Annali di chimica最新文献

Photocatalytic degradation of benzylamine and aniline on TiO₂, Pt-modified TiO₂, ZnO and ZnS in aqueous solution has been investigated. The degradation of the compounds follows a pseudo-first-order kinetics according to Langmuir-Hinshelwood model. The degradation process of benzylamine and aniline was evaluated by ninhydrin spectrophotometric method using UV-visible spectrophotometer in λmax= 538 and 525 nm, respectively. The results showed the order of Pt/TiO₂> TiO₂> ZnO> ZnS for photocatalytic activity. In addition increasing of the Pt-loading was found to enhance the degradation rate of the compounds up to the optimal amount of 5wt. % onto the surface of TiO₂ so that the rates of degradation were increased about two times. Rate constants for photodegradation of benzylamine and aniline were found to be 1.4×10^-3 min^-1 and 0.7×10^-3 min^-1 for TiO₂ as photocatalyst, while 2.7×10^-3 min^-1 and 1.7×10^-3min^-1 for (5 wt.%) Pt/TiO₂ as photocatalyst. Running the reactions in various pH (5-11), indicated that the pH= 8 and 10 or Higher are the optimum pH for photocatalytic degradation of benzylamine and aniline respectively. The effects of some other parameters such as amount of photocatalyst, flux of oxygen and irradiation time were evaluated. Furthermore, the Langmuir-Hinshelwood rate constant k_r and adsorption constant K_A for the titled compounds are reported.

The construction and general performance characteristics of a novel potentiometric PVC membrane sensor based on pethidine-phosphomolybdate as electroactive material for the determination of pethidine are described. This sensor exhibits fast, stable and near-Nernstain response 55.24±0.1, over the concentration range 1.10^-2-1.10^-5M for pethidine-phosphomolybdate over pH 2-7. No interferences are caused by many organic, inorganic cations, alkaloids and amino acids. The sensor proved useful for determining pethidine in pure forms, pharmaceutical injections and monitoring the content uniformity assay of ampoules. The designed sensor also show good accuracy for the determination of pethidine in biological fluids.

The investigation on calcium (II) oxalate is carried out in order to study its solubility in different ionic media. In the same conditions the protonation constants of oxalate and the stability of complex species have been determined. As the stoichiometric composition of the solid calcium (II) oxalate prepared for the investigation was accurately checked, the salt CaC₂O₄ · H₂O is proposed as universal (chelometry, redox, acidimetry) standard. Results of titrations support this possibility.

A novel macroporous resin was prepared from an epoxy resin and triethylenetetramine (TETA) via a polymerization using micro-phase separation. In this novel method the polyethylene glycol (PEG-400) was used as solvent in the initial stage and a phase-separation reagent at later stage of the polymerization was firstly adopted. The resin was modified by sodium chloroacetate and the carboxyl groups were introduced. Its structure was characterized by Fourier transform-infrared spectra (FTIR) and scanning electron microscopy (SEM), respectively. The adsorption-desorption characteristics of the resin for Cu(II) in aqueous solution were investigated in detail using ICP-AES. The interaction between the metal ion and the resin was found to be depended upon the acidity of the medium. The prepared resin is strongly chelating and exhibits a chelating ability that can remove cupric ion in waste water treatment.

New quininium (Qn) plastic membrane electrodes of the conventional type were constructed and characterized. They are based on incorporation of Qn-reineckate (QnRn) ion-pair, Qn-phosphotungstate (Qn₃-PT), or Qn-phosphomolybdate (Qn₃PM) ion associate into a poly(vinyl chloride) membrane. The electrodes are selective for Qn and have been successfully used for the determination of Qn₂SO₄ in pharmaceutical tablets. Nevertheless, they showed, as almost all other ion-selective electrodes, limited life times. Energy dispersive- (EDS) and X-ray photoelectron spectroscopy (XPS), as well as electron microscopy were applied to investigate the cause of this limitation in the life times of the electrodes. The results indicated that the electrodes lose their activity after prolonged soaking as a result of leaching of the ion exchanger from the membranes into the test solution in addition to deformation at the surface of the expired electrode.

Aromatic compounds are extensively used in several industries and can cause pollution in water sources. This work aims at examining the degradability of aniline in aqueous solutions by ozone-induced cleavage, and at determining the kinetics of the cited cleavage reactions. Aniline was prepared in four different concentrations and the flow rate of ozone supplied to each solution was selected. Aniline solutions were ozonated at low and high pH, so as to compare both molecular and hydroxyl free radical mechanisms, respectively. The main identified aromatic by-products were nitrobenzene and azobenzene when the experiment was carried out at acidic pH. Formation of nitrobenzene, azobenzene, azoxybenzene and 2-pyridine carboxylic acid (picolinic acid) was observed when the ozonization was carried out at basic pH. All the aromatic by-products found were less toxic than the raw materials. The pseudo-first-order constants in aniline concentrations were calculated.

A method was established for the determination of trace impurities in high purity tellurium (Te) 99.9999 (6N) by radio frequency glow discharge optical emission spectrometry (RF-GDOES). The optimized parameters are power, argon pressure, pre-integration time, analysis time and selection of wavelength. Nine elements Se, Ca, Mg, Si, Fe, Cr, Cu, Ni and Pb were analysed in 6N Te, out of which only three elemental peaks (Se, Ca, and Mg) were detected and the remaining six elements (Si, Fe, Cr, Cu, Ni and Pb) were below detection levels. Finally, the method was evaluated by the analysis of the above traces using inductively coupled plasma mass spectrometry (ICP-MS) and was found to be satisfactory. The detection limits for most of the elements were below 10 ng/g and R.S.D. was around 10 %, which indicated that this method could fully satisfy the requirements for the trace analysis in high purity Te metal.

9-aminoacridine was firstly immobilized on the surface of a glassy carbon electrode to form a poly (9-aminoacridine) film modified electrode. The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of tyrosine and can resolve the interference of tryptophan in the determination of tyrosine. Compared with the bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. Under the optimum conditions, a linear response to tyrosine was observed in the concentration of 1.0×10^-6-2.8×10^-3 M, with a correlation coefficient of 0.9987, and a detection limit (S/N=3) of 1.0×10^-7 M. The modified electrode has been successfully applied to determine the concentration of tyrosine in composite amino acid injections; and it displays excellent repeatability and high sensitivity. The proposed sensor has promising features such as ease of fabrication, good reproducibility, high stability and low cost. And most of all, it has good selectivity.

An environmentally friendly and rapid digestion procedure involving 10 mL of acid mixture (HNO₃ : HCl : HF = 2:2:1) for 0.1 g of sample in closed vessel microwave digester following heating program : 250W for 10 min., hold time 2 min., 600 W for 17 min, and Ventilation time 10 min was developed. The operating parameters were varied and optimized by factorial design approach using “Steepest Ascent” method. The validity of the recommended digestion procedure were examined by analyzing several well characterized standard reference materials such as diabase (W2), basalt (BIR-1, JB-3, BHVO-1), granite (G2), gabbro (JGb-1), Mn-nodule (Nod-A-1, Nod-P-1), sediment (STSD-4, LKSD-2), limestone (KH-2), soil (SAu-1), ilmenite (IGS-31), rutile (IGS-32), Zircon (IGS-35) and titanium dioxide (SRM-154b) employing both inductively coupled plasma-atomic emission spectrometry (ICP-AES) and well known spectrophotometric method. An excellent agreement between the methods and the certified values of standard reference materials suggest that the digestion procedure can be used for quality control and allied purposes.