Partial least-squares regression for the simultaneous determination of aluminum and beryllium in geochemical samples using xylenol orange

A partial least-squares regression (PLS) was developed for the simultaneous spectrophotometric determination of aluminum and beryllium in geochemical samples by xylenol orange as the chromogenic reagent in water media and in micellar media. The effects of pH, xylenol orange concentration and surfactant concentration on the complexes formation reactions were studied. In the absence of surfactant the complex color development takes place at 2 h after mixing the reagents. By using CTAB as micellar media the complexes formation was improved and the rate of the complexation reactions increased. By using PLS-1 algorithm satisfactory results were obtained. The proposed procedure showed to be useful for prediction of Al and Be values from 0.1 to 1.0 mg L(-1).     

N-Bromo Reagent Mediated Oxidation of Urazoles to Their Corresponding Triazolinediones under Mild and Heterogeneous Conditions

Various N-bromo reagents [HMTAB, DABCO-bromine, DPTBE, and TBCA] were used as effective oxidizing agents for the oxidation of urazoles and bisurazoles to their corresponding triazolinediones under mild and heterogeneous conditions at room temperature with good to excellent yields. Also the oxidation of some new 4-phenylurazole derivatives with these reagents is discussed.     

Kinetic study of charge transfer complexes of ICl3 with DB18C6 and DC18C6 in some nonaqueous solvents

The spectrophotometric kinetic charge–transfer complex formation of iodine trichloride (ICl₃) with Dibenzo-18-crown-6 (DB18C6), Dicyclohexyl-18-crown-6 (DC18C6) has been studied in chloroform; dichloromethane and propylene carbonate solutions at different temperatures. The results indicated immediate formation of an electron donor–electron acceptor complex; which is followed by two relatively slow consecutive reactions. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance–time data to appropriate equations. The influences of both the crown’s structure and the solvent properties on the formation of donor–electron acceptor complexes and the rates of subsequent reactions are discussed.     

PEG-N2O4: An Efficient Nitrating Agent for the Selective Mono- and Dinitration of Phenols Under Mild Conditions

N₂O₄ was easily impregnated on polyethyleneglycol to give a stable reagent. The polyethyleneglycol-N₂O₄ (PEG-N₂O₄) system was used as an effective nitrating agent for the nitration of phenols. Mono- and dinitrophenols can be obtained via direct nitration of phenols in the presence of PEG-N₂O₄ at room temperature in moderate to high yields.     

Simultaneous spectrophotometric determination of Sn(II) and Sn(IV) by mean centering of ratio kinetic profiles and partial least squares methods

Two spectrophotometric methods are described for the simultaneous determination of binary mixtures of Sn(II) and Sn(IV) in water samples and fruit juice samples, without prior separation steps, using the mean centering of ratio kinetic profiles and partial least squares (PLS) methods. The methods are based on the difference in the rate of the reactions of Sn(II) and Sn(IV) with pyrocatechol violet at pH 4.0. The methods allow rapid and accurate determination of Sn(II) and Sn(IV). The analytical characteristics of the methods for the simultaneous determination of binary mixtures of Sn(II) and Sn(IV) were calculated. The results showed that the methods were capable to simultaneous determination of 0.1–1.80 mg L⁻¹ each of cations. The proposed methods were successfully applied to the simultaneous determination of Sn(II) and Sn(IV)in an orange juice sample.     

Spectrophotometric determination of bismuth in water samples after preconcentration of its thiourea-bromide ternary complex on activated carbon

A simple, accurate, sensitive and reliable method for the selective extraction and spectrophotometric determination of Bi(III) was developed. Bi(III) was collected on activated carbon after complexation with thiourea and bromide ion in acidic media. The complex retained on activated carbon was then desorbed with the bromide solution in N,N-dimethylformamide (DMF) and determined spectrophotometrically at 375 nm. The linear calibration ranges and limit of detection for the proposed method was 1.00×10⁻⁹-1.50×10⁻⁷ and 8.00×10⁻¹⁰ mol l⁻¹, respectively. The influence of the interfering cations and anions on the determination of bismuth was investigated. The method was successfully applied to the extraction and determination of bismuth in natural water samples.     

Chemically modified alumina nanoparticles for selective solid phase extraction and preconcentration of trace amounts of Cd(II)

We have developed a solid phase extraction method for the determination of cadmium ions in aqueous samples. It is based on the adsorption of Cd(II) on alumina nanoparticles coated with sodium dodecyl sulfate and modified with a newly synthesized Schiff base. Analytical parameters such as pH value, amount of adsorbent, type and concentration of eluent, flow rates of the sample and eluent, sample volume and matrix effects were optimized. Desorption is accomplished with 2?mol?L^?1 nitric acid. Cd(II) was then determined by flame atomic absorption spectrometry. The maximum enrichment factor is 75. Under the optimum experimental conditions, the detection limit is 0.14???g?L^?1 in original solution. The adsorption capacity of the modified sorbent is 4.90?mg?g^?1 for cadmium ions. The method was applied to the determination of trace quantities of Cd(II) in water, wastewater, and biological and food samples with satisfactory results.

Interaction of benzene-1,3-disulfonylamid-kriptofix[22] with iodine in chloroform and dichloromethane solutions

The interaction of iodine as an cr-acceptor with a synthetic ligand,benzene-1,3-disulfonylamid-kriptofix[22]（BDSAK） as a π-donor has been investigated spectrophotometrically in chloroform（CHCl3） and dichloromethane（DCM） solutions.The results of mole ratio plots and Job＇s method show the stoichiometry of complexation I2/BDSAK is 1：1.Stability constants have been calculated in various temperatures and thermodynamic parameters have also been determined from the temperatures dependence of the stability constants by using van＇t Hoff equation.The results indicate the iodine complex with BDSAK is enthalpy stabilized but entropy destabilized.     

PEG‐N2O4 System as an Efficient Reagent both for the Rapid Oxidation of Urazoles and 1,4‐Dihydropyridines under Nonaqueous Conditions

N₂O₄ was easily impregnated on polyethyleneglycol to give a stable reagent. Polyethyleneglycol‐N₂O₄ ( PEG‐N₂O₄ ) system was used as an effective oxidizing agent for the oxidation of urazoles and bis‐urazoles to their corresponding triazolinediones and also for the aromatization of 1,4‐dihydropyridines into the corresponding pyridine derivatives under mild conditions at room temperature with good to excellent yields.