Contributions to the theory of catalytic titrations--I: Complexometric catalytic titrations

Complexometric catalytic titrations with both volumetric and coulometric addition of the titrant have been simulated. By taking into consideration the equilibrium concentration of the catalyst during the titration, general mathematical equations have been set up. The influence of several factors on the shape of the simulated catalytic titration curve has been investigated and is discussed. The work also deals with the conditions under which the approximate mathematical expressions (equilibrium concentration of the catalyst being neglected) can be applied to simulate the catalytic titration curves with a satisfactory accuracy.     

Contributions to the theory of catalytic titrations-II Precipitation and redox catalytic titrations

Precipitation and redox catalytic titration curves, obtained by both volumetric and coulometric addition of the titrant, have been simulated, taking into account the equilibrium concentration of the catalyst during the titration. The influence of several factors on the shape of the simulated catalytic titration curves has been investigated and is discussed in detail. Simulations of the blank titrations have also been made.     

Complexometric catalytic titrations using the indicator reaction periodate-triethanolamine

The possibility of applying a new indicator reaction, i.e., periodate-triethanolamine, as the indicator in titrations of ethylenediamine-N,N,N′,N′-tetracetic acid (EDTA), 1,2-diaminocyclohexanetetraacetic acid (DCTA), and diethylenetriaminepentaacetic acid (DTPA) with standard manganese(II) sulfate solution (phosphate buffer pH 6.84) has been investigated. The titration course was followed potentiometrically using a perchlorate ion-selective electrode. The optimum conditions for determinations in relation to concentration of the indicator reaction components have been established. Furthermore, the influence of some ions on the possibility of EDTA determination was considered and maximally tolerable concentrations under these conditions were established. The amounts of 0.170–18.00 mg of EDTA, 0.150–16.00 mg of DCTA, and 0.180–19.00 mg of DTPA were determined with a maximal relative standard deviation less than 1.0%. Results are in good agreement with those of comparable methods. Finally, the experimental catalytic titration curves obtained in this way are compared to the simulated ones.     

Semiautomatic and automatic catalytic amperometric and catalytic constant-current potentiometric titrations of gold(III)

Semiautomatic and automatic amperometry and constant-current potentiometry were used to follow the course of catalytic titration of gold(III) with potassium iodide. The Ce(IV)-As(III) system in the presence of sulfuric acid was used as the indicator reaction. The possibilities of the application of two types of graphite electrodes were investigated. The effect of concentration of the indicator reaction components, and the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 80–900 μg of gold(III) were determined with a relative standard deviation less than 1.1%. The results obtained are in good agreement with those of comparable methods.     

Acid-base, electron donating and catalytic properties of sulfated zirconia

The electron donating properties of sulfated zirconia were studied from the adsorption of electron acceptors of various electron affinity. The surface acidity and basicity of the oxides have also been determined by titration method using a set of Hammett indicators. The data have been correlated with the catalytic activity of the oxide towards esterification of acetic acid usingn-butanol, reduction of cyclohexanol in 2-propanol and oxidation of cyclohexanol with benzophenone.     

Determination of some dithiocarbamates by catalytic thermometric titration

The determination of dithiocarbamates by catalytic thermometric titration is described. The dithiocarbamates can be determined in the range 0.5-20 mumole with relative errors of about 5%.     

Determination of organic bases in non-aqueous solvents by catalytic thermometric titration

Catalytic thermometric titrations have been developed for bases (brucine, diethylaniline, potassium acetate and triethylamine) in acetic acid by continuous and discontinuous addition of the standard solution and automatic temperature recording. The determination of weak bases, e.g., antipyrine, unsuccessful in acetic acid by catalytic thermometric titration, has been achieved by using nitromethane or acetic anhydride as solvent. Catalytic thermometric titrations were also performed by coulometric generation of hydrogen ions for the determination of micro amounts of weak bases in a mixture of acetic anhyride and acetic acid.     

Indirect determination of some aliphatic secondary amines by catalytic thermometric titration

The determination of some secondary aliphatic amines by catalytic titration is described. The amines can be determined in the range 0.1-5 mumole with relative errors of about 3%.     

Automatic catalytic titration of silver

An automatic method is described for the catalytic titrimetric determination of microgram amounts of silver. The method is simple and accurate, and is based on the inhibitory effect of silver ions on the iodide-catalysed Ce(IV)-As(III) reaction. The end-point of titration with iodide is determined either automatically by the second- derivative technique or from the recorded potentiometric or spectrophotometric curves. Microamounts of silver in the range 1–2000 μg were determined with relative errors of about 0.7%.     

