High-order one-step P-stable methods for the numerical integration of periodic initial value problems

Using Lobatto nodes, one-step methods of order six and eight have been obtained for the second-order differential equation y″ = f(x, y), y(x₀) = y₀, y′(x₀) = y′₀. The methods are shown to be P-stable. If

, then at each integration step a system of dimension 3s, 4s, respectively, has to be solved. The numerical results, for two problems, obtained by using these methods are given in the end.     

Determination of bromine in organic compounds by high-performance liquid chromatography

A method is proposed for the determination of bromine in organic compounds (which may also contain chlorine and iodine) by oxygen-flask combustion of the compound followed by pre-column reaction of bromide with acetanilide and 2-iodosobenzoic acid to form 4-bromoacetanilide which is then chromatographed on an ODS column with a mobile phase of methanol: water, 65:35 v/v, detection at 240 nm, and 4-N-acetylaminotoluene as internal standard. The method is rapid and precise (RSD 相似文献   

Investigation of Pd leaching from supported Pd catalysts during the Heck reaction

Palladium supported on amorphous silica, mercapto-functionalized silica, amine functionalized silica, and zeolite Y has been studied as a catalyst in the Heck reaction of iodobenzene with butyl acrylate in the presence of triethylamine base and dimethylformamide solvent. Trapping of soluble Pd with poly(4-vinylpyridine), hot filtration tests during the batchwise Heck reaction, and reaction tests of effluents from a fixed bed continuous reactor support the conclusion that leached Pd is the active phase in the Heck reaction for all of the catalysts tested. Two different paths of Pd leaching that depend on the chemical state of the Pd were elucidated in this study. Oxidative addition of aryl halide to reduced Pd caused leaching of samples containing metallic particles. However, for a zeolite Y sample containing unreduced cationic Pd, the presence of triethylamine base was required to leach Pd into solution. These two paths of Pd leaching are consistent with the generally accepted mechanism of the Heck reaction.     

Spectrophotometric determination of ruthenium(III) and iridium(TV) with 8-hydroxyquinoIine N-oxide

The spectrophotometric characteristics and the stability constants of the yellow to brown 1:1 and 1:2 complexes of platinum metals with oxine N-oxide (existing as chloro mixed-ligand complexes) have been investigated. Oxine N-oxide can be used as a spectrophotometric reagent for ruthenium(III) and iridium(IV).     

Determination of isotopic composition of boron

Investigations were carried out on the determination of isotopic composition of boron using Cs₂BO ₂ ⁺ ion and thermal ionisation mass spectrometry. The results show distinct advantage over the normally used Na₂BO ₂ ⁺ ion.     

Determination of H2 and D2 content in metals and alloys using hot vacuum extraction

A hot vacuum extraction technique for the determination of hydrogen in metal and alloy samples has been standardised. After measuring the total pressure of the evolved gases, individual hydrogen and deuterium intensities are measured using an on-line quadrupole mass spectrometer. Synthetic mixtures of H₂ and D₂, in known concentrations, have been analysed by QMS and an analytical expression correlating the measured [D₂]/[HD] intensity ratio with the mole fraction of deuterium in the synthetic mixture has been arrived at. The precision and accuracy in the measurement of hydrogen is about 10% at 50 ppmw level.     

Spectrophotometric determination of ascorbic acid in pharmaceuticals by background correction and flow injection

Background correction has been shown to be an effective and indispensable modification in the spectrophotometric determination of ascorbic acid. The decomposition of ascorbic acid in pharmaceutical samples was carried out by incubation with sodium hydroxide to give products that were insensitive to ultraviolet light. The rapid oxidation in air of ascorbic acid, especially in dilute solutions, was avoided by the use of the flow injection principle for spectrophotometric determination and by employing a carrier stream of an anti-oxidizing nature consisting of 6 micrograms ml(-1) of 2-mercaptoethanol in 0.25% sulphuric acid. The optimized method with a single channel manifold made use of a carrier stream flow rate of 1.1 ml min(-1), an injection volume of 50 microl, a delay coil of 50 cm (0.5 mm i.d.) and detection at 245 nm. The throughput was at least 180 injections h(-1). The proposed flow injection method yielded results for the analysis of 0-20 micrograms ml(-1) of ascorbic acid that were 99-102% (relative standard deviation 0.6% or better) in agreement with those produced by comparable methods involving titration with iodine, chloranil or 2,6-dichlorophenolindophenol [4-(2,6-dichloro-4-hydroxyphenylimino)cyclohexa-2,5-dieno ne], and high-performance liquid chromatography. When the agreement was not good (as low as 14% with respect to the method being compared), this was traced to the presence of substances which are known to interfere in one or other of the methods of comparison.     

Effect of Phosphorus Content on Thermal Behaviour of Diglycidyl Ether of Bisphenol-A/phosphorus Containing Amines

Curing of diglycidyl ether of bisphenol-A (DGEBA) with phosphorus containing amide amines i.e. bis[3(3’-aminobenzamido phenyl)]methyl phosphine oxide (MB),bis[3(4’-aminobenzamido phenyl)]methyl phosphine oxide (PB), tris[3(3’-aminobenzamidophenyl)] phosphine oxide (MT) and tris[3(4’-aminobenzamido phenyl)] phosphine oxide (PT)and conventionally used curing agent 4,4’-diaminodiphenyl sulfone (D) was studied by DSC. The amines MB, PB, MT and PT were synthesised in the laboratory and were characterized by determining elemental composition, melting point, and amine equivalent. Structural characterization was done by ¹H-NMR and FTIR. The onset temperature of curing depended on the nucleophilicity of the amines and was in the orderMT≈MB<PT<PB<D. The exothermic peak temperatures were in the orderD>PB>PT>MT≈MB. The char residue of cured epoxy resin was significantly higher when phosphorus was incorporated in the cured network. Using mixed amine formulations based on amine D and P-containing amines and the molar ratio of these amines could easily control the curing characteristics. A linear relationship between char yield and P-content was observed in such formulations. This revised version was published online in August 2006 with corrections to the Cover Date.     

HPLC Determination and Pharmacokinetic Study of Valdecoxib in Human Plasma

A sensitive, simple, and accurate high-performance liquid chromatographic method has been developed for determination of valdecoxib and the internal standard rofecoxib in human plasma. Protein was precipitated from plasma samples by addition of perchloric acid (HClO₄); the drug was then extracted with diethyl ether. Separation was performed on a Cosmosil C₁₈ column (150 mm × 4.6 mm i.d., 5 m particles) with ammonium acetate buffer-acetonitrile, 60:40 (v/v), containing 0.1% TEA, pH 6.5, as mobile phase. Detection and quantification were performed by UV-visible detection at 239 nm. Detection and quantification limits were 3 and 5 ng mL^–1, respectively. The linear concentration range for valdecoxib was 5–400 ng mL^–1. The validated RP HPLC method was used for determination of the pharmacokinetic data for the drug in humans.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.