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41.
A new, simple and sensitive method for the spectrophotometric indirect determination of ascorbic acid in fruits, beverages, and pharmaceuticals is described. In this method, the ascorbic acid reduces Cu2+ to Cu+ and reacts with 2,9‐dimethyl‐1,10‐phenanothroline (neucoproine) to form Cu (neucoproine)+ complex, and it was extracted with N‐phenylbenzimidoylthiourea (PBITU) in chloroform. The apparent value of molar absorptivity of the complex in terms of ascorbic acid is (3.52) × 104 L mole?1 cm?1 at λmax, 460. The detection limit of ascorbic acid is 40 μg L?1 and the method obeys Beer's law over the concentration range of 0.1–4.0 μg mL?1. The proposed method was successfully applied for the determination of ascorbic acid in various samples. The validity of the present method was checked by the flow injection analysis (FIA) method. 相似文献
42.
Kamlesh Parwani 《Proceedings of the American Mathematical Society》2005,133(6):1677-1683
Let be a homeomorphism of the torus isotopic to the identity and suppose that there exists a periodic orbit with a non-zero rotation vector . Then has a topologically monotone periodic orbit with the same rotation vector.
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Reaction of 5α‐cholestan‐6‐one oxime ( 1 ), its 3β‐acetoxy and 3β‐chloro analogs, 2 and 3 , respectiveley, with ClCH2CH2NH2?HCl in presence of MeONa afforded 6‐[(2‐aminoethoxy)imino]‐5α‐cholestane ( 4 ), 3β‐acetoxy‐6‐[(2‐aminoethoxy)imino]‐5α‐cholestane ( 5 ), and 6‐[(2‐aminoethoxy)imino]‐3β‐chloro‐5α‐cholestane ( 6 ), respectively. The structures of newly synthesized compounds have been established on the basis of physical, analytical, and spectral data. Theoretical calculations were assessed by using DFT at B3LYP/6‐31G* level to describe the mechanism of the reaction. The stability and feasibility of all the generated structures studied in this report were supported by their respective fundamental frequencies and energy minima. 相似文献
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A simple, rapid and sensitive hollow-fiber with drop-to-drop solvent microextraction (HF-DDSME) combined with gas chromatography?Cmass spectrometry (GC?CMS) has been successfully developed for extraction and determination of antidepressants drugs (AD) in blood sample. The parameters that affect the separation and preconcentration of AD from sample solution were investigated. Calibration curve obtained for three AD were in the range of 100?C1,000; 150?C1,200; and 80?C1,200 ng mL?1 for amitriptyline, imipramine, and promethazine, respectively, with correlation coefficient (R 2 ) between 0.990 and 0.997. The limit of detection (LOD) obtained for amitriptyline, imipramine and promethazine was 25, 30 and 18 ng mL?1, respectively. The developed method has been successfully applied for the determination of AD concentration in blood sample, and the recoveries for the spiked samples were in the range of 92.3?C97.6%. The sample preparation procedure is very simple, effective and virtually solvent-free, and indicated to be a good alternative for the traditional liquid?Cliquid extraction. Finally, the proposed method was successfully applied for the determination of drug concentration of AD in human blood sample. 相似文献
47.
K. K. Upadhyay Shalini Upadhyay Ajit Kumar Kamlesh Thapliyal Santosh K. Srivastava 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1820-1834
Abstract 2-{[4-(Thiazol-2-ylsulfamoyl)-phenyl]-hydrazono}-malonic acid diethyl ester (R1) and 2-{[4-(5-methyl-isoxazol-3-ylsulfamoyl)-phenyl]-hydrazono}-malonic acid diethyl ester (R2) were synthesized through diazocoupling of sulfathiazole and sulfamethoxazole, respectively, with diethyl malonate. They were characterized through various spectroscopic and mass spectral studies. R2 was also characterized through a single crystal X-ray diffraction (XRD) study. Only R1 selectively recognized Hg2+ from a wide range of metal ions through naked-eye change. A color change from orange to olive green was observed upon addition of 1.0 equivalent of Hg2+ as its chloride salt to the 1 × 10?3 M DMSO solution of R1. The role of DMSO in the sensing process appears to be the crucial one, because the solvent-assisted band of R1 at 482 nm observed in its UV-Vis spectrum in DMSO did not appear in its spectra recorded in nujol or in a polar aprotic solvent. The UV-Vis and 1H NMR titrations revealed that the formation of six-membered 1:1 chelate between R1 and Hg2+ triggering the desolvation of R1 as the key step towards its sensing activity. The determination of binding stoichiometry between R1 and Hg2+ along with binding constant has also been discussed. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT 相似文献
48.
