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51.
A new approach for the development of a dispersive liquid–liquid microextraction followed by GC with flame ionization detection was proposed for the determination of phthalate esters and di‐(2‐ethylhexyl) adipate in aqueous samples. In the proposed method, solid and liquid phases were used as the disperser and extractant, respectively, providing a simple and fast mode for the extraction of the analytes into a small volume of an organic solvent. In this method, microliter levels of an extraction solvent was added onto a sugar cube and it was transferred into the aqueous phase containing the analytes. By manual shaking, the sugar was dissolved and the extractant was released into the aqueous phase as very tiny droplets to provide a cloudy solution. Under optimized conditions, the proposed method showed good precision (RSD less than 5.2%), high enrichment factors (266–556), and low LODs (0.09–0.25 μg/L). The method was successfully applied for the determination of the target analytes in different samples, and good recoveries (71–103%) were achieved for the spiked samples. No need for a disperser solvent and higher enrichment factors compared with conventional dispersive liquid–liquid microextraction and low cost and short sample preparation time are other advantages of the method.  相似文献   
52.
Journal of Thermal Analysis and Calorimetry - The ultimate goal of the present review paper is to summarize and discuss the findings of the most recently published literature on natural convection...  相似文献   
53.
An efficient and straightforward procedure has been developed for the synthesis of highly substituted mono- and bis-N-aryl-3-aminodihydropyrrol-2-one-4-carboxylates via a one-pot, four-component domino reaction of amines, dialkyl acetylenedicarboxylates and formaldehyde in the presence of InCl3 (20 mol%) in MeOH at ambient temperature. The salient advantages of this method are mild reaction conditions, environmentally benign, high to excellent yields, shorter reaction times, easy operation and no column chromatographic separation.  相似文献   
54.
In the present work,an easy solid phase extraction method using alumina modified with polyethylenimine as a new adsorbent was applied to the simultaneous extraction of copper,silver,and palladium ions prior to their determination with electrothermal atomic absorption spectrometry.The analytical procedure involved the complex formation of these cations with polyethylenimine as a chelating agent in buffer media of pH 7.0.Under the optimum conditions,a preconcentration factor of200,150,and 200,precision of ±5.4%,±4.7%,and ±5.2%and linear calibration ranges of 15.0-140,4.0-93,and 7.5-125 ng/L(in original solution) for Cu,Ag,and Pd were obtained,respectively.Also detection limits of3.9,1.1,and 2.0 ng/L were obtained for Cu,Ag,and Pd,respectively.The proposed method was applied to the determination of copper,silver,and palladium in some real samples with satisfactory results.  相似文献   
55.
A mathematical model for the input-output functions of the hearing aids is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output when the input is formed of multitone large sound pressure levels. The special case of two-tone equal-amplitude incident pressure level is considered in detail. The results show that the third-order intermodulation component is always higher than the third-harmonic component. The results also show that the input-output functions exhibiting peak clipping exhibit the worst harmonic and intermodulation performance for large sound pressure levels. The simple wide-dynamic range compression (WDRC) input-output function exhibits the best harmonic and intermodulation distortion performance under large sound pressure levels. These results are consistent with the previously reported observations and reveal that there is a correlation between intelligibility of high-level speech and the harmonic and intermodulation performance of the hearing aid under large sound pressure levels.  相似文献   
56.
57.
A detailed mathematical derivation and an experimental characterization of one to two ratio rotating polarizer analyzer ellipsometer (RPAE) are presented. The alignment, calibration, and testing of reference samples are also discussed. The optical properties of some known materials obtained by the proposed ellipsometer will be shown and compared to accepted values. Moreover, the constructed ellipsometer will be tested using two ellipsometry standards with different thicknesses.  相似文献   
58.
Taher MA 《Talanta》2000,52(2):181-188
Zinc is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylamminophenol (5-BrPADAP)-ammonium tetraphenylborate with microcrystalline naphthalene or by a column method in the pH range 7.5-9.0 from a large volume of aqueous solutions of various samples. After filtration, the solid mass consisting of the zinc complex and naphthalene was dissolved with 5 ml of dimethylflarmamide and the metal was determined by atomic absorption spectrometry. Zinc complex can alternatively be quantitatively adsorbed on ammonium tetrphenylborate-naphthalene adsorbent packed in a column and determined similarly. The calibration curve is linear 0.05-4.0 ppb in dimethylformamide solution. Eight replicate detenninations of 1.0 ppb of zinc gave a mean absorbance of 0.124 with a relative standard deviation of 1.3%. The sensitivity for 1% absorption was 0.035 ppb. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the trace determination of zinc in various standard samples.  相似文献   
59.
 Protonation of the reactive intermediate produced in the reaction between pyridine and dialkyl acetylenedicarboxylates by strong CH-acids such as N,N′-dimethylbarbituric acid, Meldrum’s acid, or indane-1,3-dione leads to a vinylpyridinium cation which undergoes an addition reaction with the enolate anion of the CH-acid to produce stable 1,4-diionic pyridinium betaines in good yields.  相似文献   
60.
This paper aims to introduce an analytic technique, namely the Homotopy perturbation method (HPM) for the solution of integro-differential equations. From the computational viewpoint, the comparison shows that the homotopy perturbation method is efficient and easy to use.  相似文献   
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