Computer-aided method for simultaneous determination of substances in solution by spectrophotometry

A computer program, LESSDAD (East-Squares Spectrophotometric Determination by Absorbance Data), is described for computation of the best set of analytical concentrations of two ligands and/or metal ions from absorbance measurements. A least-squares method is used to calculate the concentrations from the pH of the solution, spectrophotometric data (experimental absorbances and known molar absorptivities) and the relevant equilibrium constants. The Newton-Raphson iteration is used to solve the mass-balance equations. The program is rapid and convenient to use and gives satisfactory results on a number of systems.     

Microprocessor-controlled system for automatic acquisition of potentiometric data and their non-linear least-squares fit in equilibrium studies

A microprocessor-controlled potentiometric titration apparatus for equilibrium studies is described. The microprocessor controls the stepwise addition of reagent, monitors the pH until it becomes constant and stores the constant value. The data are recorded on magnetic tape by a cassette recorder with an RS232 input-output interface. A non-linear least-squares program based on Marquardt's modification of the Newton-Gauss method is discussed and its performance in the calculation of equilibrium constants is exemplified. An HP 9821 desk-top computer accepts the data from the magnetic tape recorder. In addition to a fully automatic fitting procedure, the program allows manual adjustment of the parameters. Three examples are discussed with regard to performance and reproducibility.     

High-speed computers as a supplement to graphical methods--V. HALTAFALL, a general program for calculating the composition of equilibrium mixtures

A computer program, HALTAFALL, is described which calculates the equilibrium concentrations of the species in mixtures of any number of components, which can form any number of complexes and solid phases, provided concentrations (or partial pressures) can be used in the equilibrium calculations. Of course, the equilibrium constants must be known and enough data be given about the gross composition. Some applications are indicated. The flexible input rules make it applicable to a variety of problems. From the input information, the program itself devises an efficient plan for solving the simultaneous equations. The program also provides an efficient means of finding out which of many possible solid phases can actually appear in a certain equilibrium mixture.     

Automatic extraction of relevant peaks and reconstruction of mass spectra for low signal-to-noise GC-MS data

A method for the automatic extraction of spectra from GC-MS data is described. The program localizes chromatographic peaks and provides a reconstructed spectrum of each compound. It is particularly designed for low-sampling conditions frequently encountered with efficient GC columns, requiring threshold methods rather than methods based on peak shape; automatic threshold adjustments on the mass chromatograms are thus performed at different stages of the process. A test of the program on two sets of experimental data revealed better performances than manual data treatment, particularly in the case of low signal-to-noise ratios.     

Investigation of equilibria in solution. Determination of equilibrium constants with the HYPERQUAD suite of programs

A new suite of 10 programs concerned with equilibrium constants and solution equilibria is described. The suite includes data preparation programs, pretreatment programs, equilibrium constant refinement and post-run analysis. Data preparation is facilitated by a customized data editor. The pretreatment programs include manual trial and error data fitting, speciation diagrams, end-point determination, absorbance error determination, spectral baseline corrections, factor analysis and determination of molar absorbance spectra. Equilibrium constants can be determined from potentiometric data and/or spectrophotometric data. A new data structure is also described in which information on the model and on experimental measurements are kept in separate files.     

Computer calculation of equilibrium constants of species present in mixtures of metal ions and complexing agents

A general computer program is described for the interpretation of pH titration data for mixtures containing the ions of up to two metals and up to two ligands. The program, which employs the non-linear least-squares method, may be used to calculate equilibrium constants for hydrolysed metal ions, protonated ligands, and simple, protonated, hydrolysed, polynuclear, and mixed complexes.     

On some relations between advancing, receding and Young's contact angles

Problems of experimental determination and theoretical verification of equilibrium contact angles are discussed basing on the literature data. A relationship between the advancing and receding contact angles versus the equilibrium contact angle is described and then verified using the literature contact angles determined on paraffin wax and polypropylene. Using the proposed relationship and experimentally determined equilibrium contact angles, obtained by plotting the advancing and receding contact angles versus the contact angle hysteresis or by applying vibration of the system liquid drop/solid surface, it is found that the same value of the surface free energy for paraffin wax is calculated from the contact angles of water and ethylene glycol. However, in the case of polypropylene some inconsistency appears between the equilibrium contact angles of the probe liquid used and the calculated surface free energy. More experimental data of the equilibrium contact angle are needed to verify further the relationship.     