Kamlesh Pandey Mrigank Mauli Dwivedi Markandey Singh Nidhi Asthana S. L. Agrawal 《Russian Journal of Electrochemistry》2014,50(2):170-175
In the present work, improvement in ion transport property of polyvinyl formal (PVF)-based nanocomposite polymer electrolytes has been studied upon dispersal of multiwall carbon nanotube (MWCNT) filler. Nanocomposite polymer electrolyte (NCPE) films of xPVF: (1 ? x)CH3COONH4 (ammonium acetate) were prepared by solution cast technique. The formation of nanocomposite has been ascertained by X-ray diffraction (XRD) pattern, which also shows that doping of salt increases amorphousness through polymer salt complexation. Changes in surface morphology have been observed in optical microscopy and Scanning Electron Microscopic (SEM) images. Variation of dielectric constant, dielectric loss, tangent loss and modulus spectra with the change in frequency and temperature were studied with the aid of impedance spectroscopy. 相似文献
49.
Simple, rapid and inexpensive one-step reverse micellar microextraction (RMME) procedures were combined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) for the determination of thiol-containing peptides and amino acids. In this investigation, a thiol-containing peptide (HW6) was chosen as model compound to understand the mechanism of RMME. The electrostatic interactions between the thiol-containing peptide and reverse micelles were proposed to be reason for the transfer of analytes from the aqueous phase to the organic phase. Reverse micelles were formed by the cationic surfactant, methyltrioctylammonium chloride (MTOAC). The best extraction efficiency of HW6 was obtained under the following conditions: pH 11.0, ionic strength 5.0 mM of KCl and micelle concentration 7.0 mM of MTOAC. The limits of detection (LODs) obtained for HW6 in water, urine and plasma samples were 0.15, 0.19 and 0.28 microM, respectively, with relative standard deviation (RSD) values in the range +/-8.8-10.5%. The sensitivity obtained in water by the present method was 45-fold higher than that of the conventional use of atmospheric-pressure (AP)-MALDI MS. Furthermore, the applicability of the proposed approach was extended for the determination of thiol-containing amino acids in sample solutions by using MALDI time-of-flight (TOF) MS. 相似文献
50.
A strategy is presented for the analysis of sulfur drugs and biothiols using silver nanoparticles (AgNPs) capped with different functional groups as the matrix and affinity probes in surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) and atmospheric pressure-matrix assisted laser desorption/ionization ion trap mass spectrometry (AP-MALDI-ITMS). Biothiols adsorbed on the surface of AgNPs through covalent bonding were subjected to ultraviolet (UV) radiation that enabled desorption and ionization due to the excellent photochemical property of NPs. The proposed method has been successfully applied for the determination of cysteine and homocysteine in human urine samples using an internal standard. The limit of detection (LOD) and limit of quantification (LOQ) for cysteine and homocysteine in urine sample are 7 and 22 nM, respectively, with a relative standard deviation (RSD) of <10%. The advantages of the present method compared with the methods reported in the literature for biothiol analysis are simplicity, rapidity and sensitivity without the need for time-consuming separation and tedious preconcentration processes. Additionally, we also found that the bare AgNPs can be directly used as the matrix in MALDI-TOF MS for the analysis of sulfur drugs without the addition of an extra proton source. Copyright (c) 2008 John Wiley & Sons, Ltd. 相似文献