Determination of thioacetamide by oxidation with chloramine-T

Chloramine-T oxidises thioacetamide quantitatively in an alkaline medium in the hot, converting the entire sulphur into sulphate. A back-titration method, making use of this oxidation reaction, has been suggested for the determination of thioacetamide.     

The titration error in potentiometric precipitation titration

The titration error can be calculated with the aid of the value of the buffer index determined at the inflection point of the titration curve when a precipitation titration is followed with an ion-selective electrode. When the precipitate is not formed ideally in the titration (i.e., is not formed under equilibrium conditions) the titration error cannot be predicted from the values of the solubility product, nor can the values of the solubility product be calculated from titration data at the inflection point.     

Highly stereoselective C-allylation of an enantiopure alpha-sulfinyl thioacetamide

The alkylation of the lithium enolate of enantiopure alpha-cyclohexylsulfinyl thioacetamide 1 with allyl bromides 5 possessing an electron-withdrawing group at the vinylic position does not occur at the sulfur center - as expected in the sulfur series - but at the carbon center through conjugate addition followed by bromide elimination. The modest to excellent 1,2-asymmetric induction achieved by the alkylsulfinyl group (dr up to 100:0) is explained by an electronic model.     

Amperometric argentimetric and mercurimetric titration of sulfhydryl: Mercurimetric titration

The ampero-mercurimetric titration of cysteine (RSH), glutathione (GSH), thioglycolic acid (TSH) and 2-mercaptoethanol (ESH) at the RMPE at pH 9 yields a sharply defined end-point corresponding to the composition (XS)₂Hg. Under the same conditions with the KPtWK two lirciiks an; (ibst'rvc-d in the titration lines with RSH and GSH, corresponding to compositions (RS)₂Hg and (RS)₂Hg₂ respectively. On the other hand, with TSHl and ESH only one clear break is found at the RPtWE corresponding to ('l'S)₂Hg or (ES)₂Hg Conditions liave been describcd for the accurate mercurimetric titration of the thiol compnunds at pH 2 in the pesence of 0.01 M sulfur dioxide at the RMPE, use of this can be made in the determination of disufides and in the determination of the equilibrium concentrations of the reaction betwcen a disulfide and a sulfite at varying pH.     

Precipitation of zinc sulfide by the hydrolysis of thioacetamide

Zinc can be precipitated quantitavely as zinc sulphide using thioacetamide in a weakly acid solution. This is accomplished by carrying out the reaction in a sealed tube at 120⁰. The method, however, does not give a good separation from cobalt. Best separations are obtained by using a sulfate-bisulfate buffer containing ammonium thiocyanate with hydrogen sulfide as precipitant.     

Amperometric determination of thioacetamide with copper(I)

A method is given for the amperometric determination of thioacetamide (TAA) based on the reaction of TAA with copper(I) in ammoniacal solution. The reduction current due to the copper(I) is used to determine the end-point. The determination is carried out at constant temperature (25°), pH 8.0-9.8 (ammonia-urotropine buffer), and at constant potential (−0.6 V vs. S.C.E.), with a dropping mercury electrode as cathode and a saturated calomel electrode as anode. The solution is deaerated by a stream of electrolytically generated hydrogen. The titrations are carried out simply and rapidly and the results are fairly reproducible. The error is generally 1.0% for amounts of TAA ranging from 0.07 to 1.8 mg.     

Amperometric argentimetric and mercurimetric titration of sulfhydryl: Argentimetric titration

Results of amperometric argentimetric titrations at the rotated platinum wire electrode in ammonia buffers of cysteine, glutathione, thioglycolic acid and 2-mercaptoethanol are presented. The method gives satisfactory results with glutathione and 2-mercaptoethanol. Thioglycolic acid gives good results in the presence of sulfite but high results in its absence. Its disulfide can be titrated accurately in the presence of sulfite. In agreement with other workers it was found that cysteine yields high results. The error increases with increasing cysteine concentration and is reduced in the presence of 0.1 M sulfite. It becomes equal to zero at cysteine concentrations equal to or smaller than 5.10^-5M.     

Voltammetric study of copper(I) thioacetamide complexes

Summary The composition and stability of copper(I) complexes with thioacetamide (TAA) have been evaluated with the help of square-wave voltammetry using the fast pulse technique. Two species, namely Cu(I) (TAA) and Cu(I) (TAA)₂, have been identified having the formation constants log ₁=16.85; log ₂=18.03. The complex is stable in highly acidic medium (pH1). The application for the determination of copper is pointed out.     

