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71.
Bhim Bali Prasad Khushaboo Tiwari Meenakshi Singh Piyush S. Sharma Amit K. Patel Shrinkhala Srivastava 《Chromatographia》2009,69(9-10):949-957
A combination approach in solid-phase microextraction, based on a molecularly imprinted polymer-brush coating on an optical fiber coupled with a complementary molecularly imprinted polymer sensor, has been adopted for isolation, preconcentration, and analysis of dopamine at ultratrace levels in highly dilute aqueous samples. This combination enabled enhanced (up to 8.5-fold) preconcentration of the analyte, which is appropriate for achieving a stringent detection limit in clinical diagnosis of several neurodegenerative diseases. The detection limit of dopamine in biological samples was 0.018 ng mL?1 with a relative standard deviation less than 2.1% and without any non-specific contributions. 相似文献
72.
Ashish Kumar Yahya E. Jad Ayman El-Faham Beatriz G. de la Torre Fernando Albericio 《Tetrahedron letters》2017,58(30):2986-2988
Herein, we report the use of γ-valerolactone (GVL) and N-formylmorpholine (NFM) as DMF substitutes in polystyrene based SPPS. The solubility of selected amino acids and coupling reagents were studied in GVL and NFM, followed by their use in the successful synthesis of Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH2) and Aib-ACP decapeptide (H-Val-Gln-Aib-Aib-Ile-Asp-Tyr-Ile-Asn-Gly-NH2). 相似文献
73.
Preparation of electrodeless discharge lamps for emission studies of uranium isotopes at trace level
G.K. Bhowmick R. Verma M.K. Verma V.A. Raman A.R. Joshi M.N. Deo L.M. Gantayet A.K. Tiwari K.L. Ramakumar Navin Kumar 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010,65(12):1047-1051
A simplified method for preparation of electrodeless discharge lamp for uranium isotopes with specific concerns for 232U is described. Micro-gram quantities of solid uranium oxides and aqueous solution of uranium nitrate have been used as a starting material for in situ synthesis of uranium tetraiodide. High temperature iodination reaction is carried out in the presence of inert gas neon. By careful design, the preparation time and surface area of quartz reaction tubes have been reduced considerably. The latter decreases the level of contamination which has a direct bearing on the operational lifetime of the lamps. Incorporation of steps to purify the product from an unwanted material improved the stability of the lamps. The procedure provides a safe and convenient way of handling 232U in particular but can be extended in general to any actinides having radioactivity similar to that of freshly separated 232U. Characteristic emission of uranium isotopes have been recorded by Fourier Transform Spectrometer to show the satisfactory operation of the lamps as well as their usage for studying emission spectra of the specific isotope. 相似文献
74.
X-ray field intensity generated over a multilayer surface during a strong Bragg reflection condition has been used to analyze the particulate matter deposited on its surface, for the average particles size distribution and detection sensitivity of various elements. The elemental detection sensitivities achieved at Bragg reflection condition are compared to those obtained at incidence angles below critical angle, under total external reflection condition. The results obtained indicate that when big size particles (> 1 μm) are distributed over a large surface area, the observed fluorescence yields deteriorate by 15–18% in the total external reflection condition, due to strong sample absorption effects. In such a case, use of a multilayer mirror as a sample carrier and fluorescence excitation under Bragg reflection condition provides better fluorescence yield and hence improved detection sensitivity for an element. 相似文献
75.
X‐ray standing wave (XSW) field generated under Bragg reflection condition in a periodic Mo/Si multilayer structure has been used to determine the concentration and location of various trace element contaminants embedded in different layers of that multilayer structure. We have used intense synchrotron X rays for XSW analysis. It is observed that various trace element impurities such as Cr, Fe, Ni and W get embedded unintentionally in the multilayer structure during the deposition process. Consequences of such impurity incorporation on the optical properties of the multilayer structure are discussed in hard and soft X‐ray regions. Present measurements are important in order to optimize the deposition methods on one hand and to better correlate the measured optical properties of a multilayer structure with theoretical models on the other. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
76.
Kishore K. Tiwari 《中国化学会会志》2010,57(1):105-110
A new simple and sensitive and selective spectrophotometric method has been developed for the determination of ascorbic acid (AA) at trace level using a new reagent, leuco malachite green (LMG). AAreacts with potassium iodide‐iodate solution under acidic conditions to liberate iodine and the liberated iodine selectively oxidizes LMG to MG dye. The colour of the dye was measured at 620 nm. Beer's law is obeyed over the concentration range of 0.8–8 iμg μAA per 25 mL of final solution (0.032–0.32 ppm). The apparent molar absorptivity and Sandell's sensitivity of the method were found to be 2.98 × 105 l mol−1 cm−1, 0.0042 μg cm−2, and respectively. Statistical treatment of the experimental results indicates that the method is precise and accurate. The method is free from interference of common ions and many of the ingredients commonly found in pharmaceuticals. The reliability of the method was established by parallel determination against Leucocrystal violet (LCV) method. The method described was satisfactorily applied for the determination of AA in fruit juices, pharmaceuticals and biological samples. 相似文献
77.