Determination of manganese in grain by potential titration with catalytic end-point indication

A method of catalytic potential titration for the determination of trace manganese by using crystal violet ion selective electrode is reported in this paper. It is based on the catalytic effect of manganese (II) on the oxidation of crystal violet by potassium periodate in the presence of nitrilotriacetic acid (NTA). The experiments indicated that this technique showed high sensitivity and high accuracy. The results of determination of trace manganese in grain could be compared with the results obtained by means of atomic absorption spectrometry.     

A comparison of cationic polymerization and esterification for end-point detection in the catalytic thermometric titration of organic bases

A systematic comparison has been made of two indicator systems for the non-aqueous catalytic thermometric titration of strong and weak organic bases. The indicator reagents, alpha-methylstyrene and mixtures of acetic anhydride and hydroxy compounds, are shown to give results (for 14 representative bases) which do not diner significantly in coefficient of variation or titration error. Calibration graphs for all the samples, in the range 0.01-0.1 meq, are linear, with correlation coefficients of 0.995 or better. Aniline, benzylamine, n-butylamine, morpholine, pyrrole, l-dopa, alpha-methyl-l-dopa, dl-alpha-alanine, dl-leucine and l-cysteine cannot be determined when acetic anhydride is present in the sample solution, but some primary and second amines can. This is explained in terms of rates of acetylation of the amino groups.     

Some observations on catalytic conductometric titrations

Conductometric and high-frequency conductometric methods for the determination of the endpoint of catalytic titrations were developed. Titrations of sodium acetate were made in a mixture of acetic anhydride and acetic acid (7:3–11:3) which was 0.05–0.1 mol dm⁻³ in sodium perchlorate. Integral and derivative titration curves were recorded in both coulometric and volumetric titrations. Different acylation reactions, as well as dehydration of formic acid, were used as the indicator reactions. The optimal conditions of determination—choice of volume ratio of acetic anhydride to acetic acid, rate of the titrating reagent addition, concentration of sodium perchlorate, and concentration of several alcohols, water, and formic acid as components of the indicator reactions—were determined. Using the catalytic conductometric method, amounts of 0.04–11 mg of sodium acetate were determined with a relative standard deviation of less than 0.8 and 1.6% in volumetric and coulometric addition, respectively. Using the catalytic high-frequency conductometric method, amounts of 1–11 mg of sodium acetate were determined with relative standard deviation less than 0.5% (volumetrically) or less than 1.4% (coulometrically). The obtained results were compared with those of potentiometric and catalytic thermometric titrations.     

催化滴定 III: 影响EDTA滴定金属离子时突跃的因素

本文探讨以催化反应指示终点直接用EDTA滴定金属离子时影响突跃的因素. 采用滴定曲线突跃部分的斜率, tanθ, 作为指示反应速率的表征. 通过实验探讨了PH、CuEDTA和NiTrien用量以及滴定速率对tanθ的影响, 并从理论上导出tanθ的近似表达式, 它是NiTrien的起始浓度、加入EDTA的速率以及EDTA与NiTrien的反应速率常数三个变量的线性函数, 利用这一表达式可对实验结果作出较为满意的解释.     

Chemical properties of the surface of nanofibrous carbonaceous materials produced by catalytic methane decomposition

The chemical behavior of nanofibrous carbonaceous materials prepared by the catalytic decomposition of methane was studied by IR spectroscopy, X-ray photoelectron spectroscopy, and titration. Initial carbon was shown to be virtually devoid of functional groups on its surface. Treatment of carbonaceous samples with alkali, ammonia, or nitric acid modified the surface of carbon and increased the number of functional groups.     

Simulation of butadiene rubber synthesis on cobalt- and neodymium-containing catalytic systems in reactor cascades with heat removal

The synthesis of butadiene rubber on cobalt- and neodymium-containing catalytic systems in a reactor cascade has been simulated taking into account heat removal through the reactor jackets. The problem of optimization of the operating regime has been solved for butadiene polymerization in a cascade of continuous reactors. The regions of initial process parameters admissible for obtaining a high-quality rubber have been determined.     

