Titration Rate Research Articles

Computer‐ Controlled Automatic titration system and its application to the analysis of fats and oils

Abstract and SummaryAn automatic titration system (ATS) controlled by a microcomputer was developed for potentiometric or pH titrations. The titrator is equipped with a piston‐type glass buret which is operated by a stepping motor driven by computer‐generated pulse. The droplet volume of titrant is 0.00211 ml per pulse which enables very accurate titration. The titration rate is controlled by regulating the intervals of pulses according to the potential changes accompanying the progress of titration. The point giving the maximum pulse interval is detected automatically as the end point. Accordingly, it is not necessary to present the potential or pH value of the end point. Sample beakers are sent in turn with an endless mode. As examples of practical application of ATS, saponification value, amine value, acid value, total chlorine content, and chloride ion content were determined. The ATS makes it possible to contribute not only to the improvement of precision but to the simplification of analytical procedures in fats and oils chemistry.

Equivalence-point determinations for automated potentiometric titrations with ion-selective electrodes

An improved method is presented for determining the equivalence point in potentiometric titrations. Titration rate and data acquisition are under computer control, and ion-selective electrodes are used as indicators. As the titration proceeds, the potentiometric curve and Gran (antilog) plot are displayed on a CRT. Upon completion of the titration, the operator uses interactive graphic techniques to interrogate the Gran plot and develop an error function. This error function identifies the period during the potentiometric titration when the cell output is most nearly Nernstian. Data obtained during the identified period are used to estimate the equivalence point. Data are presented together with a discussion of the characteristic features of the error function.

Importance of SH groups in catalysis by bovine brain acid phosphatase

The rate of inactivation of acid phosphatase (EC 3.1.3.2) from bovine brain by dithiobis-(2-nitrobenzoic acid) (Nbs 2) is identical to the rate of titration of one of the two SH groups of this enzyme. The rate of inactivation of the enzyme by Nbs 2 is pH dependent and, at 300 mM NaCl, can be described by the reaction of a single SH group of pK 8.4. At low ionic strength the pK determined from the k inactivation VS. pH profile is 7.7 and the results deviate markedly from the predicted values at pH values ⩽6. The decrease of V upon addition of salts is paralled by the decrease of inactivation rate by Nbs 2. The relevance of SH groups in catalysis by bovine brain acid phosphatase is discussed in terms of these data.

The role of lysine and leucine binding on the catalytical and structural properties of aspartokinase III of Escherichia coli K 12.

The lysine‐sensitive aspartokinase of Escherichia coli K12, a 100000‐molecular weight dimer, possesses four binding sites for L‐lysine, its allosteric inhibitor. The lysine binding is cooperative. In the presence of leucine this cooperative effect disappears, that may explain the synergistic inhibition phenomenon observed between these two amino acids. The four sites are non‐equivalent two by two, with a K of, respectively, 8 μM and 100 μM. The tetramerization of the protein observed in the presence of lysine appears not to be related to the inhibition of enzyme activity. Lysine or leucine binding leads to transconformational changes evidenced by difference spectra and modification in – SH titration rates. All the results are consistent with the hypothesis that the lysine‐sensitive aspartokinase belongs to the class V of allosteric enzymes.

Automatic titrator for amperometric analysis

A digital controlled apparatus for the simultaneous automatic amperometric titration of up to four samples is described. In the vicinity of the endpoint the titration rate is automatically reduced to a preselected level. The current values are punched on paper tape for computer evaluation.

Structure-activity relationship in tryptophanyl-transfer ribonucleic acid synthetase from beef pancreas. Role of -SH groups in the activity of the enzyme.

The titration of the – SH groups of beef pancreas tryptophanyl‐tRNA synthetase by N‐ethylmaleimide and the consequent effect on the exchange and transfer reactions of the enzyme were examined.The 16 sulfhydryl groups of the native dimeric enzyme do not react homogeneously at pH 7, with 1 mM reagent. They can be divided into three classes with decreasing reactivities. The reaction of the first class (6 – SH groups) has no effect on activity. The reaction of the second class (4 – SH groups) brings about an increase of Km(app) for tryptophan both in the exchange and in the transfer reactions of the enzyme. The activity of the enzyme is lost during reaction of the third class (6 ‐ SH groups). This is evidenced by the decrease of the V of the [32P]PPi‐ATP isotope exchange and tRNA aminoacylation reactions and by the decrease in the amount of the tryptophanyladenylate · enzyme complex isolatable on Biogel P30. The destruction of the active site by alkylation of the sulfhydryl groups of class III can be the consequence of a structural change of the enzyme induced by the chemical modification. During the alkylation of the first two classes of ‐ SH groups the Km(app) for ATP, PPi and tRNA are not altered significantly.The presence of tryptophan or tryptophanyladenylate reduces the rate of titration of the ‐SH groups of class II and class III and in a parallel fashion the rates of increase of Km(app) for tryptophan and of decrease of V. The titration of the –SH groups of class I is not affected by the presence of substrates. The alkylation in the presence of tryptophanyladenylate demonstrates that class II is not homogeneous and that the two molecules of adenylate bound to the dimeric enzyme specifically protect two –SH groups out of the four of this class.

