Iodate iodometric titration

A simple and rapid method for the iodometric determination of microgram amounts of chromium(ni) in organic chelates is based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the umeacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate . Iodometric titration was also used for determination of the effective isoascorbate (see 2) concentration in fermentation processes . The content of calcium ascorbate can be determined with high sensitivity by complexometric titration with edta, which is superior to iodometry. The purity of /3 -diketonate complexes of Al, Ga, In and Ni was determined by complexometric titration with edta at pH 5.5-3, with RSD < 0.01 for determining 5-30% metal ion. Good analytical results were obtained by a similar procedure for the metal content of 15 lanthanide organic complexes. ... 

Iodine was determined by an iodometric titration adapted from White and Secor.(3) Instead of the normal Carius combustion, iodide was separated from the samples either by slurrying in 6M NaOH, or by stirring the sample with liquid sodium-potassium (NaK) alloy, followed by dissolving excess NaK in ethanol. Precipitated plutonium hydroxides were filtered. Iodine was determined in the filtrate by bromine oxidation to iodate in an acetate buffer solution, destruction of the excess bromine with formic acid, acidifying with SO, addition of excess KI solution, and titrating the liberated iodine with standard sodium thiosulfate. The precision of the iodine determination is estimated to be about 5% of the measured value, principally due to incomplete extraction of iodine from the sample. 

The practical application of these observations is to minimise the effect of iodate by rapidly carrying out the iodometric titration of chlorine residual in seawater at pH 4. Moreover, if desired, a titration correction curve can be generated using iodate at the specific concentration of iodide in the sample in question, as there appears to be a complete conversion of seawater iodide to iodate in the presence of excess chlorine. 

Chlorine gas may be identified readdy by its distinctive color and odor. Its odor is perceptible at 3 ppm concentration in air. Chlorine may be measured in water at low ppm by various titrimetry or colorimetric techniques (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington DC American Pubhc Health Association). In iodometric titrations aqueous samples are acidified with acetic acid followed by addition of potassium iodide. Dissolved chlorine liberates iodine which is titrated with a standard solution of sodium thiosulfate using starch indicator. At the endpoint of titration, the blue color of the starch solution disappears. Alternatively, a standardized solution of a reducing agent, such as thiosulfate or phenylarsine oxide, is added in excess to chlorinated water and the unreacted reductant is then back titrated against a standard solution of iodine or potassium iodate. In amperometric titration, which has a lower detection limit, the free chlorine is titrated against phenyl arsine oxide at a pH between 6.5 and 7.5. 

Potassium iodate is an oxiding agent in volumetric analysis. It releases iodine in KIO3-KI solutions for iodometric titrations. It also is a topical antiseptic and an additive to food to provide nutrient iodine. 

The direct Ripper iodometric titration is still used, but it is subject to error. In its place, direct iodate-iodide titration is used (44). This is followed by fixing the sulfur dioxide with glyoxal in a second sample and retitrating. The difference represents the free sulfur dioxide. The second titration roughly represents the amount of reduction and the amount of ascorbic acid present. Formulas for calculating the amount of sulfur dioxide to add in order to produce a predetermined level of free sulfur dioxide have been given by Stanescu (45). 

The addition of excess calcium acetate to purified cellulosic material suspended in water, followed by titration of the liberated acetic acid, was suggested by L(idtke. From the 0.1% carboxyl content obtained, a D.P. value of 277 was calculated for the cellulosic material employed. This method has been studied further and comparative data with the earlier conductometric titration procedure have been presented by Heymann and Rabinov, by Kenyon and coworkers, and by Sookne and Harris. The latter workers report that electrodialyzed depectin-ized cotton has a carboxyl content of 0.045% or a D.P, of 616. An iodometric titration procedure for estimating carboxyl groups in cellulosic materials has also been described by Ltidtke. The procedure involves a thiosulfate titration of the iodine liberated from a mixture of potassium iodate and potassium iodide by the carboxyl groups of the cellulosic material. The carboxyl content determined by this method agreed well with that obtained by the calcium acetate method. 

Colourimetric modifications of iodometric titration methods (see Section 6.2.1) have been reported in which the excess iodine is determined at 520nm after reaction with metol and sulphanilamide [86] or in which iodine liberated by reaction of the penicilloic acid with potassium iodate is measured at 520nm [87]. These methods should retain the high specificity of the titration procedures. 

Triphenylphosphine, triphenylarsine, and trip-henylstibine can be amplified by oxidation with periodate in acidic or alkaline medium and iodometric titration of the iodate ion released. Two reaction routes (reactions [XII] and [XIII]) can be employed, where Z = P, As, or Sb ... 

Bromination of organic compounds and subsequent reaction with iodide provides an indirect amplification based on the extraction of the iodine liberated, reduction to iodide, and iodometric titration of the iodate formed by Scheme 1. By this method phenol is ampfified 12 times and resorcinal and phloroglucinol 24 times. Other compounds, such as sahcylic acid, acetylsalicylic acid, and p-hydro-xybenzoic acid, have been also amplified. 

Procedure (iodometric method). Weigh out accurately about 5.0 g of the bleaching powder into a clean glass mortar. Add a little water, and rub the mixture to a smooth paste. Add a little more water, triturate with the pestle, allow the mixture to settle, and pour off the milky liquid into a 500 mL graduated flask. Grind the residue with a little more water, and repeat the operation until the whole of the sample has been transferred to the flask either in solution or in a state of very fine suspension, and the mortar washed quite clean. The flask is then filled to the mark with distilled water, well shaken, and 50.0 mL of the turbid liquid immediately withdrawn with a pipette. This is transferred to a 250 mL conical flask, 25 mL of water added, followed by 2 g of iodate-free potassium iodide (or 20 mL of a 10 per cent solution) and 10 mL of glacial acetic acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate. 

For the use of the iodometric method in the analysis of mixtures containing sulphide, sulphite and thiosulphate, see Kurtenacker and others, Zeitsch. an.org. Chem., 1924, 141, 297 1927, 161, 201 and for mixtures of sulphide, polysulphide and thiosulphate, see Sohulek, Zeitsch. anal. Chem., 1925, 65, 352. For titration methods using potassium iodate, see Jamieson, Amer. J. Sci., 1915, 39, 639 also Ivanofi, J. Buss. Phys. Chem. Soc., 1914, 46, 419 Dimitrow, Zeitsch. anorg. Chem., 1924, 136, 189. 

Two iodine based methods have been published for amoxicillin and other penicillins which claim an exact stoicheiometry so that a reference standard is not required. In one [62] the penicilloic acid was reacted with potassium iodate at pH 5 and the liberated iodine titrated. A sample blank could be carried out as in the conventional iodometric method. In the other [63], the penicillin in 10% HC1 was reacted with iodoxybenzoate, potassium iodide added and the released iodine titrated. The same group had previously claimed exact stoicheiometry for a method in which amoxicillin in 10% HC1 was titrated with dibromodimethylhydantoin [64]. Both these methods were based on oxidation of products of penicillin degradation in the strong acid conditions. No information was provided about possible interference by potential impurities and the conditions are such that inclusion of a sample blank seems to be impossible. 

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