Catalytic amperometric and catalytic constant-current potentiometric titrations of silver(I), palladium(II) and mercury(II)

Amperometry and constant-current potentiometry were used to follow the course of catalytic titrations of silver(I), palladium(II), and mercury(II) with potassium iodide. The Ce(IV)As(III) and Ce(IV)Sb(III) systems in the presence of sulphuric acid were used as indicator reactions. The possibilities of application of platinum, palladium, gold, graphite, and glassy-carbon indicator electrodes were investigated. Graphite appeared to be somewhat more advantageous than the other electrode materials. The effect of concentration of the components of the indicator reactions, the presence of organic solvents and acids on the shape of the catalytic titration curves was studied. Amounts of 30-3000 mug of silver(I) nitrate, 90-900 mug of palladium(II) chloride, 130-1300 mug of mercury(II) chloride, and 150-1500 mug of mercury(II) nitrate were determined with a relative standard deviation less than 1.0%. The results obtained were in good agreement with those of comparable methods. The catalytic titration method developed was applied to determination of mercury in Unguentum Hydrargyri.     

煤焦催化气化活性位扩展模型的研究

针对煤催化气化反应中传统的煤气化动力学模型不再适用或应用范围受到限制的现实，从催化作用机理分析入手，以煤焦CO2催化气化为研究对象，建立了描述气化反应速率与转化率关系的动力学模型——活性位扩展模型。并以KCl催化剂及K-Ni(10%Ni)复合催化剂作用下神府煤焦CO2气化的实验结果对模型进行验证。结果表明，活性位扩展模型很好地体现了煤焦催化气化的动力学规律，即催化剂的添加，有效地增大了反应界面处的活性部位和活性表面积，使气化反应在更温和的条件下快速进行；模拟值与实验值吻合较好，最大偏差10%。由于反应初期的传质阻力不可忽略，实验值与模拟值存在一定误差。     

Determination of total free acid in formaldehyde by coulometric catalytic thermometric titration

Coulometric catalytic thermometric titration of the total free acid (HCOOH) in formaldehyde of various manufacturers was successfully performed. The indicator reaction was the exothermic polymerization of formaldehyde in the presence of ethanol, catalyzed by strong base. In the titrations, a cathodically polarized platinum generator electrode was employed. The content of free acid in various formaldehyde samples ranged between 0.018 and 0.044 %, and was determined with a standard deviation less than 1.5%. Good agreement was obtained with the results of coulometric photometric and volumetric titrations.     

Importance of the definition of catalytic properties for the commutability of an enzyme reference material: example of lipase

Assays for pancreatic lipase activity in serum need the use of calibrators, but there is a lack of a reference method and of a reference material. Under routine conditions, comparability of lipase catalytic activities was found to be poor when lipase was determined in 50 patients’ specimens by a turbidimetric (Boehringer) and a colorimetric (Sigma) assay. Mean values of the results differed by a ratio of 2.39. Catalytic properties of three materials, two commercial calibrators and a home-purified preparation of human pancreatic lipase (HPL), have been compared in titrimetry at constant pH. Optimal common conditions were defined for the titration of lipase activity in the three materials. When using these titres for each calibrator, comparability was greatly improved (ratio = 1.25). This result indicates that a significant part of between-method discrepancy was due to the lack of a reference method for the titration of lipase calibrators. The inter-method behavior of each material was compared to that of patients’ specimens. Using HPL as calibrator, the comparability of patients’ results was still dramatically improved (ratio = 1.01). This study shows the importance of verifying the similarity of catalytic properties of an enzyme reference material to those of the corresponding enzyme in human specimens, in order to ensure its commutability. The use of validated commutable calibrators, traceable to certified reference materials, is an opportunity to improve the inter-method comparability of results in clinical enzymology.     

Modeling and simulation of stationary catalytic processes

Generalized models for steady state catalytic processes are presented in matrix form. Multistep reaction rate control is assumed. Numerical algorithms for solving of the created linear and nonlinear equation systems are developed and tested. Four examples are considered: an Eley–Rideal-mechanism, a Langmuir–Hinshelwood mechanism, a dual route, dual site mechanism, and a monomolecular decomposition with steady state multiplicity. The overall reaction rates are simulated as a function of the reactant concentrations. A maximum reaction rate is obtained in the case of a Langmuir–Hinshelwood mechanism (example 2), the location of the rate maximum in the concentration domain is shifted towards the concentration of the reactant with the lowest adsorption constants. An Eley–Rideal mechanism (example 1) has always monotonously increasing rate curves. In the case of steady state multiplicity (example 4) all steady states could be simulated with the proposed algorithm. The computation of reaction rate surfaces is important in investigating the behavior of complicated catalytic systems (e.g., systems with multistep rate control and/or steady state multiplicity), in planning of experiments and in chemical reactor simulation.