阴性菌(E. coli ATCC25922,P. aeruginosa ATCC27853和K. pneumonia ATCC70063)都具有抗菌活性,且在一定条件下,Hg(Ⅱ)配合物的抗菌活性超过了作为标准的磺胺异恶唑药物。     

Determination of trace amounts of nystatin in water and vaccine samples using sodium dodecyl sulfate-coated iron oxide magnetic nanoparticles followed by high-performance liquid chromatography–ultraviolet detection

In this work, magnetic solid-phase extraction based on sodium dodecyl sulfate-coated Fe₃O₄ nanoparticles has been successfully applied for extraction and preconcentration of trace amounts of nystatin from water and vaccine samples prior to high-performance liquid chromatography–ultraviolet detection. Various experimental parameters affecting extraction and recovery of the analyte, such as the amount of sodium dodecyl sulfate, pH of the sample solution, salt concentration, extraction time, sample volume and desorption conditions, were systematically studied and optimized. Under optimized conditions, nystatin was quantitatively extracted. Proper linear range with good coefficient of determination, (R ² > 0.99) and limit of detection and quantification (based on signal-to-noise ratios of 3 and 10) of 2.0 and 5.0 µg L^?1, over the investigated concentration range (5–700 µg L^?1), were obtained, respectively. The intra-day and inter-day relative standard deviations at 50 µg L^?1 level of NYS were 1.4 and 4.5% based on six replicate determinations. The accuracy of the method was evaluated by recovery measurements on spiked samples. Suitable recoveries of 96–102 and 26–44% were achieved (at spiked levels of 50, 300 and 500 µg L^?1) for water and vaccine samples, respectively.     

Magnetic solid-phase extraction of imatinib and doxorubicin as cytostatic drugs by Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/graphene oxide nanocomposite

Magnetic solid-phase extraction based on Fe₃O₄/graphene oxide nanocomposites was investigated for the separation, preconcentration and determination of imatinib and doxorubicin in aqueous solutions. Synthesis of Fe₃O₄/graphene oxide was characterized by transmission electron microscopy, energy-dispersive X-ray analyzer and vibrating sample magnetometer. After optimizing the conditions, optimal experimental conditions including sample pH, the amount of the magnetic nanoparticles, the effect of salt concentration and other chemotherapy medications, eluent type and extraction time were studied and established. The method showed good linearity for the determination of doxorubicin and imatinib in the concentration range of 0.01–100 μg mL^?1 in aqueous solutions with limit of detection 1.8 ng mL^?1 for doxorubicin and 1.9 ng mL^?1 for imatinib. The relative recoveries of doxorubicin and imatinib levels were 96.7 and 88.4%, respectively. The results indicate that the present procedure is a suitable method for extraction of imatinib and doxorubicin from environmental water samples.     

Approximating the traveling wavefront for a nonlocal delayed reaction-diffusion equation

In this paper a boundary layer method is combined with an asymptotic expansion method to approximate the traveling wave solution of a nonlocal delayed reaction-diffusion model. In particular, assuming that the diffusion coefficients of the mature and immature populations are small, the wave solution is approximated in three steps. First, the model is reduced by considering the Dirac delta function as the kernel function of the integral term. Second, a boundary layer method is employed to approximate the wave solution of the reduced model. Third, using this result and the generalized Watson’s lemma, the wave solution of the general model is approximated. By considering various birth functions, the approximate wave solutions are numerically compared with the exact wave solutions.     

On the transient non-Fickian dispersion theory

The Fickian dispersion equation is the basic relationship used to describe the nonconvective mass flux of a solute in a porous medium. This equation prescribes a linear relationship between the dispersive mass flux and the concentration gradient. An important characteristic of the Fickian relationship is that it is independent of the history of dispersion (e.g. the time rate of change of the dispersion flux). Also, the dispersivities are supposed to be medium constants and invariant with temporal and spatial scales of observation. It is believed that in general these restrictions do not hold. A number of authors have proposed various alternative relationships. For example, differential equations have been employed that prescribe a relationship between the dispersion flux and its time and space derivatives. Also, stochastic theories result in integro-differential equations in which dispersion tensor grow asymptotically with time or distance. In this work, three different approaches, which lead to three different non-Fickian equations with a transient character, are discussed and their primary features and differences are highlighted. It is shown that an effective dispersion tensor defined in the framework of the transient non-Fickian theory, grows asymptotically with time and distance; a result which also follows from stochastic theories. Next, principles of continuum mechanics are employed to provide a solid theoretical basis for the non-Fickian transient dispersion theory. The equation of motion of a solute in a porous medium is used to provide a rigorous derivation of various dispersion relationships valid under different conditions. Under various simplifying assumptions, the generalized theory is found to agree with the conventional Fickian theory as well as several other non-Fickian relationships found in the literature. Moreover, it is shown that for nonconservative solutes, the traditional dispersion tensor is affected by the rate of mass exchange of the solute.Also with National Institute of Public Health and Environmental Protection (RIVM), PO Box 1; 3720BA Bilthoven, The Netherlands     

Substituted six-membered ring carbenes: the effects of amino and cyclopropyl groups through DFT calculations

DFT calculations are employed to compare and contrast six-membered ring carbenes including 1,3-dimethyltetrahydropyrimidin-2-ylidene (1a), 1-methyl-3-cyclopropyltetrahydropyridine-2-ylidene (2a), and 1,3-dicyclopropylcyclohexane-2-ylidene (3a) as well as their unsaturated analogues 1b, 2b, 3b, and 2c. The amino groups exert singlet-triplet energy separation (?E_s−t) of 60.9 kcal/mol to 1a while cyclopropyls induce a ?E_s−t of 14.8 kcal/mol to 3a. The simultaneous presence of amino and cyclopropyl in 2a leads to a ?E_s−t of 43.3 kcal/mol. Unsaturation slightly increases the ?E_s−t of 1a and 3a but not that of 2a. Our thermodynamic, kinetic, and reactivity results are compared with those of synthetic five-membered ring N-heterocyclic carbenes.