对络合返滴定过程的理论探讨

推导了络合返滴定曲线方程 ,绘制了络合返滴定曲线和计算了pN突跃。并利用双曲正弦函数的性质 ,提出了内含最大敏锐指数的络合返滴定误差计算公式 ,从而获得了计算络合返滴定pN突跃范围的公式。     

酸碱滴定：滴定剂液滴尺寸与滴定突跃

存在滴定突跃是滴定分析可以进行的先决条件。国内教科书讨论突跃范围的概念时均利用了滴定分数100±0.1%的条件,即按照滴定分数99.9%和100.1%来计算突跃范围。实际上,滴定过程中滴定剂是以液滴为单位加入到被测溶液中的,指示剂滴定法中也是以一滴或半滴标准溶液加入后被测溶液颜色发生改变来确定终点的,因此,按照化学计量点前后欠缺或过量半滴标准溶液来计算突跃范围更具科学性和实用价值。本文将计量点附近单滴滴定剂加入被测溶液引起的p H变化定义为突跃范围。对强碱滴定一元强酸体系的突跃范围进行了数学计算。结果表明,突跃范围与被测溶液的体积和浓度、滴定剂的浓度和液滴尺寸、被测溶液和滴定剂的浓度比等因素都有密切相关性,给出了不同于教科书的某些重要结论,这些新结论与实际滴定情形相符,对指导滴定分析具有重要参考价值。     

强碱滴定一元弱酸突跃范围的计算

针对现有教材及文献对弱酸滴定计量点附近某些不甚合理的简化处理过程以及某些值得商榷的结论,根据滴定弱酸计量点附近溶液的实际组成,推导了合理的、适用任何情况的强碱滴定一元弱酸的突跃范围计算公式,从而给出了一元弱酸被准确滴定的判据。     

用滴定突跃的绝对值推导四大滴定分析的直接准确滴定条件

建立了四大滴定分析"滴定突跃绝对值"的概念;用滴定突跃绝对值推导出四大滴定分析直接准确滴定的条件。     

混合离子的沉淀准确滴定

用沉淀滴定的林邦滴定曲线方程推导滴定突跃的绝对值,用滴定突跃的绝对值推导混合离子准确滴定的条件。     

络合滴定中的滴定误差

利用双曲正弦函数的性质,提出了一种处理络合滴定误差的新方法,导出了一个内含最大敏锐指数的络合滴定误差公式,进而获得了计算络合滴定突跃范围的公式。其处理结果与传统方法一致。     

氧化还原滴定终点误差

借助导数及双曲正弦函数性质建立了一种处理两电对均为对称电对的氧化还原滴定终点误差的新方法。导出了包含敏锐指数的氧化还原滴定终点误差公式。据此讨论了滴定突跃范围及滴定可行性问题。     

多元弱酸的准确滴定

用二元弱酸滴定的林邦滴定曲线方程推导第一和第二滴定突跃绝对值,用第一和第二滴定突跃绝对值推导二元弱酸第一和第二级解离的H+准确滴定的条件,并将其应用于多元弱酸的准确滴定.     

氧化还原滴定中计算等当点电位及其在突跃线上的位置的讨论

在氧化还原滴定中,若两个半反应得失电子数相等(即n1=n2),则滴定曲线突跃部分在等当点前后是对称的,即滴定的等当点位于突跃曲线的中点。反之,若两个半反应的得失电子数不相等(即n1≠n2),则滴定曲线的突跃部分在等当点前后是不对称的。     

氧化还原滴定的理论公式

本文提出了氧化还原滴定理论处理的一般模型，导出了化学计量点电位计算通式和终点误差的计算通式，给出了滴定突跃范围及指定误差要求时终点电位允许变动范围的一般计算方法。本处理方法推导过程严谨、系统而简明，优于现有文献及专著的报道。     

