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261.
The first study on the high efficiency of nano-structured lead dioxide as a new fiber for solid-phase microextraction (SPME) purposes has been reported. The size of the PbO2 particles was in the range of 34-136 nm. Lead dioxide-based fibers were prepared via electrochemical deposition on a platinum wire. The extraction properties of the fiber to benzene, toluene, ethylbenzene, and xylenes (BTEX) were examined using headspace solid-phase microextraction (HS-SPME) mode coupled to gas chromatography-flame ionization detection (GC-FID). The results obtained proved the suitability of proposed fibers for the sampling of organic compounds from water. The extraction procedure was optimized by selecting the appropriate extraction parameters, including preparation conditions of coating, salt concentration, time and temperature of adsorption and desorption and stirring rate. The calibration graphs were linear in a concentration range of 0.1-100 microg l(-1) (R2 > 0.994) with detection limits below 0.012 microg l(-1) level. Single fiber repeatability and fiber-to-fiber reproducibility were less than 10.0 and 12.5%, respectively. The PbO2 coating was proved to be very stable at relatively high temperatures (up to 300 degrees C) with a high extraction capacity and long lifespan (more than 50 times). Higher chemical resistance and lower cost are among the advantages of PbO2 fibers over commercially available SPME fibers. Good recoveries (81-108%) were obtained when environmental samples were analyzed. 相似文献
262.
This article presents a connection between fuzzy preordered structures and hyperstructures. Firstly, we introduce the notion of fuzzy preordered semigroup and then, we construct a semihypergroup associated with it, giving some properties of the associated hyperstructure. Secondly, we define the notion of fuzzy preordered ring in order to construct a fuzzy hyperring. 相似文献
263.
Fazlollah Soleymani B. S. Mousavi 《Computational Mathematics and Mathematical Physics》2012,52(2):203-210
In this paper, we establish two new classes of derivative-involved methods for solving single valued nonlinear equations of
the form f(x) = 0. The first contributed two-step class includes two evaluations of the function and one of its first derivative where
its error analysis shows a fourth-order convergence. Next, we construct a three-step high-order class of methods including
four evaluations per full cycle to achieve the seventh-order of convergence. Numerical examples are included to re-verify
the theoretical results and moreover put on show the efficiency of the new methods from our classes. 相似文献
264.
In this paper we obtain topological static solutions of some kind of pure F(R) gravity. The present solutions are two kind: first type is uncharged solution which corresponds with the topological (a)dS
Schwarzschild solution and second type has electric charge and is equivalent to the Einstein-Λ-conformally invariant Maxwell
solution. In other word, starting from pure gravity leads to (charged) Einstein-Λ solutions which we interpreted them as (charged)
(a)dS black hole solutions of pure F(R) gravity. Calculating the Ricci and Kreschmann scalars show that there is a curvature singularity at r = 0. We should note that the Kreschmann scalar of charged solutions goes to infinity as r → 0, but with a rate slower than that of uncharged solutions. 相似文献
265.
Mir Fazlollah Mousavi Mohsen Barzegar Abdolvahed Rahmani Ali Jabbari 《Mikrochimica acta》2002,140(1-2):41-44
A new, simple photometric method for the determination of palladium was described. Palladium was determined photometrically
at 600 nm and pH = 5.4 based on its heterogeneous catalytic effect on the reduction of thionine (TN) with hypophosphite (HP)
using a probe-type photometer system (variable time method). The influence of reaction variables was discussed. The calibration
curve was found linear in the range 0.11–5.55 μg/ml (at 30 °C) and the detection limit was 0.06 μg/ml. The relative standard
deviation of the developed method was 1.6% (for 10 replicate determinations of 2.22 μg/ml Pd(II)). The effect of interference
from other metal ions and anions was studied. The proposed method was successfully applied to catalysts, Pd–C, Al–Si–Pd (new
and used).
Received March 1, 2001 Revision August 10, 2001 相似文献
266.
A cloud point extraction process using mixed micelle of the cationic surfactant CTAB and non-ionic surfactant TritonX-114 to extract uranium(VI) from aqueous solutions was investigated. The method is based on the color reaction of uranium with pyrocatechol violet in the presence of potassium iodide in hexamethylenetetramine buffer media and mixed micelle-mediated extraction of complex. The optimal extraction and reaction conditions (e.g. surfactant concentration, reagent concentration, effect of time) were studied and the analytical characteristics of the method (e.g. limit of detection, linear range, preconcentration, and improvement factors) were obtained. Linearity was obeyed in the range of 0.20-10.00 ng mL−1 of uranium(VI) ion and the detection limit of the method is 0.06 ng mL−1. The interference effect of some anions and cations was also tested. The method was applied to the determination of uranium(VI) in tap water, waste-water and well water samples. 相似文献
267.
A simple, rapid and sensitive flow injection spectrophotometric method for determination of selenium (0.005-1.5 mug ml(-1)) is described. The method is based on the catalytic effect of Se(IV) on the reduction reaction of thionine (TN) with sulphide ion, monitored spectrophotometrically at 598 nm. The detection limit is 5 ng ml(-1) the relative standard deviation for eight replicate measurements is 1.1% for 1 mug ml(-1) of selenium. The sampling rate is 25-30 samples h(-1). The procedure was applied successfully to the determination of selenium in real samples. 相似文献
268.
A membrane electrode selective to hexadecylpyridinium bromide was used to study the micellization of the surfactant in the presence of varying concentrations of crown ethers 15-crown-5, dicyclohexyl-18-crown-6 and dicyclohexyl-24-crown-8 at 27°C. The critical micelle concentration of surfactant was largely influenced by the crown ethers used, indicating their participation in the structure of the resulting micelle. The degree of attachment of crown ethers to the surfactant in the micellar structure was found to be 1. An estimation of the Kf for the 1:1 surfactant-crown interaction in the micellar region is reported. The degree of counter ion dissociation was found to increase with the crown ether concentration, and with the nature of macrocyclic ligands in the order 15-crown-5 < dicyclohexyl- l8-crown-6 < dicyclohexyl-24-crown-8. There was also some evidences for a rather strong interaction between dicyclohexyl-24-crown-8 and the surfactant in the submicellar concentration ranges in solution. 相似文献
269.
A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters. 相似文献
270.
Mixed-level orthogonal array design for the optimization of solid-phase extraction of some pesticides from surface water 总被引:1,自引:0,他引:1
Bagheri H Saraji M Chitsazan M Mousavi SR Naderi M 《Journal of chromatography. A》2000,888(1-2):197-208
An orthogonal array design (OAD), OA32(4(1) x 2(28)), was employed as a chemometric method for the optimization of the solid-phase extraction (SPE) of atrazine, diazinon, ametryn and fenthion in surface water. Seven parameters: the type of eluting solvent, type of sorbent, flow-rate of eluting solvent, sample pH, sample volume, elution volume, addition of modifier and flow-rate of water sample were studied and optimized by a mixed-level OAD. The effects of these factors and some two-variable interactions on the recovery of the pesticides were quantitatively evaluated by the analysis of variance and percentage contribution techniques. The final optimized condition was employed for the SPE of selected micro-organic pollutants from Karoun river water, south of Iran. Atrazine and ametryn were tentatively identified and determined at the 0.7 and 0.9 microg l(-1) level, respectively. 相似文献