Iodometric titration methods

The direct iodometric titration method (sometimes termed iodimetry) refers to titrations with a standard solution of iodine. The indirect iodometric titration method (sometimes termed iodometry) deals with the titration of iodine liberated in chemical reactions. The normal reduction potential of the reversible system ... 

The preferred method for analyzing chlorinated isocyanuric acids and their salts is the iodometric titration (J) The main limitation of the iodometric titration method is sample size generally one would need a minimum of 100 milligrams for titrating either compound. For industrial hygiene samples, this is a problem because sample weights are usually smaller by a factor of 20,... 

Test Method for Sulfur in Graphite by Combustion—Iodometric Titration Method... 

International Standard Organization. 1990. Water quality. Determination of free chlorine and total chlorine. Part 3 Iodometric titration method for the determination of total chlorine. ISO 7393-3. International Organization for Standardization, Case Postale 56, CH-1211, Geneva 20 Switzerland. 

Iodometric Titration Method Iodometric titration assay, which is based on the oxidation of the iodide ion (1 ) by hydroperoxides (ROOH), is the basis of current standard methods for determination of PV (9). In this method, a samrated solution of potassium iodide is added to oil samples to react with hydroperoxides. The liberated iodine (I2) is then titrated with a standardized solution of sodium thiosulfate and starch as an endpoint indicator (7, 9, 20). The PV is obtained by calculation and reported as milliequivalents of oxygen per kilogram of sample (meq/kg). The official determination is described by lUPAC (21). Chemical reactions involved are given below ... 

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. 

The sterol content in lipids was determined spectrophotometrically at 625 nm wavelength by method described in [13], Serva Company (ERG) cholesterol was used for plopping the calibration curve. The spectrophoto-metrical measurements were carried out on a KFK-3 device (Russia). The content of diene conjugates (DC) and ketodienes (KD) was determined by UV-photometry from the ratio of the optical density of the lipid solution in hexane (0.05-0.3 mg/ml) at 230 2 nm and 270 2 nm to 205 2 nm wavelengths respectively, using a spectrophotometer Shimadzu UV 3101 PC (Japan). The peroxide content in lipids was determined by the current iodometric titration method. The antiperoxide activity (APA) of lipids, i.e., the ability of lipids to decompose peroxides, was assessed by the ratio of the difference in the concentrations of peroxides in the oxidized methyl oleate and in the lipid solution in this methyl oleate to the amount of the added lipids [3]. 

In order to determine the methods of glutathione assay currently in use, a survey was made of the literature during the five-year period between 1948 and 1952. During this period approximately 300 papers on glutathione were published. It was possible to obtain about two thirds of these for study. Over half of the papers described the use of glutathione and were not concerned with assay. Glutathione determinations were made in 85 cases (Fig. 1). The iodometric titration method was used in almost half... 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

Kupec et al. [180] determined total sulphur in sludge by a method involving magnesium reduction in which the sample is heated with magnesium powder to convert all sulphur compounds into magnesium sulphide. The magnesium sulphide is treated with sulphuric acid and the evolved hydrogen sulphide determined by iodometric titration. 

These iodometric calibration methods are based on the assumption that there is a stoichiometric reaction between ozone and the iodine in the various potassium iodide procedures. Three essentially independent methods have been used to test the accuracy of this assumption measuring the absorption of ultraviolet radiation at 254 nm by ozone in air, measuring the absorption of infrared radiation at 9,480 nm by ozone in air, and determining the ozone concentration in air by titration with nitric oxide. 

APHA Method 4500-CL02-B, iodometric titration analysis, measures the concentration of chlorine dioxide in water by titration with iodide, which is reduced to form iodine. Iodine is then measured colorimetrically when a blue color forms from the production of a starch-iodine complex. The detection limit for this method is 20 pg/L (APHA 1998). 

Elemental composition, A1 10.11% and Br 89.89% A1 analyzed by AA spectrophotometry or colorimetric methods Br analyzed by iodometric titration or ion chromatography and then calculated stoichiometrically solid may be dissolved in an organic solvent and determined by GC/MS, identified by mass ions (AlBr3 )n where n is 2, 4 and 6. 

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. 

Titrimetric methods also measure gold in solution. Gold(llI) may be reduced by excess hydroquinone which may be back titrated with a standard solution of cerium(lV) titrant. (4old(lll) may also be determined by iodometric titration. 

Hydrazine may be analyzed by various methods including GC-FID, GC-NPD, HPLC, GC/MS, polarography, colorimetry, and iodometric titrations. The iodometric method is simple and apphcable to measure hydrazine quantitatively in water at aU concentrations. 