Reaction and phase equilibria of esterification of isoamyl alcohol and acetic acid at 760 mm Hg

The thermodynamic behavior of esterification reaction equilibrium and vapor–liquid equilibrium (VLE) of acetic acid and isoamyl alcohol mixture and its products, isoamyl acetate and water were investigated in this study. The experiments of chemical and phase equilibria were conducted in an Othmer type equilibrium cell. Since this esterification reaction proceeds very slowly, thus, a commercial Y type zeolite, NaY catalyst, was added to accelerate reaction rate such that the reaction equilibrium will be reached sooner and before phase equilibrium is considered. Using experimental data and phase and reaction equilibrium equations, the reaction equilibrium constants were calculated at different temperatures. The experimental results showed that the reaction equilibrium constant was very slightly dependent on temperature. The experimental data were then correlated by the Wilson, NRTL, and UNIQUAC models with the consideration of association effect of acetic acid in vapor phase. The concept of transformation composition by Barbosa and Doherty [D. Barbosa, M.F. Doherty, 1987, Proc. R. Soc. London Ser. A 413, 443–459.] was applied to construct three-dimensional figures showing experimental data and the calculated composition surfaces. It is observed from figures that the reactive azeotropy described by Barbosa and Doherty does not exist for this quaternary mixture. This study provides the required thermodynamic information for the development and design of this esterification process.     

Structural Relaxation in Amorphous Solids Studied by Thermal Analysis Methods

Structural relaxation for simple and more complex thermal histories is described by a phenomenological model based on a non-exponential relaxation function, the reduced-time concept and the nonlinear structural contribution to the relaxation time. The history, development of experimental techniques and data analysis is described. It is shown that the volume and enthalpy relaxation response can conveniently be compared on the basis of a fictive relaxation rate, R _f. A simple equation relating R _f and the parameters of the phenomenological model is given. The calculated data for moderate departures from equilibrium are in good agreement with our experiments and data previously reported in the literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

A computational approach to the spectrophotometric determination of stability constants-II Application to metalloporphyrin-axial ligand interactions in non-aqueous solvents

The ability of the computer program SQUAD to deduce a plausible equilibrium model, associated stability constants and spectra of individual species is described. The original version of SQUAD has been extensively modified and these changes are detailed. In particular a "user-friendly" method of data input has been implemented that simplifies familiarization with the program. Brevity of program code has been sacrificed in favour of the new data input and error-checking features of SQUAD, with beneficial results. The application of SQUAD to five non-aqueous metalloporphyrin-axial ligand interactions exemplifies the program's ability to handle widely different types of equilibrium systems.     

A PC compatible computer program for the calculation of equilibrium constants by the simultaneous processing of different sets of experimental results

A new PC compatible computer program SIRKO for the calculation of the equilibrium constants by means of the simultaneous processing of different experimental data from various techniques is given. This program is characterized by the application of a universal response function, which allows many different physicochemical methods to be used to study equilibria without any modification of the program. It is also possible to refine additional parameters (electrode parameters, initial analytic concentration, etc). We have used the least-squares method with the weightings calculated according to the error propagation rule taking into account all independent variables. To minimize the function, singular Jacobian decomposition is applied. This allows control of its range and forms a set of parameters, determined from the experimental data.     

水化介孔氧化硅表面酸碱平衡常数的测定

采用自动电位酸碱滴定技术研究了水化介孔氧化硅的表面脱质子反应.基于悬浮液的酸碱滴定数据,用Gran图法计算得到了介孔氧化硅表面氢离子键位点浓度.利用FITEQL4.0软件,采用双电层恒电容模型计算得到了相应的表面酸碱平衡常数.结果表明,与无定形氧化硅不同,介孔氧化硅表面存在对应于双齿表面硅羟基≡Si2OH和单齿表面硅羟基≡SiOH的两个脱质子常数,分别为pKa1=6.78±0.15,pKa2=10.25±0.22.根据测定得出的介孔氧化硅表面脱质子常数,构建了不同pH条件下,介孔氧化硅表面优势组分分布图,并讨论了表面电容预赋值对氧化硅表面组分分布的影响.     

