Mathematical modeling of cyclic voltammetry for EC<Subscript>2</Subscript> reaction

The non-steady-state concentration for an EC reaction at planar electrode is derived. The analytical expression for the concentration for EC reaction is reported for small and large value of reaction rate. The asymptotic expression for the non-steady-state current for EC reaction is also derived. The analytical solutions for normalized current response were formulated using the method of Laplace transformation. The concentration and current are compared with available limiting case results, and are found to be in good agreement.     

Mathematical modeling of cyclic voltammetry for EC reaction

The non-steady-state concentration for an EC reaction at planar electrode is derived. The analytical expression for the concentration for EC reaction is reported for small and large value of reaction rate. The asymptotic expression for the non-steady-state current for EC reaction is also derived. The analytical solutions for normalized current response were formulated using the method of Laplace transformation. The concentration and current are compared with available limiting case results, and are found to be in good agreement.     

高纯度树状大分子聚酰胺-胺的合成与表征

以乙二胺为核,通过Michael加成,与丙烯酸甲酯交替反应,合成了0.5代到5.0代聚酰胺 胺树状大分子。 利用傅里叶变换红外光谱、核磁共振氢谱、液相色谱和元素分析等对各代产品进行了表征,探索了反应温度、时间及反应物配比对产物的影响,确定生成聚酰胺-胺(PAMAM)的半代产物时反应温度为25 ℃,整代产物时反应温度为35 ℃;0.5G的反应时间为18 h,1.0G、1.5G的反应时间为24 h,2.0G、2.5G反应36 h,3.0G、3.5G反应48 h,4.0G、4.5G反应3 d,5.0G反应4 d。 分离提纯是树状大分子制备中遇到的最大困难,通过选择性溶剂萃取的方法对产品分离纯化,筛选出乙醚作萃取剂、甲醇作溶剂交换剂,大大提高了产品的纯度。     

Prediction of Retention in Liquid-Solid Chromatography with Ternary Mobile Phases

The method for the prediction of capacity factors in ternary mobile phases is presented. The adsorption mechanism of retention is considered. The simple theoretical equations are proposed for mobile phases for which the ratio of mole fractions of the weaker solvents remains fixed. The relations between parameters characterizing retention in ternary and binary mobile phases are discussed. The theoretical model is verified for numerous solutes and different mobile phases.     

Study of the determination of acetylcholine after enzymatic hydrolysis by triangle programmed coulometric flow titration

A new method for the determination of acetylcholine is introduced and studied. The method uses enzymatic hydrolysis of acetylcholine carried out in a flow-through analytical reactor column, while for the detection triangle programmed coulometric flow titration is employed. The flow-through coulometric titration system and the preparation of the enzyme reactor are described. The operation conditions for the hydrolysis and for the titration were optimized. The flow-through coulometric titration technique offers a better precision for the determination of acetylcholine in small concentration ranges than methods based on the detection of pH change. Working conditions of the system can be easily adjusted for different sample concentration ranges. The limit of detection for the determination of acetylcholine was found to be 8x10(-5) M. The method described could be advantageously used for indirect determination of acetylcholinesterase inhibitors.     

反相离子对液相色谱法测定欧洲鳗鲡体中丙硫咪唑及其代谢物的残留量

建立了鳗鲡体中丙硫咪唑及其代谢物残留量测定方法。样品用乙腈提取,经正己烷净化后,液相色谱一荧光法测定,标准加入法定量。流动相为：甲醇、乙腈和乙酸铵,梯度洗脱。检测波长为：激发波长290nm,发射波长320nm,丙硫咪唑、2氨基丙硫咪唑砜、丙硫咪唑亚砜、丙硫咪唑砜检出限依次为：25、5、10、1μg／kg。回收率大于95％,相对标准偏差小于8％。     

浅谈海洋环境监测质量保证工作的有效开展

总结近几年参与海洋环境监测质量保证工作的经验体会,对目前海洋环境监测质量保证工作中存在的主要问题进行了阐述,并就如何有效开展海洋环境监测质量保证工作提出建议。     

顶空固相微萃取-气相色谱-质谱联用分析纺织品中挥发性有机物

建立了顶空固相微萃取（HSSPME）-气相色谱（GC）-质谱（MS）联用测定纺织品中甲苯、4-乙烯基环己烯、苯乙烯、萘和1-苯基环己烯5种挥发性有机物（VOCs）的分析方法。选择聚二甲基硅氧烷（PDMS）作为萃取涂层,优化了SPME的萃取条件,包括平衡时间、萃取时间、萃取温度、顶空体积、离子强度、搅拌速度、解吸温度和时间以及GC—MS仪器条件。对于甲苯、4-乙烯基环己烯、苯乙烯、萘和1-苯基环己烯方法线性范围分别为0．087～870、3．32～3320、2．28～2280、0．015～150和0．050～50．0ng／g;检出限分别为0．005、0．042、0．670、0．008和0．011ng／g。实际样品加标回收率在80．1％～122％之间,RSD在0．8％～8．6％之间。方法符合纺织品中痕量VOCs的快速分析要求。     