Subunit structure of α-acetohydroxy acid isomeroreductase from Salmonella typhimurium

α-Acetohydroxy acid isomeroreductase, purified from Salmonella typhimurium, has a molecular weight of 220,000. The native enzyme consists of a tetramer of four identical subunits on the basis of the following criteria: (1) SDS gel electrophoresis revealed a single component of molecular weight 55,000 (2) carboxypeptidase digestion of the enzyme revealed 4 moles of glycine released per mole of enzyme; (3) amino acid analysis of the native enzyme indicated 204 moles of lysine and arginine; (4) after tryptic digestion, a total of 51 peptides were detected by high voltage electrophoresis and descending chromatography. In the native enzyme, it was possible to tititrate 8 sulfhydryl groups per mole of enzyme. Neither the rate nor extent of sulfhydryl titration was affected by substrates or products. After denaturation with SDS or urea, 8 additional sulfhydryls per mole of enzyme were titrated.

Potentiometric titration of arsenic(III)

Potentiometric redox titration of arsenic(III) in an aqueous solution of hydrochloric acid was studied by the use of a standard potassium iodate solution. The titration curve showed two steps, the first one corresponded to the reaction 5As3++2I5+→5As5++2I0 and the second to the reaction 2As3++I5+→2As5++I+ or 4I0+I5+→5I+. With an increase in the concentration of hydrochloric acid the redox potential in the first stage became higher and the first inflection on the curve was diminished but the second inflection became obvious especially in 36 M acid. On the contrary, with a decrease of the concentration the first inflection became sharp especially in 0.151.5M acid but the second became flat. (Fig. 1) Arsenic could be determined accurately by using one of the two inflections in appropriate concentration of the acid. The reproducibilities were higher than 99.8% for 0.0010.1 M solution of arsenic trioxide. The optimum conditions for the titration were as follows: concentration of hydrochloric acid, 0.151.5M for the first inflection and 35 M for the second inflection; temperature of the solution, 5°C; titration rate at the end point, 0.4 ml per minute.

Regular-insulin doses in monkeys measured by an operant schedule of titrated sucrose reinforcement.

2 adult male squirrel monkeys, Saimiri sciureus, were conditioned on titration schedules of reinforcement which enabled the animals to adjust sucrose concentrations of Noyes 190-mg. food pellets received as reinforcers. Responding on a titration operandum increased available sucrose concentrations by 20% for 30 sec. per titration response. An alternate operandum, which required a response of different topography, produced reinforcers of sucrose concentration determined by titration rate under a FR 30 schedule. Regular insulin, U-40, was administered via the intraperitoneal route in four doses. Highest and lowest doses of insulin resulted in highest sucrose proportion acquired. Intermediate doses resulted in lowest sucrose proportion acquired.

Effects of insulin preparations on titrated sucrose regulation.

Albino rats were conditioned on a titration schedule of reinforcement which enabled the animals to adjust the sucrose concentration of food pellets. Concentrations of 90%, 70%, 50%, 30% and 10% sucrose were decreased by 20% every 30 sec. unless the animal emitted 1 of 2 concurrent operants, which reversed the process. Preparations of globin, protamine, and regular insulins were administered via the intraperitoneal route in small doses, on separate sessions, when steady states on the titration schedule were observed. Regular insulin had the strongest effect in producing higher titration and pellet rates and greater sucrose consumption.

PH stat assay for guanine aminohydrolase

A direct and continuous assay for guanine aminohydrolase has been developed that is based on the liberation of one mole of base for each mole of product formed. Direct continuous titration of the reaction at fixed pH with a standard solution of acid with a pH stat allows one to relate titration rate to rate of product formation. Production of 2 mμmoles of product in a reaction volume as low as 1 ml can be easily measured with results in good agreement with those obtained by the more commonly used procedures.

