Titrimetric Investigations

Wyman and collaborators presented conclusive experimental evidence that Conant s assumption was justified—that imidazole residues of histidine must be linked to the iron in hemoglobin. The differential acid-base titration data of German and Wyman (30) between hemoglobin and oxyhemoglobin were taken as the base for calculations by Wyman (92), and these established the existence in hemoglobin of two acid groups (pK 5.25 and 7.81). On oxygenation, these values shifted to 5.75 and 6.80. 

Since the apparent heat of dissociation of the groups titrated between pH 5.5 and 8.5 fitted the values (Q = 6500 cal. per mole) for the imidazole nucleus, Wyman drew the conclusion that in hemoglobin, histidine residues are linked to the iron. Wyman and Ingalls (93) extended the differential titrations to hemi- and hemoglobin, and found the following pK values at 25°C. and at ionic strength m = 0.16  

Theorell s (79) differential titration of horse hemi- and hemoglobin at 20° and low ionic strength yielded the values  

These values are in satisfactory, though not complete, agreement with the Wyman-Ingalls values, which, owing to war conditions, were unknown to the author. 

The titration difference between globin and hemiglobin was found to be one equivalent less than calculated. Different explanations are possible, but are still without experimental support. 

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In this experiment the effect of a mixed aqueous-organic solvent on the color transition range of common indicators is investigated. One goal of the experiment is to design an appropriate titrimetric method for analyzing sparingly soluble acids and bases. 

Experimentally, the measurement of reaction rates consists in investigating the rate at which starting materials disappear and/or products appear at a particular (constant) temperature, and seeking to relate this to the concentration of one, or all, of the reactants. The reaction may be monitored by a variety of methods, e.g. directly by the removal of aliquots followed by their titrimetric determination, or indirectly by observation of colorimetric, conductimetric, spectroscopic, etc., changes. Whatever method is used the crucial step normally involves matching the crude kinetic data against variable possible functions of concentration, either graphically or by calculation, until a reasonable fit is obtained. Thus for the reaction,... 

Singhal et al. [78, 79] have described a titrimetric method for the determination of low levels of Oxamyl residues in soils. Their investigations revealed that after hydrolysis Oxamyl gave a brown precipitate with carbon disulphide and an alkaline solution of copper(II) sulphate. This reaction suggested a procedure for the determination of Oxamyl by titration with ethylene diamine tetracetic acid of the copper remaining unreacted to the 1-(2 pyridylazo)-2-naphthol end-point indicator). The following stoichiometric reaction appeared to occur between Oxamyl and the reagents ... 

We return to spectrophotometric absorbance data and Beer s law Y=CA. The matrix C of concentration profiles, as computed by the relevant function, contains the profiles of all species that are part of the model. Remember, in kinetics this relevant function is an ODE solver, e.g. Runge-Kutta, while for equilibrium investigations, such as titrations, it is the Newton-Raphson routine that computes C. The following considerations hold for both kinetic and titrimetric absorbance data Y. 

The kinetics of hydrolysis of the sulfone of 3,7-dibenzothiophendi-sulfonyl chloride have been investigated in a 70% dioxane-water mixture. Hydrolysis rates were measured both conductometrically and titrimetrically. 

Three methods for determining mineral carbon dioxide in coal were investigated using bituminous coal. The titrimetric method is claimed to be superior to either of the then-used British standard gravimetric or manometric methods (BS 1016). The procedure involves the decomposition of carbonate minerals with hydrochloric acid and absorption of the evolved carbon dioxide in a mixture of benzylamine, ethanol, and dioxan. This mixture forms a stable salt of benzylcar-bamic acid, which is then titrated with sodium methoxide. The method was said to be suitable for all concentrations of carbon dioxide. It is especially accurate for low concentrations, and it is much more rapid than other methods tested. 