Theoretical analysis of resonant raman scattering: Simulations of lineshapes and excitation profiles

The steady-state response of a three-level system in the presence of a strong laser field is described with the density operator formalism, in order to derive an analytical expression for the intensity of resonance Raman scattering. The Liouville equation for the density operator is written in quantum form for both the molecular system and the radiation field, making use of the dipole and rotating-wave approximations for the matter-radiation interaction, and of the Markov approximation for the molecular decays. The equation is solved exactly for the laser field, and in perturbative way for the generated field. The results account for power broadening of the generated line. Rabi intensity-dip of the generated signal, and for the excitation profiles in the Franck-Condom approximation.     

Utilisation of polypyrrole modified electrode for the determination of pesticides

Cyclic voltammetric studies of isoproturon and carbendazim using polypyrrole modified glassy carbon electrode were carried out. The electrode and reaction conditions, which yielded maximum current signal, were selected for the development of stripping voltammetric procedure for the determination of the pesticides. The oxidation peak around 1.3?V obtained for isoproturon and carbendazim while employing polypyrrole modified electrode showed maximum current response. This peak was chosen for stripping analysis using square wave mode. The experimental parameters were optimized and the calibration plot was obtained. The LOD was 0.5?ng?mL^?1 for isoproturon and 5?ng?mL^?1 for carbendazim. The relative standard deviation for 5 identical measurements was 2.81% and 3.33% for isoproturon and carbendazim respectively. The applicability of the method was verified by determining the pesticides in spiked soil and water samples.     

Determination of enrofloxacin and its metabolite ciprofloxacin in goat milk by high-performance liquid chromatography with diode-array detection. Optimization and validation

A high-performance liquid chromatography-diode array detection method (HPLC-DAD) combined with liquid chromatography-mass spectrometry was developed for the determination of enrofloxacin and its metabolite ciprofloxacin in goat milk. The HPLC-DAD method validation was compliant with the "DG SANCO 1805/2000" European regulation. The residues were extracted from milk with phosphate buffer, purified on a C18 Speedisk cartridge SPE (Baker) and then analysed using HPLC-DAD set at 277 nm. The decision limit (CCa) calculated by spiking samples at 100 microg/kg with both analytes, taking into account the maximum residue limit (MRL) of 100 microg/kg established by the European Union for the sum of enrofloxacin and its metabolite ciprofloxacin in milk, was 105.3 microg/kg for enrofloxacin and 105.5 microg/kg for ciprofloxacin. The detection capability (CCbeta) was 110.7 and 110.9 microg/kg for enrofloxacin and ciprofloxacin, respectively. The mean recoveries of the method, calculated by spiking samples at 50, 100 and 150 microg/kg were 84% for enrofloxacin and 88% for ciprofloxacin. The limit of quantification was 20 microg/kg for both analytes. The HPLC-DAD validated method was successfully applied for the first time in goats milk, and proved to be suitable for the sensitive and accurate quantification and confirmation analysis of enrofloxacin and ciprofloxacin for regulatory purposes.     

An improved iodometric method for the successive determination of copper and zinc

The method described by haider and khundkar for the succesive iodometric dctcrmination of copper and zinc gives results that arc too low both for copper and for zinc. The errors may amount to —20% for copper and to —5% for zinc. The causes of these errors arc traced and eliminated and an improved method for the succesive iodometric determination of copper and zinc is described.     

3D-map modelling for the melting points prediction of intumescent flame-retardant coatings

The applicability of 3D map modelling for melting point prediction was studied. The melting points in the ammonium polyphosphate–pentaerythritol–melamine chemical system of intumescent flame-retardant coatings over a wide range of concentrations were collected. The ternary diagram (triangle) of the melting points was plotted and an approximated 3D map was built for the range 205–345°C. The present work contains the thermal data for the observed ternary system and provides a new graphic system for making predictions for intumescent flame-retardant coatings. The applicability of the calculated 3D map for obtaining experimental samples of fire-retardant paints with a low melting point for thin steel constructions was shown.     

High performance liquid chromatographic determination of theophylline metabolites in human liver microsomes

A high performance liquid chromatographic (HPLC) technique for the determination of three metabolites of theophylline, 3-methylxanthine (3-MX), 1-methylxanthine (1-MX) and 1,3-dimethyluric acid (1,3-DMU) in human liver microsomes is described. The analytes were extracted from human liver microsomes with methylene chloride/isopropanol and stepwise gradient elution was employed for the resolution of peaks. The limits of quantitation were 15 ng/mL for 3-MX, 20 ng/mL for 1-MX and 20 ng/mL for 1,3-DMU. The calibration range was linear for the three metabolites and the calibration ranges were 15-250 ng/mL for 3-MX, 20-250 ng/mL for 1-MX and 250-4000 ng/mL for 1,3-DMU. The absolute recovery ranged from 63-84% for 3-MX, 65-79% for 1-MX and 77-89% for 1,3-DMU over the calibration curve range. Accuracy for all three metabolites was within +/- 10% and adequate selectivity was demonstrated by the lack of interfering peaks in blank chromatograms. The within-run and interday precision were within 10% RSD for all three metabolites tested at two concentrations. The advantage of this method over previous methods is that the use of quaternary ammonium ion pair reagents in the mobile phase has been obviated. Also, unlike a previous radiometric HPLC method, the need for radiolabelled theophylline has also been eliminated. The method was used to characterize theophylline metabolism in human liver microsomes for immunoinhibition studies and to investigate the interaction of theophylline with selected quinolone antibiotics.     

