Titrations iodimetric

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

Iodimetric titration, 23 670-671, 676 Iodination, 22 274 Iodination reaction, 9 281 23 649 Iodine (I), 24 353-380. See also Blend iodine value 131I isotope analytical methods for, 24 367-368 catalyst poison, 5 257t... 

How would you assay the following drags by iodimetric titrations ... 

Analytical Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. Iodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being determined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by liquid chromatography (366). 

In the iodimetric titration procedure, the combustion gases are bubbled through a diluent solution containing pyridine, methanol, and water. This solution is titrated with a titrant containing iodine in a pyridine, methanol, and water solution. In automated systems, the titrant is delivered automatically from a calibrated burette syringe and the endpoint detected amperometrically. The method is empirical, and standard reference materials with sulfur percentages in the range of the samples to be analyzed should be used to calibrate the instrument before use. Alternative formulations for the diluent and titrant may be used in this method to the extent that they can be demonstrated to yield equivalent results. 

The solution may be conveniently analyzed by the addition of excess potassium iodide followed by an iodimetric titration. The stoichiometry of the reaction is ... 

Specifications for ascorbic acid, sodium ascorbate, calcium ascorbate, and ascorbyl palmitate are found in the UnitedSfates Pharmacopeia/NationalFormu/a (71) and the Food Chemicals Codex (72). The official assay for all four compounds is the iodimetric titration with 0.1 iodine solution and starch as the indicator. 

The method (16) describes the titrimetric microdetermination of salicylic acid, aspirin and p-hydroxybenzoic acid by amplification reactions. The cited acids are brominated with Br to form tribromophenyl hypobromite, which after removal of unconsumed Br wtih formic acid, is treated with iodide to give tribromophenol and free iodine. The liberated iodine is extracted with CHCI3 and reduced to iodide, which is determined by oxidation with Br and iodimetric titration of the iodate produced with Na2S203 solution. This six fold amplification... 

Preparation. One standardized proeedure involves disproportionation of iodosobenzene. A thin paste of 110 g. of iodosobenzene in water is steam distilled in a 5-1. flask untQ removal of iodobenzene is complete the recovery of pure halide is about 90%. The hot mixture is cooled and the white solid is collected, dried, and ground in a mortar. The purity as determined by iodimetric titration is 99%. 

The extract is washed with ammonium sulfate solution, dried, and hitered. The solution is used directly for an epoxidation or other reaction. The yield cited is based upon iodimetric titration. 

The estimation of thebaine in the analysis of opium is described by Klyachkina [55] and Anneler [56], The alkaloid has been estimated in opium residues by condensation with benzoquinone, isolation of the very sparingly soluble adduct, and iodimetric titration of this in chloroform solution. This method is reported to be accurate to 0-5 per cent., provided resins, dyeing substances, and phenolic alkaloids are first removed [57]. Thebaine can also be estimated as its silicotungstate [53] or salicylate [54]. 

The thebaine content of opium residues has been determined by treatment of the residues with benzoquinone, isolation of the adduct, and iodimetric titration of the latter in chloroform [7]. 

Challenge Problem. Verdini and Lagier developed an iodimetric titration procedure for determining ascorbic acid in vegetables and fruits. They compared the results of their titration experiments with similar results from an HPLC method... 

Colour transitions of indicators Acid-alkali and iodometric/iodimetric titration Pipetting technique... 

The reactor held one liter of 0.1 M CaCl2 solution. Buffers were added in nominal concentrations as needed. The pH was adjusted to the desired value by adding HC1 or NaOH. The experiment was initiated by addition of 0.5 g of Fisher Reagent CaC03 (precipitated calcite). In runs with sulfite the reactor solution was analyzed by iodimetric titration before and after the experiment. 

Why are iodimetric titrations usually done in neutral solution and iodometric titrations in acid solution ... 

The simplest method available for the determination of sulfur dioxide in foods is iodimetric titration in the presence of starch after addition of acetone, glyoxal, or formaldehyde. Acidification before the titration allows the determination of both free and reversibly bound sulfur dioxide. Amperometric methods for detecting the endpoint allow the method to be extended to colored samples. 

A long-established procedure for the determination of sulfur dioxide is the Monier-Williams method in which sulfur dioxide is distilled from an acidified solution and the vapor passes through U-tubes containing hydrogen peroxide which oxidizes it to sulfuric acid. The acidity produced is then titrated with dilute standard alkali. This procedure is preferred to an iodimetric titration when volatile sulfur compounds are present as in mustard, onion, and horseradish. Sulfur dioxide may also be... 

Titmetric and colorimetric methods are available for the determination of aldehyde contents in alcoholic beverages. An iodimetric method has been used for the determination of the total aldehyde content of wines. A modified iodimetric titration method is included in the methods of AOAC. In order to avoid the reactions of interfering substances, aldehydes are separated by distilling an aliquot of wine into a neutral hydrogensulfite solution. After the excess of hy-drogensulfite has been titrated with an iodine solution at pH 2, hydrogensulfite is released from its aldehyde addition compound at pH 9 and titrated with iodine solution. 

Though iodimetric titration of iron (III), which involves the reaction of iron (III) with acidified iodide and titration of the liberated iodine with standard thiosulphate, has been recommended in British Pharmacopoeia, 1968, the most frequent [20] difficulties are encountered due to recurring end-points, as the reaction is very slow near the stoichiometric end-point. Extraction of the liberated iodine into chloroform or carbon tetrachloride has been recommended to push the reaction to completion [20]. However, such titrations involving two immiscible phases are always cumbersome and the endpoint is often carried over. 

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