Oxygen difluoride may be analyzed by GC, GC/MS, IR, and NMR methods. The compound may be identified by GC/MS, the characteristic mass ions are 54, 38 and 35. The compound can be measured quantitatively by wet methods based on its strong oxidizing ability (see Reactions). It liberates I2 from an acidified solution of potassium iodide and the liberated I2 can be measured by iodometric titration using Na2S20s titrant and starch indicator. Alternatively, the compound may he treated with a measured amount of excess NaOH and the unreacted excess NaOH measured hy titrating against a standard solution of HCl. Also, the fluoride ion, F, may he measured by fluoride selective electrode. 

Elemental composition Na 58.93%, S 41.07%. An aqueous solution is analyzed to determine sodium content. Also, an aqueous solution may be analyzed for sulfide by methylene blue colorimetric test or by iodometric titration (APHA, AWWA, and WEF. 1999. Standard methods for the Examination of Water and Wastewater, 20 ed. Washington, DC American Pubhc Health Association). The methylene blue test is based on reacting sulfide, ferric chloride and dimethyl-p-phenylenediamine to produce methylene blue. Also, sulfide can be measured by using a sdver-sdver sulfide electrode. Quahtatively, sulfide may be identified from the hberation of H2S on treatment with acid. The H2S turns the color of paper soaked with lead acetate black (See Hydrogen Sulfide). 

It was proposed to replace the final titration of Is in the standard method with a redox potentiometric method, which is less laborious, fast and prone to automation. The LOD is 0.16 meqkg, allowing determination of POV in fresh oil. A method based on the potentiometric determination of the equilibrium in equation 54, in aqueous solution containing a large excess of I, with a Pt electrode vs. SCSE, was proposed to replace the standard iodometric titrations of Section IV.B.2 for determination of the POV of oils. The proposed method is fit for purpose, based on the measurement uncertainties, as compared to those of the standards based on iodine titration with thiosulfate solution. The analytical quality of the potentiometric method is similar to that of the standards based on titrations for oils with POV >0.5 meqkg however, for fresh oils, with much lower POV, the potentiometric method is bettef . 

In solutions, the concentration of available chlorine in the form of hypochlorite or hypochlorous acid is called free-available chlorine. The available chlorine in the form of undissociated IV-chloro compounds is called combined-available chlorine. Several analytical methods can be used to distinguish between free- and combined-available chlorine (8). Bleaches that do not form hypochlorite in solution like chlorine dioxide and nonchlorine bleaches can be characterized by their equivalent available chlorine content. This can be calculated from equation 5 by substituting the number of electrons accepted divided by two for the number of active chlorine atoms. It can also be measured by iodometric titration. 

Vapor phase chromatography was used to analyze allylic oxidation products. The column, inch X 35 feet, was packed with 20% UCON 5100 on Celite (50-70). NMR analyses were performed using a Varian A-60 instrument. Molecular weights were determined by cryoscopic methods (benzene and acetic acid solvents). Organoselenium compounds were analyzed for selenium by the method of Gould (2), which involves wet digestion of the sample, followed by iodometric titration of the selenium dioxide produced. 

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. 

Metal Catalyzed Reactions of a Cyclohexene Solution of Cyclohexenyl Hydroperoxide, V. Solutions of cyclohexenyl hydroperoxide in cyclohexene were prepared by the methods of Gould and Rado (24) and Van Sickle et al. (41). In either case a solution approximately 0.7-0.8M in cyclohexenyl hydroperoxide is obtained (24, 41). Smaller concentrations of VI (—0.01 M), VII (0.09M), and VIII (0.06M) are also present in solution (24, 41). A solution of cyclohexenyl hydroperoxide (8.0 mmoles by iodometric titration) in 10 ml of cyclohexene was rapidly added to 0.20 mmole of the metal complex and heated with stirring under nitrogen at 70°C for 2 hrs. Metal complexes used were [C5H5Fe(CO)2]2, [C5H5Mo(CO)3]2, and [C5H5V(CO)4]. The reaction mixture was then quickly vacuum transferred at 80°C/0.01 mm. Little or no residue remained. Yields in mmoles of the products in solution were obtained by GLPC analysis of the vacuum transferred reaction mixtures. Correction was made for the amount of the product initially present (24, 41). Results are listed in Table VI. 

ALTERNATE PROTOCOL DETERMINATION OF PEROXIDE VALUE BY MEASUREMENT OF IRON OXIDATION The ferrous oxidation/xylenol orange (FOX) method is based on the ability of lipid peroxides to oxidize ferrous ions at low pH. The resulting oxidation is quantitated by using a dye that complexes with the generated ferric ions to produce a color that can be measured spectrophotometrically. Peroxide values (PVs) as low as 0.1 meq active oxygen/kg sample can be determined with this method, providing a distinct advantage over iodometric titration. 

The methods most commonly used for the quantitative assay of / -lactamase are based on one of the following principles (1) Manometric or alkalimetric titration of the new carboxyl group formed by hydrolysis of the /3-lactam ring (2) iodometric titration of the product, and (3)... 

DO in water may be determined by the following two methods iodometric titration (Winkler method) and electrode method. 

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