Volumetric iodate method for the determination of thiocyanate

Direct titration of thiocyanate with standard potassium iodate solution is found to yield accurate results in a final hydrochloric acid concentration regulated between 1.5 and 3N. The end-point is determined either potentiometrically or with carbon tetrachloride indicator.     

Mercurous nitrate as a reductimetric reagent: The potentiometric titration of ferric iron in the presence of ions forming highly coloured thiocyanates

The reduction of ferric iron by means of mercurous salts in the presence of an excebs of ammonium, thiocyanate can be predicted on theoretical grounds. By consideration of the oxidation potentials involved it has been shown by calculation that quantitative reduction of the ferric iron is to be expected.—The titration may be effected potentiometrically using a bright platinum indicator electrode in conjunction with a silver/silver chloride electrode or a saturated calomel reference electrode. Ferric iron can be titrated in the presence of ions such as cobalt which form intensely coloured thiocyanate complexes.A possible method for the titration of molybdate by means of mercurous nitrate has been examined. The sensitivity of the method suffers from the instability of potential of the system under titration, but particularly since tungstate does not interfere, the method is worthy of further study.     

Potentiometric argentimetric method for the successive titration of sulphide and dissolved sulphur in polysulphide solutions

Sulphide sulphur and dissolved sulphur in a polysulphide solution can be successively determined with satisfactory accuracy and reproducibility by potentiometric argentimetry in which a sulphide-selective indicator electrode is used. Before the titration, polysulphide ions need to be converted by an excess of potassium cyanide into thiocyanate and sulphide ions. The excess of cyanide ions is masked with formaldehyde and sulphuric acid, then the solution is made alkaline with ammonia and titrated with silver nitrate till the first end-point is reached (sulphide sulphur). After the acidification of the solution with sulphuric acid, the titration is continued till the second end-point is attained (dissolved sulphur).     

Comparison of three electrochemical end-point detection methods to assay potassium dichromate by coulometric titration

Coulometric titrations with three electrochemical end-point detection methods were performed to assay potassium dichromate as a standard for oxidation–reduction titration. The assay as an oxidizing agent was carried out with ferrous ions produced by electrolytically reducing ferric ions. Three end-point detection methods were employed and compared with each other: constant potential amperometry, potentiometry, and constant voltage biamperometry (a dead-stop method). The last one was found to provide high accuracy in the coulometric titration of potassium dichromate. Solution form samples were also measured to confirm the possible existence of chromium(III) in potassium dichromate by both coulometric titration and ion-exchange chromatography with inductively coupled plasma time-of-flight mass spectrometry.     

Simultaneous determination of halide and thiocyanate ions by potentiometric precipitation titration and multivariate calibration

Halide and thiocyanate ions can be determined by a precipitation titration with silver nitrate as the titrant, and the end-point can be evaluated by a potentiometric method, in which generally a silver indicator electrode is used as the indicator electrode and a double-junction Ag–AgCl electrode as the reference electrode. However, when mixtures of halide and thiocyanate are titrated, it is difficult to determine these components individually for there are overlapping steps in the potentiometric titration curves, especially in the case that there are obvious differences between concentrations of the components. In this paper, the linear equation for the potentiometric precipitation titration of a mixture of halide and thiocyanate ions was developed and it was then used for determining the components in the mixtures simultaneously with the aid of multivariate calibration methods. By application of this model, 27 synthetic mixtures with three- and four-component combinations of chloride, bromide, iodide and thiocyanate with low concentration levels from 1.8×10⁻⁴ to 6.2×10⁻⁴ mol l⁻¹ were analyzed and acceptable results were obtained.     

Sodium meta-vanadate as volumetric reagent: Iodine monochloride method

In hydrochloric acid medium sodium meta-vanadate was used as a volumetric reagent for the determination of copper, zinc, cobalt, mercury, and lead. Cu⁺², Zn⁺² and Co⁺²were precipitated as complex mercurythiocyanates, Hg⁺² as mercuric zinc thiocyanate and Pb⁺² as Iodide. The thiocyanates were dissolved in concentrated hydrochloric acid and titrated against standard sodium meta-vanadate solution in the presence of iodine monochloride as a pie.oxidizer and catalyst. In titration of the iodide against the meta-vanadate. it was not necessary to add iodine monochloride to the titrant because it is formed during the titration. Chloroform was used as an indicator. It was pink owing to the liberation of iodine during the titration and became pale yellow at the end-point because of the formation of iodine monochlonde.     

