Iodometric method

In the iodometric method of OOH concentration determination, a known weight of polymer sample (1-2 g) should be cut into the smallest possible pieces and refluxed for 30 min in a mixture of 2-propanol (8 ml), glacial acetic acid (2 ml) and sodium iodide (0.5 g). Sometimes it is recommended that the cut pieces of polymer be allowed to swell for 18-24h in a given solvent, e.g. chloroform before adding glacial acetic acid and sodium iodide. Instead of 0.5 g solid sodium iodide 1-2 ml of a freshly prepared de-aerated 5% solution 

The iodometric method determines the total concentration of hydroperoxides, peroxides and peracids. In order to determine peracids in the presence of hydroperoxides and peroxides, an equal volume of 7-tetradecene solution (2 X 10 M) is added to a given volume used for analysis. Peracids (R—CO—OOH) react with olefins forming a corresponding epoxide, according to the reaction  

After 16 h standing in the dark, the remaining peroxides and hydroperoxides can be analysed by the iodometric method and determined from the equation [651]  

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An alternative method for the analysis of permanganate is the use of conventional iodometric methods (177) where excess potassium iodide is added to a solution of permanganate under acidic conditions. The Hberated iodide is then titrated with standard thiosulfate solution using starch as an indicator. 

The iodide method can also be appHed to the analysis of other manganese species, but mixtures of permanganate, manganate, and MnO interfere with one another in the iodometric method. 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

Liquid phosgene is assayed by an iodometric method which iavolves the foUowiag reaction (52). The released iodine is titrated with sodium thiosulfate. 

There are also numerous titrimetric methods for determining macro amounts of selenium including the iodometric, thiosulfate, and permanganate methods. In one of the several iodometric methods, the dissolved selenium is reduced from Se(IV), if an excess of potassium iodide is added ... 

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

The iodometric method has the advantage over the permanganate method (Section 10.95) that it is less affected by stabilisers which are sometimes added to commercial hydrogen peroxide solutions. These preservatives are often boric acid, salicylic acid, and glycerol, and render the results obtained by the permanganate procedure less accurate. 

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. 

React iodine with sodium azide Iodometric method 4 p,g/dm 3... 

The methods most commonly used to detect hydrogen sulfide in environmental samples include GC/FPD, gas chromatography with electrochemical detection (GC/ECD), iodometric methods, the methylene blue colorimetric or spectrophotometric method, the spot method using paper or tiles impregnated with lead acetate or mercuric chloride, ion chromatography with conductivity, and potentiometric titration with a sulfide ion-selective electrode. Details of commonly used analytical methods for several types of environmental samples are presented in Table 6-2. 

The Iodometric method has also been utilized in analyzing hydrogen sulfide in the air (EPA 1978). The method is based on the oxidation of hydrogen sulfide by absorption of the gas sample in an impinger containing a standardized solution of iodine and potassium iodide. This solution will also oxidize sulfur dioxide. The Iodometric method is suitable for occupational settings. The accuracy of the method is approximately 0.50 ppm hydrogen sulfide for a 30-L air sample (EPA 1978). 

Experimental set up as in section a). Alkoxy radicals were produced by photolysis of di-tert.-butyl peroxide (2 Mol/1). The build up of hydroperoxide concentration was measured by a modified version of the iodometric method used by Carlsson and Wiles—. 

Among medical technologists the normal limits, using an iodometric method, are considered to be from 0 to 320 units. In a series of 23 individuals the range was from less than 80 up to 1070. Five of these individuals were judged to be abnormal, and one was considered borderline. Two cases of acute pancreatitis yielded values on admission of 1600 and 3200 units, respectively. 17... 

DeMore, W. B., J. C. Romanovsky, M. Feldstein, W. J. Hamming, and P. K. Mueller. Interagenqr comparison of iodometric methods for ozone determination, pp. 131-140. In Calibration in Air Monitoring. Proceedings of Conference, Boulder, Univetsity of Colorado, Aug. 5-7, 1975. ASTM Special Technical Publication 596. Philadelphia American Society for Testing and Materials, 1976. 

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. 

The iodometric determination of hydroperoxides in lipids and proteins has been reviewed . Although the standard AOCS iodometric method for POV accounts for the peroxides present in the sample, interference is possible from the action of air that causes liberation of additional I2, or other moieties present in solution that may react with I2. Thus, alternative methods have been proposed for the determination of this important parameter, such as the analytical kits in Table 2, other spectrocolorimetric... 

Hydroperoxides may be determined by measuring at 290 nm (e = 44100 M cm ) or 360 nm (e = 28000 cm ) the concentration of 13 formed in the presence of a large excess of ions. The reaction may be too slow for practical purposes, unless a catalyst is present. For example, an assay for lipid hydroperoxides conducted without a catalyst may require several measurements every 6 min until the absorbance reaches a maximum. Exclusion of air from the sample cuvette is important. The method is about 1000-fold more sensitive than thiosulfate titration The iodometric method with UVD at 360 was adopted for detecting the presence of hydroperoxides derived from protein, peptide or amino acid substrates subjected to y-radiation, after destroying the generated H2O2 with catalase. ... 

The oxidation of can proceed with hydroperoxides at a convenient rate without a catalyst, if the solution is heated to 90 °C, measuring at 348 nm. A modification of the iodometric method was proposed for determination of hydroperoxides in liposomes, using anhydrous EtOH as solvent in all the operations. A sample of liposome suspension is evaporated to dryness in a vacuum, after adding EtOH in a 4 96 sample-to-solvent proportion. 

Chloroprene Peroxide. The efficiency of conversion of oxygen to total peroxides and hydroperoxide at various extents of oxidation was determined by iodometric methods. At up to 12% oxidation the proportion of hydroperoxide was constant at 20% of the whole. Ferrous thiocyanate likewise estimated a constant proportion (40%) of the total peroxide. Direct analysis of oxidates was somewhat difficult since the chloroprene tended to continue oxidizing during manipulation. Total peroxide estimates on chloroprene-free solutions of peroxide in toluene showed that at 20% oxidation 84% of the oxygen absorbed was present as peroxide groups. This is a minimum value since a small amount of the peroxide may have decomposed while chloroprene was being removed at —20°C. 

The kinetics of the noncatalytic reaction were studied by the method of Bawn and Williamson (4). They found 3.3-3.7 moles/liter for the equilibrium constant for the formation of the intermediate acetaldehyde monoperacetate (AMP) and a first-order rate constant for the decomposition of this intermediate to acetic acid of 0.015 min."1 at 25°C. We found difficulty in reproducing our results probably caused mainly by the high values of the blanks in the iodometric methods used. However, as an average of four determinations we obtained 0.03 min."1 at 30°C. 

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. 

An iodometric method consists in estimating the iodine liberated from a mixture of potassium iodide and iodate,8 excess of which is added to the hydrosulphite solution, the reaction being according to the equation ... 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

In the iodometric method for the quantitative estimation of small quantities of selenium in pyrites use is made of the reaction... 

Redox titrations proved to be the most reliable way to measure the oxidation state of copper and thereby deduce the oxygen content of YBa2Cu30A.25 An iodometric method includes two experiments. In Experiment A, YBa2Cu30A is dissolved in dilute acid, in which Cu3+ is converted into Cu2+. For simplicity, we write the equations for the formula YBa2Cu307, but you could balance these equations for x =A 7.26... 

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