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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.
Chao Niu Adila Tuerxuntayi Gen Li Madina Kabas Chang-Zhi Dong Haji Akber Aisa 《中国化学快报》2017,28(7):1533-1538
The Vernohia anthelmintica L.'s extract is one of the most popular Uygur medicines used for vitiligo. It is believed that the chalcone compounds of the plant play an important role in the treatment since they may activate tyrosinase and improve melanin production. In this study, twenty-one chalcones and nine analogues were synthesized in view of three different components of chalcone(A, B ring and a,b-unsaturated carbonyl). After biological evaluation of their activity on tyrosinase in cell-free systems,the result showed that most compounds(except polyhydroxy chalcones) possess activator effect on the tyrosinase, especially for 13a–15a, 20 a and 1b, which bearing a comparable activity to the positive control8-MOP. SAR of these tyrosinase activator was summed up for the first time as well. Finally, compound 13 a was found to increase melanin contents and tyrosinase activity 1.75 and 1.3 fold, respectively, compared with that of untreated murine B16 cells at the concentration of 40 mg/m L. 相似文献
94.
Frequency and amplitude perturbation analysis of electroglottograph during sustained phonation 总被引:3,自引:0,他引:3
T Haji S Horiguchi T Baer W J Gould 《The Journal of the Acoustical Society of America》1986,80(1):58-62
Electroglottography (EGG) was used to monitor vocal fold vibration patterns in normal subjects and patients with various laryngeal disorders. In order to evaluate the regularity of vocal fold vibration, frequency and amplitude perturbation of EGG waves during sustained phonation were measured with a laboratory computer. The data were compared to the degree of hoarseness evaluated by auditory perception and by sound spectrographic analysis. Frequency and amplitude perturbation measures showed some overlap between normal and pathological groups. However, there was a close relation between perturbation analysis of EGG waves and degree of hoarseness (Spearman's rank correlation coefficient rs = 0.73, p less than 0.0005). Amplitude perturbation was found to be a more sensitive measure of the irregularity of vocal fold vibration than frequency perturbation. 相似文献
95.
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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98.
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
99.
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
100.
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