滴定分析的终点误差随待测物浓度及反应平衡常数单调变化之商榷

为了获得滴定分析的终点误差随待测物浓度、反应平衡常数这两个因素变化的准确规律,推导了有别于林邦终点误差公式的终点误差计算式,根据该式可以判断每个因素对计算结果的影响,结合在配位滴定分析和酸碱滴定分析的具体应用,结果发现：这两个因素其大小的变化不会一定导致终点误差绝对值的单调变化。     

Mercurous nitrate as a reductimetric reagent : The determination of copper

It has been found that in the presence of excess thiocyanate ions, cupric copper will oxidise ferrous ions. Use has been made of this reaction to determine copper by titration of the ferric iron produced, with mercurous nitrate. Although this reaction is the reverse of that usually observed, where the cuprous ion reduces the ferric iron, it has been found that the large excess of thiocyanate is responsible for this effect.     

Photometric titration of iron with ethylenediaminedi(o-hydroxyphenylacetic acid)

Fractional mg quantities of ferric iron in 100 ml of solution can be titrated at PH 3.5 with a solution of ethylenediaminedi(o-hydroxyphenylacetic acid). The end-point is found photo- metrically. Errors are generally under 1%, and a number of metals do not interfere. By scaling down the volume of the solution and the titrant concentration, the titration can be extended to μg quantities of iron, and mg quantities are also accessible by changing to a wave length where the sensitivity is not so great. The titration may be useful in certain applications.     

Die jodometrische bestimmung von eisen und kupfer

In cases where many titrations have not to be carried out or where the cost of the reagents may be ignored, it is proposed to employ, for a single determination of 2–3 mval Cu (equivalent to 20–30 ml $\text{N}\text{10}$ thiosulphate), 5 g of solid potassium iodide ; the cuprous iodide remains at first in solution as a complex and finally produces a slight white precipitate. The end-point of the titration is clearer than in the usual method. If a neutral concentrated solution of ferric chloride is added to a small amount of the catalyst, potassium cuprous iodide, prepared as above, it is possible to titrate immediately and accurately the equivalent quantity of iodine which is released.By this procedure a considerable economy of time and increased precision of the titration of copper and iron may be realized.     

Determination of iron in the presence of large amounts of phosphate by titration with disodium dihydrogen ethylenediaminetetraacetate

Ferric iron, even in the presence of comparatively large amounts of phosphate, can be determined by titrating with the disodium salt of ethylenediaminetetraacetic acid (Versenate, Complexone III), using ammonium thiocyanate as indicator and extracting the red ferric thiocyanate into amyl alcohol, provided the pH is controlled at 2.0—2.4 at the end-point. The method has been successfully used for the determination of iron in phosphate-containing deposits from steam boilers.     

Mechanism and reaction rate of the karl fischer titration reaction: Part V. Analytical Implications

The Karl Fischer titration procedure for the determination of water has been studied. In view of the results of previous investigations, a methanolic sodium acetate—sulfur dioxide solution is recommended as solvent and an iodine solution in methanol as titrant. The advantages of this procedure over a conventional Karl Fischer titration are: a much more rapidly reacting reagent, the possibility of a visual end-point detection, a titrant of constant titre over a long period of time, and the absence of the disagreeable odour of pyridine.     

Complex formation and fluorescence: 8-Quinolinol-5-sulfon1c acid as a titrant for bivalient cations

8-Quinolinol-5-sulfonic acid can be used in compleximetric titrations by means of a displacement type of titration; a fluorescent weak complex is used to titrate an ion which forms a non-fluorescing stronger complex, the end-point being the appearance of fluorescence. The titration is best performed by an instrumental method. A non-fluorescing weak complex can similarily be used for the titration of a cation which is strongly complexed and fluoresces. By making use of suitable combinations, it is possible to titrate a non-fluorescing complex former and a fluorescing complex former in the same solution.     