Ashish Kumar Jindal Lawrence Overzet Matthew Goeckner 《Plasma Chemistry and Plasma Processing》2010,30(2):287-297
Pulsed plasmas containing organic precursors are becoming increasingly common for multiple applications. To understand the
nature of such discharges, in-situ time resolved microwave interferometry measurements of the electron density in a 60 W pulsed
inductively coupled 1,3-butadiene discharge have been made. Measurements were also made for continuous wave plasmas at 40,
50, 60 and 70 W power for comparison. The data shows that the time averaged electron densities are independent of pulse width
at a particular duty cycle. In addition, time averaged values increase approximately linearly with increasing duty cycle.
Such linearity in average density is tied to the ambipolar loss rate. This knowledge is important for understanding the growth
kinetics of plasma polymerized films. 相似文献
78.
Chlorella minutissima—A Promising Fuel Alga for Cultivation in Municipal Wastewaters 总被引:1,自引:0,他引:1
Ashish Bhatnagar Monica Bhatnagar Senthil Chinnasamy K. C. Das 《Applied biochemistry and biotechnology》2010,161(1-8):523-536
It is imperative to slash the cost of algal oil to less than $50 bbl?1 for successful algal biofuel production. Use of municipal wastewater for algal cultivation could obviate the need for freshwater and the nutrients—N and P. It would also add CO2 through bacterial activity. Chlorella minutissima Fott et Nova dominated the entire phycoflora year around and through each stage of the wastewater treatment at the oxidation pond system of Wazirabad (Delhi) in India. The ability to grow so profusely in such varied and contrasting situations made this alga unique. Besides pollution tolerance, it grew heterotrophically in dark under acidic conditions and as a mixotroph in presence of light over a range of organic C substrates. It could utilize both ammoniacal and nitrate nitrogen, survived anaerobicity, 5% NaCl and ?10 bar of osmotic stress. C. minutissima grew at pH 4–11 and raised the pH set initially by 1 to 3 units in 7.5 h. It showed gigantism and largely kept afloat in presence of utilizable organic carbon, while flocculated in mineral medium and on aging. The alga also possessed potential for biofuel production. The studied parameters indicate why C. minutissima was a potential biomass builder in municipal sewage and could be used to determine which other alga(e) may serve the purpose. 相似文献
79.
Ashutosh Tiwari Rajendra Kumar Mani Prabaharan Ravi R. Pandey Premlata Kumari Anurag Chaturvedi A. K. Mishra 《先进技术聚合物》2010,21(9):615-620
A nanofibrous polyaniline (PANI) thin film was fabricated using plasma‐induced polymerization method and explored its application in the fabrication of NO2 gas sensor. The effects of substrate position, pressure, and the number of plasma pulses on the PANI film growth rate were monitored and an optimum condition for the PANI thin film preparation was established. The resulting PANI film was characterized with UV–visible spectrophotometer, FTIR, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The PANI thin film possessed nanofibers with a diameter ranging from 15 to 20 nm. The NO2 gas sensing behavior was studied by measuring the change in electrical conductivity of PANI film with respect to NO2 gas concentration and exposure time. The optimized sensor exhibited a sensitivity factor of 206 with a response time of 23 sec. The NO2 gas sensor using nanofibrous PANI thin film as sensing probe showed a linear current response to the NO2 gas concentration in the range of 10–100 ppm. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
80.
Reenamoni Saikia Chaliha K. Annapurna Anal Tarafder V.S. Tiwari P.K. Gupta Basudeb Karmakar 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(1):243-250
Precursor glass of composition 25K2O–25Nb2O5–50SiO2 (mol%) doped with Er2O3 (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO3 nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO3 estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO3 phase. The measured visible photoluminescence spectra have exhibited green emission transitions of 2H11/2, 4S3/2 → 4I15/2 upon excitation at 377 nm (4I15/2 → 4G11/2) absorption band of Er3+ ions. The near infrared (NIR) emission transition 4I13/2 → 4I15/2 is detected around 1550 nm on excitation at 980 nm (4I15/2 → 4I11/2) of absorption bands of Er3+ ions. It is observed that photoluminescent intensity at 526 nm (2H11/2 → 4I15/2), 550 nm (4S3/2 → 4I15/2) and 1550 nm (4I13/2 → 4I15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τf) of the 4I13/2 → 4I15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er3+ ions gradually enter into the KNbO3 nanocrystals. 相似文献