冠醚取代酞菁超分子体系的光谱性能研究

本文合成了苯并[15-冠-5]取代的酞菁化合物,研究了铷离子诱导的冠醚酞菁二聚行为的光谱特性,观察到冠醚酞菁形成二聚体的光谱变化分三阶段进行,与铷离子的浓度密切相关,这是由于二聚体中酞菁环从非共平面构象最终转变为面对面的超分子结构的结果;详细介绍了对紫外可见吸收光谱中重叠光谱的数据处理方法,从而计算了二聚体形成的平衡常数K值。     

In Process Citation

The basic computer program MICMAC has been developed to fit equilibrium constants to various types of experimental data with a microcomputer. The program uses the very efficient Gauss-Newton-Marquardt algorithm for non-linear least-squares multiparametric refinement. Highly interactive, convenient to use and of modular design, it allows for a rigorous weighting scheme, and it takes account of possible systematic errors. This program is useful for solving problems with several sets of experimental data. Some examples dealing with polarography, pH-metric titration and (13)C-NMR are given, illustrating the versatility of MICMAC. Comparison is made with some recently published programs.     

乙烯在四氯化亚铜铝甲苯溶液中溶解度测定及其热力学模型

实测了乙烯在四氯化亚铜铝甲苯溶液中的溶解度。提出了一个处理伴有化学反应的气液平衡的热力学模型, 同时考虑了体系的相平衡和络合平衡, 将Scatchard-Hildebrand模型适当简化后, 计算其液相活度系数, 编制了计算程序, 模型应用方便。用该模型关联计算了溶解度实验数据, 结果令人满意。     

POLAG-a general computer program to calculate stability constants from polarographic data

A general computer program, POLAG, that will calculate stability constants from polarographic data, has been written. The program requires no pretreatment of the experimental data. Any equilibrium model, consisting of species having the general formula M(m)H(j)(OH)(k)L(n)L'(p) may be fitted to the data. The performance and versatility of POLAG has been demonstrated by reprocessing polarographic data previously published by four different research groups.     

Modeling of the kinetics of nickel reduction from a multicomponent oxide melt with a gaseous reducing agent

A model was suggested that allows the kinetics of bubbling of various reducing gases through an oxide melt to be described by thermodynamic equilibrium calculations without the use of experimental data. An algorithm for calculations was developed. The model is tested for the NiO-FeO-Al₂O₃-SiO₂-CaO-Mg-CO-CO₂ system. A comparative analysis of the calculation results and experimental data showed that the suggested technique could be used in a qualitative analysis of interactions between multicomponent oxide melts and gaseous reducing agents of various compositions. Calculations describing the kinetics of reduction of nickel oxide with hydrogen in the NiO-CaO-B₂O₃ system over the temperature range 1473–1973 K were performed.     

Computer evaluation of water sorption on ion exchangers

Water sorption on an ion exchanger can be described by formation of several hydrates. The general least squares program WSLET based on the "pit-mapping" approach has been written for evaluating such equilibria. It is written in FORTRAN 77 for use on personal computers. Besides finding the best values for the equilibrium constants of the various hydrates the program also searches for best values of the stoichiometric indices by using the so-called ESI-method. The program is provided with least-squares procedures and blocks for statistical analysis of the residuals as well as for data simulation. It has been tested with data on the strong base resin Dowex 1 as well as on simulated data. In the present paper an illustrative example is given together with data simulation. It is found that in most cases WSLET helps to find a better fit than earlier models quite efficiently, showing the advantage of the ESI method in combination with least-squares methods.     

Computer analysis of amino acid chromatograms.

A procedure is described for the automatic off-line analysis of amino acid chromatograms of protein hydrolysates, using a small computer. The data requirements are basic, and, unlike previous programs, the present system allows the separation and identification of bands, as well as the quantitative determination of composition. With minor modification, the program could be extended for use with most types of chromatographic data. The validity of the application of the program to experimental data is discussed.     

An algorithm and a fortran program (chemequil-2) for calculation of complex equilibria

A computer program, CHEMEQUIL-2 (CHEMical EQUILibrium), based on interfacing an iterative algorithm with the Newton-Raphson method, for calculating equilibrium compositions in aqueous mixtures of metals and ligands, is described. The program is also capable of simulating acid-base titrations. It has been compared with MINIQUAD, COMPLEX and MINEQL with respect to execution time and memory requirements. As a result of algorithm development and program design, CHEMEQUIL-2 offers considerable savings in both execution time (by 1–2 orders of magnitude) and memory requirements, especially for large problems, compared to these programs. The computational efficiency of CHEMEQUIL-2 makes it well suited for use in hydrogeochemieal transport models.