Ferrimetric determination of uranium using rhodamine 6G as fluorescent indicator

Experimental conditions have been developed for the titration of uranium^IV with iron^III alum solution, using Rhodamine 6G as a fluorescent indicator. The titration is best carried out at 98–100° in a 2–3N hydrochloric acid medium, under filtered ultraviolet light, using 2.0 ml of 0.05% Rhodamine 6G solution for 30 ml of the titration mixture. A slight excess of iron^III solution quenches the greenish-yellow fluorescence of the dye through inner filter action. With the titration assembly described here, it is possible to determine uranium^IV with an accuracy of about 0.4%. This method appears to be more convenient than the potentiometric titration or the method employing potassium thiocyanate as internal indicator.

Evidence is also presented to show that the reaction between uranium^IV and iron^III is slow at room temperature.     

Tris(4,7-dihydroxy-1,10-phenanthroline)iron(II) as a low-potential oxidation-reduction indicator: determination of hydrosulphite

The formal reduction potential of the tris(4,7-dihydroxy-1,10-phenanthroline)iron(III,II) couple is -0.06 V in the pH range 10-13, not -0.11 V as reported earlier. The couple forms an excellent visual oxidation-reduction indicator for the titration of sodium hydrosulphite with potassium ferricyanide in alkaline solution.     

Coulometric titration of antimony with electrogenerated iodine

A method is described for the coulometric titration of tripositive antimony with electrogenerated iodine, in a buffered solution of pH 8. The end-point can be detected either amperometrically, potontiometrically, or (less precisely) visually with starch indicator. Quantities of antimony between 0.06 and 10 mg are titratable with an average error of 0.001 to 0.01 mg.     

Volumetric studies in oxidation-reduction reactions: Oxidation with chloramine-t. iodine monochloride method

Chloramine-T has been used as an oxidizing agent in hydrochloric acid medium' for the volumetric estimations of potassium iodide, hydrazine sulphate, arscnious oxide, stannous chloride, mercurous chloride, tartar-emetic, potassium thiocyanate and ferrous ammonium sulphate, using iodine monochloride as a catalyst and pre-oxidizer. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes very pale yellow at the end-point because of the formation of iodine monochloride.     

The heterometric microdetermination of mercury of mercaptobenzthiazole

The heterometric determinations of murcury or mercaptobentlnazole are very sensitive reactions. An aqueous or a dilute alcoholic solution is used and the titration may lie carried out at pH 2–10. If meicaptobenzlhiazole is determined, two analytical end-points are obtained : the first gives an estimate, the second gives the precise end-point. In all cases, the insoluble Hg(MBT)₂ is obtained, The presence of larger amounts of strong acids is disadvantageous Large amounts of acetic acid cause distuibances in aqueous solution; dilute alcoholic .solution is therefore used The theoretical end-point is obtained by the intersection of two lines. In acid solution a horizontal maximum density line is obtained at the end ot the reaction, in alkahne solution a maximum point is obtained instead. 1–2 mg mercury or meicaptobenzthiazole may be determined in 20–30 ml solution with an error of 0–3% 'Ihe titration time is 10–20 mniutes     

Studies in bivalent chromium salts

Summary As shown in the above investigations, chromous sulphate can be used for the quantitative reduction of compounds containing nitro, nitroso, quinoid, and azo groups. In the case of the first three, the estimations can be carried out by either of the two methods, direct titration by using neutral red, phenosafranine orp-ethoxychrysoidine as internal indicators, or by adding excess of chromous sulphate and titrating the excess with ferric solution, using thiocyanate as indicator. The comparative study of reduction of azodyes shows that the dyes can be estimated quantitatively with chromous sulphate as well. It is also possible to estimate the carbohydrates, since the unused copper sulphate can be directly titrated against chromous sulphate in presence of neutral red or phenosafranine as indicator. The results are fairly satisfactory and within experimental error (± 0.9°/0).The author is highly indebted to Dr. R. C. Mehrotra, Professor of Chemistry, Gorakhpur University, for his helpful suggestions and keen interest in the work.Part VII: See. Z. analyt. Chem. 164, 314 (1958).     

Analysis of sulphonyl chlorides by polarovoltric titration with sodium sulphide

A method has been developed for the rapid analysis of aliphatic and aromatic sulphonyl chlorides by polarovoltric titration with a standardised sodium sulphide solution. Visual end-point determination is also possible in more concentrated solution.