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91.
Elaheh Nourbala Tafti Ali Mohammad Haji Shabani 《International journal of environmental analytical chemistry》2017,97(5):444-455
A simple, sensitive and reliable method has been developed for separation and preconcentration of chromium (VI) from aqueous samples before determination by electrothermal atomic absorption spectrometry. The method is based on the extraction of the hydrophobic complex of chromium (VI) with ammonium pyrrolidine dithiocarbamate in the coacervates made up of decanoic acid reverse micelles in the water–tetrahydrofuran mixture. Parameters affecting the extraction efficiency of the analyte were studied and optimised. Under the optimum conditions, the linear range, enhancement factor, the limit of detection and limit of quantification were found to be 0.008–0.4 µg L?1, 127, and 1.8 ng L?1 and 6.0 ng L?1, of Cr(VI), respectively. The relative standard deviation at the concentration level of 0.1 µg L?1 Cr(VI) (n = 6) was 4.2%. Total chromium was determined after the oxidation of Cr(III) to Cr(VI) with permanganate in acidic medium. The method was successfully applied to the determination of chromium species in water and human serum samples. 相似文献
92.
Elahe Kazemi Ali Mohammad Haji Shabani Parisa Sadat Hashemi 《International journal of environmental analytical chemistry》2017,97(8):743-755
This study describes the successful sequential modification of multi-walled carbon nanotube (MWCNT) by Fe3O4 magnetic nanoparticles and 2-mercaptobenzothiazole (MBT) followed by its application as a novel sorbent for simultaneous magnetic solid phase microextraction of lead and cadmium. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the chemical surface modification of the MWCNT. The ions retained on the 2-MBT/magnetic nanoparticles modified MWCNTs were eluted with 1.0 mL of nitric acid (0.8 mol L?1) in methanol solution and determined by the flame atomic absorption spectrometry. All parameters affecting the extraction condition were thoroughly investigated and optimised. Under the optimised condition preconcentration factor of 150.0, enhancement factors of 149.0 and 149.2 and limits of detection of 0.21 and 0.01 µg L?1 were achieved for lead and cadmium, respectively. Using the prepared magnetic nanocomposite, the possible interference of other common ions associated with lead and cadmium determination was effectively avoided and the method was successfully applied to the simultaneous determination of the target ions in various environmental water samples. 相似文献
93.
This paper deals with problems of computing possible values of latest starting times and determining types of criticality for all activities in a network with interval or fuzzy activity durations. Although the problem of computing the latest starting times has been solved, a novel polynomial algorithm which is easy to understand and improves complexity is proposed. 相似文献
94.
Preconcentration of valsartan by dispersive liquid–liquid microextraction based on solidification of floating organic drop and its determination in urine sample: Central composite design 下载免费PDF全文
Arezou Amiri Pebdani Ali Mohammad Haji Shabani Shayesteh Dadfarnia Mohammad Sharif Talebianpoor Saeid Khodadoust 《Journal of separation science》2016,39(10):1935-1944
In this work, a fast, easy, and efficient dispersive liquid–liquid microextraction method based on solidification of floating organic drop followed by high‐performance liquid chromatography with UV detection was developed for the separation/preconcentration and determination of the drug valsartan. Experimental design was applied for the optimization of the effective variables (such as volume of extracting and dispersing solvents, ionic strength, and pH) on the extraction efficiency of valsartan from urine samples. The optimized values were 250.0 μL ethanol, 65.0 μL 1‐dodecanol, 4.0% w/v NaCl, pH 3.8, 1.0 min extraction time, and 4.0 min centrifugation at 4000 rpm min?1. The linear response (r2 = 0.997) was obtained in the range of 0.013–10.0 μg mL?1 with a limit of detection of 4.0 ng mL?1 and relative standard deviations of less than 5.0 % (n = 6). 相似文献
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Hassan Haji Hosseini Mojeni Mohammad Reza Shojaei 《Journal of Experimental and Theoretical Physics》2020,131(6):910-916
Journal of Experimental and Theoretical Physics - Due to the absence of the free neutron target, the form factors or the structure function of the neutron directly cannot be obtained from the... 相似文献
98.
Under the organomagnesium complex n‐Bu2CH3MgLi conditions, picoline compounds provide a new entry to a broad range of polyfunctional picoline derivatives, after reaction with various electrophiles. 相似文献
99.
A highly effective and mild protocol for ring opening of epoxides with NH 4 SCN in the presence of catalytic amount of a multisite phase-transfer catalyst, α,α',α" -N-hexakis(triethylammoniummethylene chloride)-melamine, is developed. A variety of b-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times. 相似文献
100.
We study a five-dimensional spacetime admitting, in the presence of torsion, a non-degenerate conformal Killing–Yano 2-form which is closed with respect to both the usual exterior differentiation and the exterior differentiation with torsion. Furthermore, assuming that the torsion is closed and co-closed with respect to the exterior differentiation with torsion, we prove that such a spacetime is the only spacetime given by the Chong–Cvetič–Lü–Pope solution for stationary, rotating charged black holes with two independent angular momenta in five-dimensional minimal gauged supergravity. 相似文献