临界点二级相变的有限时间热力学逼近

应用内可逆卡诺循环的方法,导出了各种物质在临界点附近可逆与不可逆二级相变普遍适用的比热跃变公式以及广义的爱伦菲斯特方程。对简单(P,V,T)系统、超导、电介质顺电一铁电二级相变进行了应用讨论。     

Diffusion of particles over dynamically disordered lattice

Using kinetic Monte Carlo simulations we have investigated the diffusion of particles over a lattice with moving atoms in the framework of a simple lattice-gas model of a reconstructive surface. The particle migration over the static and dynamic lattices differs considerably. The dynamic lattice reconstruction changes substantially the particle diffusion coefficient. The Arrhenius dependencies are quantitatively different. An interesting peculiarity of the particle migration is the formation of defectons--local lattice deformations around the adsorbed particles. In certain ranges of the system parameters (jump rates of the substrate atoms and adsorbed particles) the adsorbed particles cause local displacements of the nearest substrate atoms, resulting in deeper adsorption sites and lower jump rates. Such particle self-trapping produces a characteristic minimum on the Arrhenius dependencies.     

Analytical probability distribution function for a one-dimensional anharmonic oscillator in thermal equilibrium

A simple closed formula is proposed for the probability distribution function of a one-dimensional anharmonic oscillator in thermal equilibrium. It is shown that this formula yields a plausible approximation for the distribution function over wide ranges of the parameter θ = hcωelkT and the degree of anharmonicity. A more general formula with extended limits of applicability is also considered.     

低级直链醇分子横截面积测定实验的改进研究*

为提高教学实验低级直链醇分子横截面积测定结果的准确性,本研究通过最大气泡法,以Szyszkowski公式为拟合方程,在所设定的4个浓度区间内对各种低级直链醇的分子横截面积进行系统化研究,从而确定了不同醇适用该法的大致浓度区间,同时讨论了直链醇碳链长度、浓度与醇分子表面吸附行为3者之间的内在联系。     

FORSTER TRANSFER RATES FOR CHLOROPHYLL a*

Abstract— A convenient formula has been derived for the calculation of Forster transfer rates between chlorophyll a molecules. The formula is applicable over limited ranges of absorption maxima positions, Stokes' shifts, solvents, relative orientations and intermolecular distances. The limitations on the applicability of the Forster transfer model are discussed. Finally, some implications for in vivo energy transfer are considered.     

Liquid chromatographic analysis of vitamin B6 in reconstituted infant formula: collaborative study

A liquid chromatographic (LC) method was validated for the determination of total vitamin B6 in infant formula. Total vitamin B6 was quantified by converting the phosphorylated and free vitamers into pyridoxine. Pyridoxine was determined by ion pair reversed-phase LC with fluorescence detection. The method was subjected to an AOAC collaborative study involving a factory-manufactured, milk- and soy-based infant formula. Each was spiked at 3 concentrations in the range of 0-1 microg/g and sent as blind duplicate to participant laboratories. Nine laboratories returned valid data which were statistically analyzed for outliers and precision parameters. The repeatability relative standard deviation (RSD(r)) ranges were 2.0-4.0 and 3.5-5.9% for fortified milk- and soy-based formulas, respectively. The reproducibility relative standard deviation (RSD(R)) ranges were 8.2-8.4 and 6.7-11.2% for fortified milk- and soy-based formulas, respectively. HORRAT values ranged from 0.42 to 0.53, indicating that the precision of the method is acceptable. The mean RSD(r):RSD(R) values were 0.60 and 0.55 for milk- and soy-based formulas, respectively. As expected, RSDs for the unfortified samples were higher, but their HORRAT values (0.81 and 2.06) helped define a realistic limit of quantitation as 0.05 microg/g. Recovery data were quantitative and varied between 81.4 and 98.0% (mean = 89.8%) for each of 6 spiked materials.     