The determination of sulfur by method of flusk combustion and conductometric titration

An attempt was made to determine of sulfur in organic compounds in one-tenth the scale of the existing microanalytical method. Examination were made on the sample is burnt by the flask incineration method and the amount of sulfate ion formed is determined by titration observing electric conductivity. The volume of titration solution and the effect of titration rate, and the limit of detect were examined by the use of a 2-ml burette. It was thereby found that the determination is possible with samples containing more than 25 μg of sulfur, with good precision comparable to the existing microanalytical method.

Titration of potassium iodide by iodine-cyanide method

Potentiometric titration of potassium iodide with potassium iodate solution by the iodine-cyanide method was studied. The titration curve showed a distinct just corresponding to the reaction I--2e→I+.The optimum conditions for the titration were as follows. Concentration of hydrochloric acid and potassium cyanide at the end point were respectively 11.5M and 0.3M. Temperature was 15°C. Titration rate was 0.2 ml per min. The reproducibilities were higher than 99.6% for 0.140.0028M potassium iodide solution.

CONDITIONS IN SOLUTION DURING THE FORMATION OF GIBBSITE IN DILUTE ALUMINUM SALT SOLUTIONS: III. HYDROXYALUMINUM PRODUCTS OF REACTIONS DURING THE NEUTRALIZATION OF ALUMINUM CHLORIDE SOLUTIONS WITH SODIUM HYDROXIDE

Experiments were made to determine the relative amounts of solid phase hydroxyaluminum to polynuclear ionic hydroxyaluminum formed, according to methods developed by one of the authors, during titrations of dilute AlCl3 solutions with a base. With both 10−3 and 10−2 M AlCl3 solutions, and with both fast (less than 5 minutes) and slow (12 hours) titrations, the solid phase and the polynuclear ions were present at each degree of neutralization at which measurements were made. During the greater part of the titrations the solid phase was the major product with the fast titrations, and the polynuclear ions were the major product with the slow titrations. Beyond about 80% neutralization the polynuclear ions began to decrease in concentration until at 100% the solid phase approached 100% of the products regardless of the rate of titration. There was a considerable amount of Cl associated with the solid phase during most of each titration, but the Cl/Al molar ratio of the solid approached zero as neutralization approached 100%.

Acid-base titration across the membrane system of rat-liver mitochondria. Catalysis by uncouplers.

1. Pulsed acid-base titrations of suspensions of rat-liver mitochondria under anaerobic equilibrium conditions show fast and slow titration processes. 2. The fast process is the titration of the outer aqueous phase of the mitochondria, which is continuous with the suspension medium, and the slow process can be identified with the titration of the inner aqueous phase of the mitochondria, which is separated from the outer aqueous phase by the non-aqueous osmotic barrier or M phase of the cristae membrane system. 3. The buffering power of the outer and inner phases have been separately measured over a range of pH values. 4. The rate of titration of the inner aqueous phase under a known protonmotive force across the M phase has been characterized by an effective proton conductance coefficient, which, near pH7 and at 25 degrees , is only 0.45mumho/cm.(2) of the M-phase membrane. 5. The low effective proton conductance of the M phase will account quantitatively for the observed respiratory control in state 4, assuming that oxidoreduction and phosphorylation are coupled by a circulating proton current as required by the chemi-osmotic hypothesis. 6. The addition of 2,4-dinitrophenol (or carbonyl cyanide p-trifluoromethoxyphenylhydrazone) at normal uncoupling concentrations causes a large increase in the effective proton conductance of the M phase of the cristae membrane. 7. The increase of the effective proton conductance of the M phase by 2,4-dinitrophenol (or carbonyl cyanide p-trifluoromethoxyphenylhydrazone) will account quantitatively for the short-circuiting effect of the uncoupling agent on the proton current and for the observed rise of the rate of respiration to that characteristic of state 3 or higher.

On the reaction between cerium (IV) ions and peroxysulphuric acid

During cerimetric determination of solutions containing hydrogen peroxide and peroxysulfuric acid, the amount of peroxysulfuric acid consumed depends on the rate of titration. Since the same consumption occurs in the absence of hydrogen peroxide, the decomposition must be attributed to the reaction between cerium(IV) ions and peroxyaulfuric acid. Therefore, cerimetric titrations with ceric sulfate and ceric nitrate were investigated. The results showed that in the presence of sulfate ion, the amount of peroxysulfuric acid decomposed in one minute increases proportional to the concentration of Ce/sup 4+/ . The addition of Ce/sup 3+/ to the solution de creases the decomposition as a function of the ratio Ce/sup 4+//Ce/sup 3+/. The reaction between peroxysulfuric acid and Ce/sup 4+/ is more rapid in the presence of nitrate ions than sulfate ions. The reaction rate increases with the addition of Ce/sup 3/. (J.S.R.)