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991.
Predrag Džodić Ljiljana Živanović Ana Protić Mira Zečević Biljana Jocić 《Chromatographia》2009,70(9-10):1343-1351
A chemometrical approach was applied to develop a reversed-phase liquid chromatographic method for simultaneous determination of carbamazepine and its impurities iminostilbene and iminodibenzyl in solid dosage form. According to contemporary literature, no method was developed for simultaneous determination of carbamazepine and these impurities by chemometrical approach. The fractional factorial design was used for selection of variables significantly influencing the chromatographic separation of the investigated substances. The investigated variables were: temperature of the column, the percentage of organic modifier, the acetate buffer concentration and pH of water phase. The first three variables were proved to be significant and were optimized by face centered, central composite design. Investigation was performed using C18 XBridge Shield analytical column (50 mm × 4.6 mm i.d., particle size 3.5 µm). The optimal conditions for the separation were established with the mobile phase composition of methanol–10 mM acetate buffer (pH adjusted to 2.21 with glacial acetic acid) (50:50, v/v) at a flow rate of 1.5 mL min?1, 25 °C column temperature and detection at 260 nm. Total analysis time was shortened to about 8 min. Finally, the method was successfully validated and subsequently applied to the analysis of commercially available carbamazepine tablets. 相似文献
992.
Zorica Vujić Milkica Crevar Vladimir Obradović Vesna Kuntić Snežana Uskoković-Marković 《Chromatographia》2009,70(7-8):1221-1225
A rapid and simple liquid chromatographic method with UV detection has been developed for the determination of hydrochlorothiazide (HCTZ), cilazapril (CL) and its active metabolite cilazaprilat (CLT) in urine. Sample preparation for urine consisted of solid-phase extraction using styrene-divinylbenzene (SDB-2) cartridges. The chromatographic system was a Zorbax Eclipse XDB-C18 column with a mixture of methanol and 10 mM phosphate buffer, pH 2.3 with gradient (20 to 60% of methanol) as mobile phase at a flow rate of 1.0 mL min?1. The detection was performed at the wavelength of 206 nm. Enalapril maleat was used as an internal standard. The detector response was linear in the range of 2.4–30.0, 1.6–15.0 and 1.8–20.0 μg mL?1 for HCTZ, CL and CLT, respectively. LOQ was determined to be 2.4, 1.6 and 1.8 μg mL?1 for HCTZ, CL and CLT, respectively. Both intra- and inter-day precision were within acceptable limits. The method has been applied to urine samples obtained from three hypertensive patients after intake of HCTZ and CL therapeutic dose. 相似文献
993.
Adsorption and reduction of lovastatin were investigated by cyclic and square-wave voltammetry on a hanging mercury drop electrode
in aqueous solutions over a wide pH range (4–9). The electroreduction of lovastatin proceeds via a surface EC mechanism in
the whole pH range investigated. Using adsorptive stripping voltammetry, the drug yielded a well-defined voltammetric response
in Britton-Robinson buffer, pH 6 at −1.49 V which can be used to determine trace amount of lovastatin. The linear concentration
range of application was 1.0 × 10−8–1.0 × 10−7 M by using an accumulation potential of −0.5 V and a 90 s pre-concentration time. The method has been successfully applied
for the determination of lovastatin in a spiked human serum sample. 相似文献
994.
