Spectrophotometric kinetic methods

F Spectrophotometric Kinetic Methods 381 14G Spectrophotometric Studies of Complex Ions 384 Questions and Problems 390... 

A kinetic method for the determination of 2,4-dinitrophenol is proposed. The method is based on the inhibiting effect of 2,4-dinib ophenol on the Mn(II) catalysis of the oxidation of malachite green with potassium periodate. The reaction was followed spectrophotometrically at 615 nm. The optimal experimental conditions for the determination of 2,4-dinitrophenol were established under the optimal reaction conditions ... 

The kinetics of this reaction can be very conveniently followed by measuring the volume of carbon dioxide liberated in a given time, and the earlier studies employed this technique, though more recently spectrophotometric (uv) methods have been favoured. Most of the kinetic studies have been directed towards determining whether the SE1 or A-SE2 mechanisms, equilibria (257) and (258) or (259) and (260), respectively,... 

Determined by spectrophotometric methods (Cramer et al., 1967). Determined by kinetic methods (VanEtten et al., 1967a). 

Glew, D.N., Roberson, R.E. (1956) The spectrophotometric determination of the solubility of cumene in water by a kinetic method. J. Phys. Chem. 60, 332-337. 

Kinetic spectrophotometric determination methods for Ag(I) were proposed, based on the strong catalytic effect of this ion on the controlled oxidation of various dyes, by measuring the rate of change of absorbance. Some recently published examples are Ag(I)-catalyzed peroxodisulfate oxidation of brilliant cresyl blue (33)104 or gallocyanine (34)105, both in the presence of 1,10-phenanthroline (35) and hexacyanoferrate (36) oxidation of indigo carmine (37)106. 

Detector Noise and Drift. Transducers for modem spectrophotometric systems are usually vacuum phototubes or photomultiplier tubes. Noise and drift from the transducer can be quite troublesome in kinetic methods, and special care is normally taken to ensure low-noise operation. 

Spectrophotometric methods Kinetic methods, in parenthesis, extrapolated values. 

A more detailed description of the electron transport chain was obtained by using three other methods selective inhibition, spectrophotometric kinetics, and determination of the respective oxidation-reduction potentials. The first two methods are based on the spectral properties of the various components of the electron transport chain. It is indeed fortunate that the pyridine nucleotides, the cytochromes, and the flavoproteins have specific absorption spectra, and that the spectra undergo considerable changes when they pass from the reduced to the oxidized form. 

A number of applications of the kinetic methods are presented in Sections 2—5 which we hope will clearly show the power of the methods to distinguish between simple and complex kinetic systems using conventional spectrophotometric and digital recording equipment. 

Qg Exchangeable organic iodine determined by kinetic methods. + Estimation by spectrophotometric of Heedman et al. (4) tr Iodine prophylaxis or pretreatment with iodine. 

Pandey, S. McHale, M. E. R. Horton, A. M. et al. Kinetics-Based Indirect Spectrophotometric Method for the Simultaneous Determination of Mn04 and Gt207 ,... 

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Exploitation of analytical selectivity. We have seen, in our discussion of the A —> B C series reaction (Scheme IX), that access to the concentration of A as a function of time is valuable because it permits to be easily evaluated. Modern analytical methods, particularly chromatography, constitute a powerful adjunct to kinetic investigations, and they render nearly obsolete some very difficult kinetic problems. For example, the freedom to make use of the pseudoorder technique is largely dependent upon the high sensitivity of analytical methods, which allows us to set one reactant concentration much lower than another. An interesting example of analytical control in the study of the Scheme IX system is the spectrophotometric observation of the reaction solution at an isosbestic point of species B and C, thus permitting the A to B step to be observed. 

Almost all kinetic investigations on azo coupling reactions have been made using spectrophotometric methods in very dilute solutions. Uelich et al. (1990) introduced the method of direct injective enthalpimetry for such kinetic measurements. This method is based on the analysis of the zero-current potential-time curves obtained by the use of a gold indicator electrode with a surface which is periodically restored (Dlask, 1984). The method can be used for reactions in high (industrial) concentrations. 

The kinetics of deacylation of 2,4-6-trimethyl, 2,4,6-triethyl and 2,4,6-tri-wo-propylbenzaldehyde have been determined over a wider acid range (50-100 wt. % sulphuric) than used in the above study, the reaction rates being determined either by a spectrophotometric or gasometric method, the latter being suitable here... 

Iododestannylation has been the subject of two kinetic investigations using the spectrophotometric method, the results of which differ according to the solvent... 

Maeder, M., Gampp, H. Spectrophotometric data redudion by eigenvedor analysis for equilibrium and kinetic smdies and a new method of fitting exponentials. Anal. Chim. Acta 1980, 122, 303-313. 

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