Electronic structures of the ground state and excited singlet states of nucleic acid bases

The self-consistent field (SCF) method is used in the semiempirical approximation (SA) with allowance for singly excited configurations to derive the ground state and singlet excited states for five nucleic acid bases (NAB). Empirical values are used for the nondiagonal elements of the matrix for the two-electron Coulomb integrals. The methyl group in thymine is allowed for via an induction model. Theoretical values are given for the energies of the first four electronic transitions for each base. The locations of these agree well with spectroscopic data. The energies of the first two transitions in adenine are found to be very similar when allowance is made for configuration interaction, so the first absorption band of adenine arises from overlap of two transitions.     

Simple high-performance liquid chromatographic method for determination of atropine and obidoxime in a parenteral injection device

Atropine and obidoxime in a parenteral injection device are determined by simple HPLC method simultaneously without any pretreatment at 228 nm. The relative standard deviations (R.S.D.) were below 1.6% for the compounds. The correlation coefficient was greater than 0.999 for both compounds in the calibration range. The recoveries at 5 mg/L concentration averaged as 95% for atropine and 102% for obidoxime. The uncertainty of the measurements for atropine and obidoxime was 2.8% and 2.4%, respectively.     

饮用水中氯酸盐、亚氯酸盐的离子色谱测定方法

建立了饮用水中微量氯酸盐以及亚氯酸盐的离子色谱测定方法。结果表明,亚氯酸盐和氯酸盐在0～0.50 mg/L范围内线性良好,精密度高,亚氯酸盐r2=0.999 8,样品加标平均回收率91.5%～99.4%,相对标准偏差(RSD)0.64%～1.78%,检出限为3.98μg/L;氯酸盐r2=0.999 6,样品加标平均回收率94.7%～101.6%,相对标准偏差(RSD)0.94%～1.35%,检出限为4.65μg/L;方法操作简单、快速、准确、灵敏度高、干扰少,适用于饮水消毒副产物亚氯酸盐和氯酸盐的检测。     

MOCASSIN: Metropolis and kinetic Monte Carlo for solid electrolytes

The combination of density functional theory and Monte Carlo simulations is a powerful approach for the atomistic modeling of defect transport in solid electrolytes. The present contribution introduces the MOCASSIN software (Monte Carlo for Solid State Ionics) for kinetic and Metropolis Monte Carlo simulations of crystalline materials. MOCASSIN combines model building, visualization, and simulation, aiming to provide accessible MC for end users. Developed for the investigation of solid electrolytes, MOCASSIN is ideal for screening common variation parameters, such as temperature and doping fraction. The input effort is minimized using space groups for processing symmetry. The graphical interface for model building allows complex model input, including multiple mobile species, multiple migration paths, small polaron hopping, vehicle movements, multiple complex migration mechanisms, and custom interaction clusters. The software is provided free of charge for noncommercial usage.     

Miniaturized automated matrix solid-phase dispersion extraction of pesticides in fruit followed by gas chromatographic-mass spectrometric analysis

In this study a simple and fast miniaturized automated matrix solid-phase dispersion method for the sample preparation and quantitative extraction of pesticides was developed and evaluated. Only 25 mg of sample and 100 microl of organic solvent were used per analysis for this new miniaturized set-up. The extracts were subsequently analysed by GC-MS without any further purification. The method was optimized for oranges and tested for the determination of a variety of organophosphorus pesticides and a pyrethroid at concentration levels below the maximum residue levels set by the European Union and authorities in The Netherlands. The limits of detection were 4-90 microg/kg. The recoveries for pesticides in orange were 83-118% and the relative standard deviations for the total procedure were 10-13% (n=4) at the limit of quantification. The feasibility of the developed method for apple, pear and grapes was also studied. Equally good results were obtained, but for apple the washing step should be omitted.     

The method of moments for multiplet deconvolution in gamma-ray spectrometry

The method of moments is described for deconvolution of a mixture of identical distributions; it is not necessary to know the type of the individual peak distribution. The algorithm for computing the positions and contributions of the peaks forming the multiplet is presented. The real shape of the peak is used. The computational stability of the method of moments for the deconvolution of various types of convolved triple peaks is shown to be satisfactory. The algorithm is used for deconvolution of some double peaks obtained in neutron activation analysis of rock standards. The program is fast and suitable for microcomputers.