A new spectrum technique based on direct detection of light intensity absorbed

ＢｏｔｈＵＶＶｉｓｓｐｅｃｔｒｏｐｈｏｔｏｍｅｔｒｙａｎｄｆｌｕｏｒｏｍｅｔｒｙａｒｅｉｍｐｏｒｔａｎｔａｎｄｅｆｆｅｃｔｉｖｅｍｅｔｈｏｄｓｏｆｓｐｅｃｔｒｏｍｅｔｒｙ[1,2].Ｔｈｅｙｈａｖｅｂｅｅｎｐｌａｙｉｎｇａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｔｈｅｓｔｕｄｙｏｎｔｈｅｓｅｑｕｅｎｃｅｏｆｂｉｏｌｏｇｉｃａｌｍｏｌｅｃｕｌｅｓ,ａｎａｌｙｓｉｓｏｆｂｉｏｌｏｇｉｃａｌｍｏｌｅｃｕｌｅｓ,ａｎｄｂｉｏｌｏｇｉｃａｌｍｅｄｉｃｉｎｅａｎａｌｙｓｉｓ.Ｉｎｇｅｎｅｒａｌ,ｔｈｅｓｅｎｓｉｔｉｖｉｔｙｏ…     

Modeling the dynamic equilibrium between oligomers of (AlOCH3)n in methylaluminoxane (MAO). A theoretical study based on a combined quantum mechanical and statistical mechanical approach

Density functional theory (DFT) has been used to calculate the energies of 36 different methylaluminoxane (MAO) cage structures with the general formula (MeAlO)n, where n ranges from 4 to 16. A least-squares fit has been used to devise a formula which predicts the total energies of the MAO with different n's giving an rms deviation of 4.70 kcal/mol. These energies in conjunction with frequency calculations based on molecular mechanics have been used to estimate the finite temperature enthalpies, entropies, and free energies for these MAO structures. Furthermore, formulas have been devised which predict finite temperature enthalpies and entropies for MAO structures of any n for a temperature range of 198.15-598.15 K. Using these formulas, the free energies at different temperatures have been predicted for MAO structures where n ranges from 17 to 30. The free energy values were then used to predict the percentage of each n found at a given temperature. Our calculations give an average n value of 18.41, 17.23, 16.89, and 15.72 at 198.15, 298.15, 398.15, and 598.15 K, respectively. Topological arguments have also been used to show that the MAO cage structure contains a limited amount of square faces as compared to octagonal and hexagonal ones. It is also suggested that the limited number of square faces with their strained Al-O bonds explain the high molar Al:catalyst ratio required for activation. Moreover, in this study we outline a general methodology which may be used to calculate the percent abundance of an equilibrium mixture of oligomers with the general formula (X)n.     

Naphtho[2,3-d]-2-selena-l,3-diazole as a reagent for the determination of macro to submicro quantities of palladium

Five analytical procedures, gravimetric, spectrophotometric, radiometric, fluorometric and atomic-absorption, have been developed for the determination of macro to submicro amounts of palladium. The methods are based on the reaction of PdCl(2), with naphtho[2,3-d]-2-selena-l,3-diazole. Analytical conditions such as the reaction time, concentration ranges, effect of pH and of 68 foreign ions, and solvent extraction were studied. Information relating to the structure and formula of palladium-piazselenol reaction products is included.     

Is there any convergence between the differential and integral procedures used in chemical kinetics,particularly in nonisothermal kinetics?

Some contradictions concerning the classification of the methods to evaluate nonisothermal kinetic parameters into differential and integral ones are analyzed. Using the theorem of media for integrals, the equivalence between the methods that use the integration on low ranges of variables and the differential methods is shown. Concerning the magnitude of the range of change of variables on which the integration of the rate equation is performed, the applicability of the isoconversional methods that use approximate expressions of the temperature integral (Simpson's formula, formula based on the theorem of media for integrals) was analyzed. Our results were verified for simulated data (which are not affected by the experimental errors) as well as for the nonisothermal data for the thermal decomposition of ammonium perchlorate. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 339–344, 2006