Si-tolerance of iron doped Pt/alumina catalyst in the total oxidation of VOC

Summary In the present study the effects of addition of iron on the catalytic activity and Si tolerability of Pt/g-Al₂O₃in the total oxidation of volatile organic compounds were investigated. Preliminary results showed that there is a noticeable improvement effect on Si-tolerance of catalyst, particularly for short term poison exposure. Bulk analysis of deposited silicon on the catalyst surface indicated that both Pt/g-Al₂O₃and iron-doped pellets had roughly the same silicone uptakes. Deactivation of catalyst was reversible and much faster for iron doped sample. The promoting effects of iron were related to its electronegativity and, to blocking of fewer Pt sites when iron is present at the surface of the catalyst.     

二乙基二硫代氨甲酸银体系流动注射法测定砷

本文设计了一种ＡｇＤＤＣ流动注射－分光光度法测定砷的系统。该系统采用自制的氢化物发生及吸装置，将液体流路和载气流路结合在一起。     

流动注射分光光度法测定水体总磷

提出了一种单通道紫外消解流动注射比色分析法，能快速测定水样中总磷。实验采用了微量恒流混合泵、新型的细长型高灵敏度流通池及紫外消解器、液流分配阀、恒流瓶等FIA装置，并使用工业编程控制器和智能触摸屏进行控制和计算，使操作更为方便。此法分析时间短，测量范围宽，精度高，适合于各种水体的测定。     

Kinetic determination of trace levels of selenium(IV) and total selenium by Nile Blue A/hydrogen peroxide method

A kinetic method for the determination of selenium(IV) traces is proposed, based on its inhibitory action on the oxidation of Nile Blue A by hydrogen peroxide in phosphate buffer (pH 10.5). A linear dependence was established between the rate of the proposed indicator reaction and selenium concentration in the range 9.5 × 10^–2-1.58 ng cm^–3. The experimental conditions of maximal selenium effect were established. Selenium, determined by the tangent method, was determined at concentrations over the range 0.22–1.26 ng cm^–3, with relative standard deviations up to 4.5%. The reaction rate was followed spectrophotometrically. The effect of foreign ions on the accuracy of this method was also investigated. The method was applied to the determination of selenium in pharmaceutical preparations and wheat flour.     

Synthesis of jasplakinolide analogues containing a novel omega-amino acid

The synthesis of the omega-amino acid 4 is described utilizing a two-dimensional synthesis strategy combined with an enzymatic differentiation of homotopic ester groups. The amino acid 4 features two non-bonded interactions that result in conformational constraints on a cyclic construct. This amino acid was incorporated into the four macrolactams 17, 22, 31, and 37. The ring in 17 and 22 is 18-membered, whereas 31 and 37 have a 19-membered ring. The pairs with the same ring size differ in a N-methyl group. For the larger macrolactams (31 and 37) conformational analysis showed that the macrocyclic rings are somewhat more rigid than in the natural lead, the depsipeptide jasplakinolide. Nevertheless, their conformations are comparable to the natural product. There are no intramolecular hydrogen bonds, neither is the cis-rotamer populated in the N-methyl compound 37. Due to the increased flexibility of the smaller macrolactams 17 and 22 and signal overlap, a distinct solution structure could not be obtained for these compounds. The amino acid 4 should be useful for restricting the conformation of other small peptides.     

Temperature and humidity aging of poly(p-phenylene-2,6-benzobisoxazole) fibers: Chemical and physical characterization

In recent years, poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers have become prominent in high strength applications such as body armor, ropes and cables, and recreational equipment. The objectives of this study were to expose woven PBO body armor panels to elevated temperature and moisture, and to analyze the chemical, morphological and mechanical changes in PBO yarns extracted from the panels. A 30% decrease in yarn tensile strength, which was correlated to changes in the infrared peak absorbance of key functional groups in the PBO structure, was observed during the 26 week elevated temperature/elevated moisture aging period. Substantial changes in chemical structure were observed via infrared spectroscopy, as well as changes in polymer morphology using microscopy and neutron scattering. When the panels were removed to an ultra-dry environment for storage for 47 weeks, no further decreases in tensile strength degradation were observed. In a follow-on study, fibers were sealed in argon-filled glass tubes and exposed to elevated temperature; less than a 4% decrease in tensile strength was observed after 30 weeks, demonstrating that moisture is a key factor in the degradation of these fibers.     

