Fluorimetric determination of ascorbic acid with o-phenylenediamine

A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) is described. The method is based on the condensation reaction between AA and o-phenylenediamine (OPDA) in the absence of the oxidant. The fluorescence intensity is measured at excitation and emission wavelengths of 360 and 430 nm, respectively. Under optimum condition, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range of 0.05-40 μg ml⁻¹. The detection limit is 0.006 μg ml⁻¹, which is obviously lower than that of other fluorimetric methods reported.     

Identification of a chemical indicator of the rupture of 1,4-β-glycosidic bonds of cellulose in an oil-impregnated insulating paper system

In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by the ageing of oil-impregnated paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative conditions 0.5-g specimens of insulating paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of paper (ordinary Kraft or thermally-upgraded (TU) Kraft paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft paper constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the system. Furthermore, additional 130 °C-tests with six different papers and pressboard samples under a tight control of initial moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and TU-nitrogenous agents modify the methanol partitioning coefficients in the paper/oil/air system, which makes their study essential over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with 2-furfuraldehyde, which is the current reference in the domain.     

Organic–inorganic nanocomposites prepared from fluoro-aramid and silica

Fluoro-aramid-based sol/gel-derived nanocomposites were synthesized by condensing a mixture of 4,4′-(hexafluoro-isopropylidene)dianiline and 1,3-phenylenediamine with terephthaloylchloride (TPC) in dimethylacetamide. TPC was added in slight excess to produce amide chains with carbonyl chloride end groups and then replaced with alkoxy groups using aminophenyltrimethoxysilane to develop bonding with the silica network. Mechanical, dynamic mechanical thermal, water absorption and morphological measurements were carried out on the thin hybrid films. Increase in the tensile strength and modulus was observed as compared to pristine polyamide. The thermal decomposition temperature was found in the range of 400–500 °C. The water absorption was found to be reduced with higher silica content. The glass transition temperature and the storage moduli increased with increasing silica concentration. The maximum increase in the T _g value (345 °C) was observed with 20 wt% silica. Scanning electron microscopy revealed the uniform distribution of silica in the matrix with an average particle size ranging from 8 to 50 nm.     

HPLC–MS Analysis of Isoniazid in Dog Plasma

A simple, rapid, and sensitive liquid chromatography–mass spectrometric (LC–MS) method was developed and validated for the determination of isoniazid in dog plasma. Plasma samples were deproteined with methanol and separated on a C₁₈ column interfaced with a single quadrupole mass spectrometer, using 0.1% formic acid–acetonitrile (91:9 v/v) as mobile phase. Detection was performed by positive electrospray ionization with selected ion monitoring at m/z 138 for isoniazid and 152 for entecavir maleate internal standard. Linearity was obtained over the range of 25–5,000 ng mL^?1, with a lower limit of quantification of 25 ng mL^?1. The intra- and inter-day precision was less than 2.7% in terms of relative standard deviation. Accuracy, expressed as relative error, ranged from ?2.0 to 8.0%. Plasma samples were analysed within 5 min. The method was successfully applied to the evaluation of the pharmacokinetics of isoniazid in dog plasma.     

吲哚乙酸与磷钼黄反应及其极谱分析的研究

在ＮＨ３－ＮＨ４Ｃｌ缓冲溶液中（ｐＨ＝９．５），吲哚乙酸与磷钼黄的还原产物在滴汞电极上于－１．１０Ｖ（ｖｓ．ＳＣＥ）处产生一灵敏的极谱波，该波波高与吲哚乙酸的浓度在１．０×１０－７－５．０×１０－６ｍｏｌ／Ｌ范围内成线性关系，检测下限为５．０×１０－８ｍｏｌ／Ｌ。如在上述还原产物中加入偶氮胭脂红Ｂ、孔雀绿、甲基紫等染料及聚乙烯醇，可使极谱波的灵敏度提高，使吲哚乙酸的浓度在５．０×１０－８－１．０×１０－６ｍｏｌ／Ｌ范围内与波高成线性关系，检测下限降低至１．０×１０－８ｍｏｌ／Ｌ。     

Na_6V_（10）O_（28）·12H_2O的合成与结构

合成并测定了十钒酸盐Ｎａ_６Ｖ_（１０）Ｏ_（２８）·１２Ｈ_２Ｏ的单晶结构。晶体属单斜晶系，Ｐ２_１／ｎ群空间，ａ＝１２．０１９（２），ｂ＝１７．１５４（２），ｃ＝１８．１７８（６），β＝１０６．２９（２）°，Ｖ＝３５７９（１），Ｍ_ｒ＝１２８７．５，Ｆ（０００）＝２５６０，μ＝２５，４４ｃｍ￣（－１），Ｚ＝４，Ｄ_ｃ＝２．３８ｇ·ｃｍ（－３）。结构由重原子法解出，全矩阵最小二乘法修正至Ｒ＝０．０６４，Ｒ_ｗ＝０．０８３。Ｖ_（１０）簇阴离子可以看成由１０个ＶＯ_６变形八面体形成，其中氧原子有４种类型：端氧、二桥氧、三桥氧和六桥氧。结果表明，阳离子相同但结晶水的数目不同时，十钒酸盐的晶系和空间群不同。     

几种双核簇合物的EPR谱

本文报导了四个双铜,四个双钼簇合物的EPR谱。这些谱可分成两类:一种类似于单核化合物的EPR谱,谱参数与单核谱相近,但谱强度较单核谱弱,文中称之为“碎片型”;另一类的谱参数与双核偶合的体系相同,谱的强度与双核偶合程度有关、反映双核偶合成簇的性质,称之为“簇型”。两类谱受温度和溶剂的影响分别呈现正常与反常的顺磁性。本文对它们与簇合物结构-性质间的关系作了初步探讨。     

Mössbauer study on surface magnetic properties in magnetic fluids

The presence of m=0 lines of the Mössbauer spectra of small Fe₃O₄ particles coated with an organic surfactant in an applied field of 7 T at 5 K shows a non-collinear magnetic structure in the surface layer of these particles. From the temperature dependence of the hyperfine field, the anisotropy constantK was calculated.Projects supported by the Science Fund of the Chinese Academy of SciencesNow working at the Shanghai Institute of Education     

Excited states in126Ba

The K=3/2 ₁ ^T rotational band has been identified in⁹⁹Y with a band-head energy of 536 keV. This result is in contradiction with previously reported data, but is in agreement with predictions of the IBFM/PTQM model.