Dzafić E Klein O Screpanti E Hunte C Mäntele W 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,72(1):102-109
NhaA (41,355Da) is a Na(+)/H(+) antiporter of Escherichia coli which plays a central role in regulation of intracellular pH, cellular Na(+) content, and cell volume [E. Padan, S. Schuldiner, J. Exp. Biol. 196 (1994) 443]. Its activity is strongly regulated by pH and increases over 3 orders of magnitude between pH 7 and 8 [A. Rothman, Y. Gerchman, E. Padan, S. Schuldiner, Biochemistry 36 (1997) 14572]. Protein dynamics and flexibility in the activated and inactivated state, respectively, was analysed by probing accessibility in (1)H/(2)H exchange experiments for the wild type and the mutant G338S which is constitutively active independent of pH [A. Rimon, Y. Gerchman, Z. Kariv, E. Padan, J. Biol. Chem. 273 (1998) 26470]. This was studied by ATR-FTIR difference spectroscopy using a home built microvolume (<5 microl) perfusion chamber [E. Agi?, O. Klein, W. M?ntele, Proceedings of the 10th European Conference on the Spectroscopy of Biological Molecules, vol. 93, 2003, ISBN 9634826148; S. Gourion-Arsiquaud, S. Chevance, P. Bouyer, L. Garnier, J.-L. Montillet, A. Bondon, C. Berthomieu, Biochemistry 44 (2005) 8652]. The solution or suspension of the target protein is contained in a chamber with sample volumes of below 5 microl. It is in contact with the ATR crystal and separated from the flowing effector molecules by a dialysis membrane. The flow-ATR unit is characterised by high stability, fast response, and high sensitivity for the IR spectroscopic detection of binding-induced conformational changes and reactions. On the basis of (1)H-(2)H exchange of NhaA followed in the amide I and amide II region of the IR spectrum, it is concluded that the accessible fraction of the polypeptide chain of NhaA increases by more than 10% in the active state. For the mutant, no changes in accessibility were observed for different pH values. The increase of Na(+) concentration increases the extent of exchange. The stability of the wild type protein in the active and inactive form was analysed by measuring the temperature profiles of the IR spectra. A decrease of the structural stability of the protein with activation was observed. Together with the results from (1)H/(2)H exchange, the inactive state represents a more compact form whereas activation induces a more open conformation of the protein. 相似文献
995.
V. Vijayasundaram V. Ramasamy PL. RM. Palaniappan 《Journal of Thermal Analysis and Calorimetry》2009,98(1):183-188
The paper presents the changes in the thermal properties of control, arsenic exposed and DMSA treated Labeo rohita bones by using thermo analytical techniques. The result shows that the mass loss due to the thermal decomposition occurs
in three distinct steps due to loss of water, organic and inorganic materials. The arsenic exposed bones present a different
thermal behaviour compared to the control bones. The residue masses are increased due to arsenic exposure, while the DMSA
treatment reduces the residue mass level. These thermal characteristics can be used as a qualitative method to check the metal
accumulation in samples. 相似文献
996.
Iva Movre Šapić Vesna Volovšek Krešimir Furić Lahorija Bistričić Vladimir Dananić 《Macromolecular Symposia》2011,305(1):122-125
In this work we investigated the solidification of aminopropylsilanetriol dissolved in water (∼25%) under different conditions by Raman spectroscopy. The solidification was carried out at three different temperatures 8 °C, 23 °C and 60 °C. The influence of electromagnetic radiation on the polymerization process was also studied. Samples were held to solidify in dark and at UV (254 nm and 356nm) spectral range. In order to investigate the influence of the substrate on the resulting polymer structure, teflon, PVC, glass, brass and silica were used. Best ordered polymerized structure was achieved for samples deposited on plastics and solidified in dark, at room temperature. 相似文献
997.
Using a fixed point relation of the square-root type and the basic fourth-order method, improved methods of fifth and sixth order for the simultaneous determination of simple zeros of a polynomial are obtained. An increase in convergence is achieved without additional numerical operations, which points to high computational efficiency of the accelerated methods. The main aim of this work is the convergence analysis of improved simultaneous methods given under computationally verifiable initial conditions in the spirit of Smale’s point estimation theory. 相似文献
998.
Starting from the Strassen method for rapid matrix multiplication and inversion as well as from the recursive Cholesky factorization algorithm, we introduced a completely block recursive algorithm for generalized Cholesky factorization of a given symmetric, positive semi-definite matrix A∈Rn×n. We used the Strassen method for matrix inversion together with the recursive generalized Cholesky factorization method, and established an algorithm for computing generalized {2,3} and {2,4} inverses. Introduced algorithms are not harder than the matrix–matrix multiplication. 相似文献
999.
1000.