Synthesis and inhibitory activity of alkyl(hydroxyaryl)amines

The reaction of ω-(4-hydroxyaryl)haloalkanes with various nitrogen-containing agents afforded primary, secondary, and tertiary amino derivatives of 2,6-dialkylphenols. For the compounds synthesized, the reaction rate constants with peroxide radicals were measured for cumene and methyl oleate oxidation. The total inhibitory activity in the model reactions of thermal autooxidation of lard and hexadecane was studied. The rate constants of alkyl(hydroxylaryl)amines are the same as those of the corresponding alkylphenols, whereas the total inhibitory activity of some alkyl(hydroxylaryl)amines exceeds substantially that for alkylphenols. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1107–1112, June, 2007.     

Studies of surface properties of Na- and La-montmorillonites

This paper presents possible applications of thermal analysis, sorptometry and porosimetry to study physico-chemical properties of Na- and La-montmorillonite samples, especially for determination of total surface heterogeneity. The quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative (Q-DTG) curves with respect to temperature and time obtained during programmed liquid thermodesorption under quasi-isothermal conditions have been used to study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites. Calculations of the desorption energy distribution functions by analytical procedure using mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption under quasi-isothermal conditions of polar and non-polar liquid vapours preadsorbed on a material surface are presented. Parameters relating to porosity of samples were determined by sorptometry, mercury porosimetry and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry and porosimetry methods, the fractal dimensions of montmorillonites have been calculated. Moreover, a new approach is proposed to calculate fractal dimensions of materials obtained from Q-TG curve; this is compared with values obtained by the above methods. The total heterogeneous properties (energy distribution function and pore-size distribution functions) of samples studied were estimated. The radius and pore volume of the tested samples calculated on the basis of thermogravimetry, sorptometry and porosimetry techniques were compared and good correlations obtained.     

Determination of arsenic in mussels by slurry sampling and electrothermal atomic absorption spectrometry (ETAAS)

A method for the determination of arsenic in slurries of mussel tissue using palladium-magnesium nitrate as modifier was optimized. The slurry was stabilized by a 0.015% (v/v) of Triton X-100. To achieve complete mineralization the slurries were ashed at 480 °C for 10s in an air flow (50 ml/min) and at 1200 °C for 15s in an argon flow (300 ml/min) in the presence of Pd—Mg(NO₃)₂ as modifier. The optimum atomization temperature was 2200 °C. The precision and accuracy of the method were studied using the Reference Material BCR n ° 278 Mussel Tissue (Mytilus edulis). The detection limit (LOD) of the final slurry solution was 1 g/l of arsenic corresponding to an arsenic level in the mussel of 1.3 g/g, for a 0.5% (m/v) slurry. Results of calibration using aqueous standards and the standard additions method were compared. The method was applied to the determination of arsenic in mussels from the Galician coast. The levels found lie between 2 and 9.3 g/g of arsenic.     

Optimization of a GFAAS method for determination of total inorganic arsenic in drinking water

The new 10 μg l⁻¹ arsenic standard in drinking water has been a spur to the search for reliable routine analytical methods with a limit of detection at the μg l⁻¹ level. These methods also need to be easy to handle due to the routine analyses that are required in drinking water monitoring. Graphite furnace atomic absorption spectrometry (GFAAS) meets these requirements, but the limit of detection is generally too high except for methods using a pre-concentration or separation step. The use of a high-intensity boosted discharge hollow-cathode lamp decreases the baseline noise level and therefore allows a lower limit of detection. The temperature program, chemical matrix modifier and thermal stabilizer additives were optimized for total inorganic arsenic determination with GFAAS, without preliminary treatment. The optimal furnace program was validated with a proprietary software. The limit of detection was 0.26 μg As l⁻¹ for a sample volume of 16 μl corresponding to 4.2 pg As. This attractive technique is rapid as 20 samples can be analysed per hour. This method was validated with arsenic reference solutions. Its applicability was verified with artificial and natural groundwaters. Recoveries from 91 to 105% with relative standard deviation <5% can be easily achieved. The effect of interfering anions and cations commonly found in groundwater was studied. Only phosphates and silicates (respectively at 4 and 20 mg l⁻¹) lead to significant interferences in the determination of total inorganic arsenic at 4 μg l⁻¹.