Microcomputer-aided high-speed potentiometric titration system by linear titration plots

Summary An apparatus for high-speed potentiometric titration was assembled and its advantage was demonstrated. Titrant additions were made stepwise in large volumes. The optimum increment volumes were automatically chosen by microcomputer, depending upon the sample concentration. Time intervals between the successive additions were controlled so as to add a new increment immediately after the electrode was equilibrated. On-line calculation of the equivalence volume was conducted based upon linear titration plots, using only four titration points before the equivalence point. The apparatus was capable of determining the concentration of strong and weak monoprotic acids in less than 22s with relative standard deviations of 0.1–0.2%.

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Potentiometrisches Titrationssystem hoher Geschwindigkeit, das auf linearen Titrationskurven beruht und mit einem Mikrocomputer arbeitet

Zusammenfassung Der Aufbau des Geräts wird beschrieben und seine Vorzüge werden diskutiert. Die Zugabe des Titrationsmittels erfolgt stufenweise in großen Anteilen. Die optimalen Volumina werden automatisch je nach Konzentration von einem Mikrocomputer bestimmt. Die Zeitintervalle zwischen den Zugaben werden so gesteuert, daß jeweils nach Gleichgewichtseinstellung der Elektrode eine neue Zugabe erfolgt. Aufgrund linearer Eichkurven erfolgt die online Berechnung des Äquivalenzvolumens, wobei nur vier Titrationspunkte vor dem Äquivalenzpunkt verwendet werden. Mit Hilfe des Gerätes können starke und schwache monoprotische Säuren in weniger als 22 s mit einer relativen Standardabweichung von 0,1–0,2% bestimmt werden.

     

Calibration of titration methods

Summary A calibration method is proposed which makes it possible to use titration techniques in the presence of systematic errors, even if these errors depend on the concentrations of the analytes. The approach uses an empirical calibration model which approximates the relationship between apparent (found) and true concentrations of the analytes. Also a calibration of the physical model of the titration process is proposed, as well as a method of determination of the model parameters, which are useful when analytes are determined by fitting the model to experimental data of titration. Both approaches, empirical and based on the physical model, may be applied jointly. The example presented reveals high efficiency of the proposed approach in cases when a deficient physicochemical model of the titration process is used in the determination of an analyte concentration (simulated titration data applied). The calibration proposed may be considered as a generalization of the titrant standardization used in the conventional volumetric analysis. It may be applied to all titration techniques and for all methods of end-point detection and determination of the concentration of analytes. It opens new possibilities for the development of titration methods. Permanent address: Department of Analytical Chemistry, Jagiellonian University, Karasia 3, PL-30-060 Krakow, Poland     

Modified titration of potassium

A simplified titrimetric method for potassium is proposed. In the usual method, potassium is precipitated by sodium tetraphenylborate and the excess of the reagent is back-titrated with a quaternary ammonium salt, but the precipitate must be removed to prevent the reaction between the precipitate and the titrant. Polyvinylpyrrolidone can be used to deactivate the precipitate so that it need not be removed.     

Wollack titration of thiosulphate

The Wollack titration for the determination of thiosulphate has been reinvestigated. Various modifications are proposed and the conditions necessary for satisfactory results are discussed.     

Complexometric titration of Aluminium

A procedure is given for the complexometric titration of aluminium. A known volume of a standard solution of EDTA is added to the sample solution, and the excess is back-titrated with a zinc sulphate solution, dithizone being used as indicator. The titration is performed at pH = 4.0 — 4.5 and 40 — 50% alcohol is added as solvent for the indicator.The theoretical basis of the method is developed, and the theoretical titration error with various amounts of aluminium and zinc is calculated.The results of some titrations are given.     

Amperometric titration of molybdenum

A method for the amperometric titration of molybdenum(Vl) with lead nitrate solution is described. The precipitation is carried out at room temperature from an acid sodium acetatepotassium chloride supporting electrolyte. The diffusion currents are recorded at a potential of —0.8 V vs. S.C.E. where both the lead and molybdenum give reduction waves. While the reduction of molybdenum in acetic acid buffer produces no well defined plateau, it gives accurate and reproducible results amperometrically. The analytical precision is about 0.4%.     

Thermometric titration of sulphate

Direct thermometric titration of sulphate with a solution of barium perchlorate is proposed. The stoichiometry of the titration is shown to be critically dependent on the concentration of ethanol in the titration medium. The titration is rapid and suffers from only a few interferences.     

Potentiometric titration of plutonium

In the potentiometric titration of plutonium(III), it has been customary to take the equivalence point as the inflection point on a plot of potential vs. volume of titrant.¹ That the stoichiometric end point corresponds to the inflection point does not seem to have been theoretically demonstrated, however. The purpose of this letter is to suggest that these points may not correspond in the potentiometric titration of plutonium(III). Mound Laboratory is operated by Monsanto Research Corporation for USERDA under contract No. EY-76-C-04-0053.