Enzymatic determination of vitamin A in pharmaceutical formulations with spectrophotometric detection

An enzymatic method for the determination vitamin A (retinol) is reported using soluble and immobilized alcohol dehydrogenase, isolated from rabbit liver. The reaction is based on the oxidation of retinol and simultaneous reduction of NAD⁺ to NADH followed by spectrophotometric detection at 340 nm. The calibration graph was linear over the range of 2.0–10 μM with correlation coefficients of 0.9967 and 0.9992 (n = 5) for soluble and immobilized alcohol dehydrogenase respectively, with relative standard deviations (n = 3) in the range of 0.5–1.2%. The limit of detection was lower than 1.0 μM. The proposed method was applied to determine vitamin A in pharmaceuticals, and the results obtained were in reasonable agreement with the amount labeled. The results were compared using spectrophotometric reference method, and no significant difference was found between the results of the both methods.     

On the role of substituent in noncovalent functionalization of graphene and organophosphor recognition: IQA and SAPT perspective

Despite importance of integrating organic molecules with graphene to fabricate graphene‐based electronic devices, the role of substituents and interface stabilizing forces are poorly understood. In this work, the interactions of 7,7,8,8‐tetracyanoquinodimethane (TCNQ), 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), hydroquinone (Q), and tetrafluorohydroquinone (TFQ) with graphene have been investigated by means of interacting quantum atoms and SAPT(DFT). In addition, in context of potential design of a graphene‐based sensor for detection of the nerve agent sarin, we studied the interaction of graphene and the organic molecules with the dimethyl methylphosphonate (DMMP)—the molecule that mimics sarin. The results show that the organic molecules attach to graphene via C(sp²)?C(sp²), C(sp²)?C(sp) and H?π bonds. In addition, they trap DMMP via various linkages such as hydrogen, lonepair?π and H?π . The quantum effects play a significant role. The Pauli repulsion is responsible for p‐doping of graphene. The substituents are stabilized on graphene by the exchange‐correlation energy. The fluorination of the benzenoid ring raises the electron‐sharing . The through space and through bond effects of the fluorine atoms (‐F) increase the classical attraction of the cyano groups and benzenoid ring with graphene, respectively. When comparing performance of the ab initio and DFT methods, MP2 predicts too much attraction due to well‐known overestimation of the dispersion energy by the uncoupled dispersion component for benzene rings, while ω B97xD functional and SAPT(DFT) provide weaker interaction energies, in good agreement with each other.     

Air-assisted in situ deep eutectic solvent decomposition followed by the solidification of floating organic droplets-liquid-liquid microextraction method for extraction of azole antifungal drugs in biological samples prior to high-performance liquid chromatography

A free dispersive method, air-assisted in situ deep eutectic solvent decomposition followed by the solidification of floating organic droplets liquid-liquid microextraction was indicated in this study. This technique was utilized to simultaneously ascertain some azole antifungal drugs prior to high-performance liquid chromatography. In this research, a quasi-hydrophobic deep eutectic solvent was formed from tetrabutylammonium bromide and 1-dodecanol as an organic solvent at a 1:2 molar ratio. The synthesized deep decomposition in the sample solution caused in situ dispersion of extraction solvent and analytes. Air-assisted enhanced a dispersion condition in the sample solution. 1-Dodecanol as a green option was replaced with typical extraction solvents providing the advantages of a suitable freezing point near room temperature and low density. The effect of important analytical parameters on the extraction recovery of analytes was assessed. Under these optimal conditions, the limits of detection and the limits of quantitation determined were in the range of 0.5–2.8 and 1.5–9 μg/L, for water, urine and plasma samples, respectively. The intra-day and inter-day relative standard deviations (n = 5) were calculated to be 2.9–4.6 and 4.2–8.9%, respectively. The results represented the effectiveness of the developed method for the extraction and determination of analytes in biological samples.     

Rapid chemical synthesis of four ferrate(VI) compounds

The preparation of four novel Fe(VI) salts, including PbFeO₄, ZnFeO₄, CdFeO₄ and HgFeO₄ is demonstrated. These Fe(VI) salts were synthesized from a solid phase reaction merely by grinding K₂FeO₄ with M (C₂H₃O₂)₂.nH₂O (M = Pb²⁺, Zn²⁺) or M (NO₃)₂.nH₂O (M = Cd²⁺, Hg²⁺) at room temperature. A rapid and efficient reaction occurred upon grinding the solid reactants to afford high yield ferrate(VI) salts which were characterized by XRD, EDS and FTIR techniques. All of the synthesized ferrates were rather stable and could be stored at room temperature for more than a month with no significant decomposition.     

Sub-Second Accumulation and Stripping for Pico-Level Monitoring of Amikacin Sulphate by Fast Fourier Transform Cyclic Voltammetry at a Gold Microelectrode in Flow-Injection Systems

A novel chemiluminogenic reagent, refered to as spiro form fluorescein hydrazide, was synthesized, and its application to chemiluminescence (CL) determination of Co²⁺ is described. The method is based on the catalytic effect of Co²⁺ on the autoxidation of sulfite in basic solution to generate a series of powerful oxidative intermediates, which then oxidize colorless, nonfluoresent fluorescein hydrazide to generate strong CL emission. The CL signal is linearly related to the concentration of Co²⁺ in the range of 0.1–200nM with a detection limit of 0.04nM. The optimal conditions for the detection of Co²⁺ were evaluated, and the possible CL mechanism is discussed. The proposed method has been applied to the determination of Co²⁺ in pharmaceutical preparations and in soil samples.     

Flow-injection method for the determination of serine using immobilized enzyme

A flow-injection method for the determination of serine using a mini-column containing immobilized serine dehydratase isolated and purified from rat liver is described. Ammonia produced from the enzymatic reaction is coupled with hypochlorite and phenol in an alkaline medium yields a blue product due to the indophenol anion formation, which is the basis of a spectrophotometric detection at 640 nm. The limit of detection (2×blank noise) is 0.01 mM with a sample throughput of 25 h⁻¹. Calibration graph is linear in the range 0.2–1.0 mM, with relative standard deviation 0.6–1.0%.     

RKM for solving Bratu‐type differential equations of fractional order

The purpose of the present paper is to propose an efficient numerical method for solving the differential equations of Bratu‐type with fractional order in reproducing kernel Hilbert space. The exact solution is calculated in the form of a convergent series with easily computable components. Finally, some examples are given to illustrate the efficiency and applicability of the method. Copyright © 2015 John Wiley & Sons, Ltd.     

Nanogram detection of m-dinitroaromatics and their derivatives A re-evaluation of the spot-test based on the janovsky reaction

The spot-test for m-dinitroaromatics and their derivatives, based on the Janovsky reaction, is re-investigated. The sensitivity of the spot-test has been much enhanced by changing the solvent and using the novel “pellet” spot-test. With the “pellet” spot-test and dimethylsulphoxide, 4–50 ng of m-dinitroaromatic compounds and their derivatives can be detected. The change from acetone (used in the original spot-test) to dimethylsulphoxide changes the reaction product in most cases.     

Bioluminescent assays with immobilized firefly luciferase based on flow injection analysis

A flow-injection manifold incorporating immobilized firefly luciferase is described. The detector design and reaction conditions are discussed and results are presented for the determination of adenosine-5′-triphosphate over the range 1 × 10^?12?1 × 10^?5 M. Modifications for creatine phoshokinase (10–400 U l^?1) and creatine phosphate (10^?t–10^?1 M), both determined indirectly via ATP, are also described.