In the article of Kaarls and Quinn [34] primary methods are carefully defined as methods for the determination of the amount of substance in pure or simple compound systems, i.e. in samples which do not contain impurities acting as potential interferences. It is explicitly stated that it is a future task of the CCQM to investigate the applicability and robustness of these methods for complex mixtures encountered in practical analytical chemistry. Many other papers (e.g. [36]), however, tend to identify primary methods already as methods of analysis (to be used on complex samples of unknown overall composition). This over-optimistic (and unwarranted) enlargement of the definition implies that all titrimetric methods of analysis would be considered as primary methods putting aside any interference that occurs in complex samples. Considering all possible sources of error that may occur in both the stoichiometry of the reaction and with the determination of the equivalence point of a titration, this cannot be possible. Neither was this the intention of the CCQM. 

Even for reactions in which the Sij2 contribution to ionization is negligible, one does not have a means of estimating from solvolysis rates, the solvent activity coefficients for the transition state corresponding to ionization of RX. Although Vrx easily found from Henry s Law constants, and equation (16) does produce an activity coefficient for some transition state, this may not be a simple transition state corresponding to ionization of RX. Solvolysis rates may be smaller than ionization rates of many compounds, in certain solvents, because of ion-pair return, a phenomenon which has been firmly established by the investigations of Winstein et al. (1965). No matter whether Ag is a titrimetric rate constant 7... 

A pyrohydrolytic technique has been described for decomposing various inorganic fluorine-containing materials, including minerals.55 The temperature recommended is 1200 °C and the aqueous solution containing F is determined by a conventional titrimetric method. Fluorine on the surface of metallic samples can be determined rapidly and non-destructively by means of the prompt y-photons (837 keV resonance) of the 19F(p,ay)160 reaction 56 the experimental sensitivity of the method is approximately 5 x 10-4 (/xg F ) cm-2. The use of an electrode sensitive to F- to measure the adsorption of F by clay minerals and soils has been investigated.57... 

For an exact characterization of the investigated systems, besides the isotope ratio measurement, one has to carry out the quantitative analysis of polyethers, and of the corresponding metal complexes as well. The analysis method which is most commonly described in the literature for polyethers is NMR spectrometry However, this spectroscopic method is not very precise for a quantitative determination. Therefore, other types of analysis have been developed, e.g. a gravimetric procedure and a titrimetric method using the standard addition technique with a potentiometric indication... 

A systematic investigation of a titrimetric determination of reducing sugars with copper(ll) sulphate using the Lane and Eynon method has been reported. ... 

Grignard type compounds of some lanthanide metals in the oxidation state +2 have been investigated by D.F. Evans et al. (1970, 1971). Europium, samarium and ytterbium react in tetrahydrofuran with alkyl and aryl iodides between —20 and + 30°C forming colored solutions containing mixtures of compounds, which give some Grignard-type reactions. Characterization of the compounds was done only by magnetic susceptibility measurements and some titrimetric analyses. 

The investigations outlined above demonstrate the utility of electrochemical techniques in probing cluster reactions. The titrimetric bulk electrolysis procedure allows new cluster types to be prepared easily, with quantitative information on stoichiometry. The cyclic voltammetry approach permitted a systematic study of other ferredoxins to determine the factors that allow rapid reactions of this type to occur. It could be shown, for example, that the presence of Asp in place of Cys in the sequence was not sufficient to confer this striking ambivalence between cluster types. The 7Fe ferredoxin from Sulfolobus acidocaldarius, which also has the... 

The reduction of silver(i) by ascorbic acid, AHj, has been investigated using a titrimetric method. The rate is inversely dependent on hydrogen ion and the mechanism proposed,... 

The main components, namely the rare earth elements and also the Co or uon components can be analysed by standard gravimetric or titrimetric methods. Also the X-ray fluorescence is a very valuable tool in these investigations. A very important constituent, which is undesirable, is oxygen. The oxygen is usually determined by means of vacuum fusion. 

The surface characterization of a polymer particle involves investigating the adsorption of ions and amphiphilic molecules (emulsifiers, oligomers), determining the number of covalently bonded functional groups and acquiring information on the structure of the interfadal layer (swollen state or hairy layers ). Presently this task can not be solved satisfactorily. The main methods used are titrimetric analyses on purified dispersions, soap titration and electrokinetics. 

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