Iodometric test

This technique is easy to use and its most important merit is that it can readily indicate absence of iodate in case adulterants that give false positive iodometric test are used in its place. The method also enables trace quantities of iodide to be detected even in the presence of large excess of chloride ion. Interferences from impurities normally present in salt were insignificant. 

Select a sample volume of 100 mL for colorimetric test or 400 mL for iodometric test. Add a few drops of zinc acetate solution (10% strength) into the flask and fill it with the sample. Add a few drops of 6 A NaOH solution to produce a pH above 9. Mix the solution vigorously using a shaker. If sulfide is present in the sample, it will form a precipitate. Allow the solution to stand for 15 to 20 min to let the precipitate settle. Decant and discard the supernatant liquid. Add a measured volume of distilled water. Note the final volume of solution containing the precipitate. Begin analysis immediately. 

To a sample of 2 g of resin in 5 mL of cyclohexane is added, under an inert atmosphere, a solution of 0.1 g of Os04 in 10 mL of cyclohexane. After stirring overnight at 25 °C the polymer is filtered off, washed with cyclohexane (20 mL in portions), and dried under vacuum. Iodometric tests on solvent and washing are negative. 

An aq. soln. of TiClg added during 1 hr. at -15° in a Ng-stream to a soln. of the startg. N-chloramine and TiCl4 in 1 1 water-acetic acid until a iodometric test is negative -> product. Y 77%. J.-M. Surzur, L. Stella, and R. Nouguier, Tetrah. Let. 1971, 903. 

Peroxides, test for, 41, 92 Peroxy acids from carboxylic acids and 70% hydrogen peroxide, 43, 96 Peroxybenzoic acid, 43,93 iodometric analysis of, 43, 94 Peroxystearic acid, 43,96 Phenacylamine hydrochloride, 41, 82... 

The most widely used is the iodometric colorimetric method [1,15]. The test is based on measurement of the triodide anion, I3, formed by reaction with a polymer. The concentration of I3 formed may be determined by either titrimetry or UV absorption spectrophotometry (usually about 350 nm). If P signifies the polymer chain, the reaction may be represented as ... 

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. 

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. 

Figure 11. The influence of residual H2O2 on the reaction testing of phenol hydroxylation to catechol (CAT), hydroquinone (HQ), and para-benzoquinone (BQ) [61], Reaction conditions 4 g phenol 50 mL water solvent 0.2 g a-Fe203 catalyst inner standard ethanol reaction temperature 70°C. Aliquots were sampled at different times and analyzed by (a) HPLC and (b) GC to determine the conversions of PHE (A) and yields of CAT + HQ + BQ ( ), CAT ( ), and BQ (T). Aliquots were also analyzed by (c) iodometric titration to determine the conversion of H2O2 (o). [Reproduced by permission of Elsevier from Ma, N. Ma, Z. Yue, Y. H. Gao, Z. J. Mol. Catal. A 2002, 184, 361-370.]...

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). 

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

Peroxide Determinations. Bawn and Williamson report two iodometric procedures for determining peracetic acid (Methods I and III below) and one method for determining total peroxide (4) (Method II). Bawn and Jolly report another method for total peroxide (5) (Method IV below). The difference between total peroxide and peracetic acid is assumed to be acetaldehyde monoperacetate (AMP). Each method was tested in our preliminary studies. Method III is preferred for peracetic acid because the results are more reproducible. In Method I a large blank titration was always observed, while in Method III the blank titration was very small. Method IV is preferred for total peroxide because it seems to be more sensitive to total peroxide and less sensitive to water content of the acetic acid solvent. 

Estimation Gravimetrically as Sulphide as Magnesium Pyroarsenate—Volu-metrically by Iodometric Methods with Potassium Bromate, etc.—The Marsh Test—The Gutzeit Test—Fleitmann s Test—Colorimetric Methods— Microohemioal Methods—Determination of Arsenic in Gases. 

The peroxide value (PV) of an oil or fat is defined as the quantity of peroxide oxygen present in the sample. This classical iodometric method is a volumetric analysis based on the titration of iodine released from potassium iodide by peroxides in a biphasic system using a standardized thiosulfate solution as the titrant and a starch solution as the indicator (see Background Information, discussion of peroxide value). This method will detect all substances that oxidize potassium iodide under the acidic conditions of the test, therefore the purity of the reagents is critical. 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

Presence of oxidizable substances in the sample would interfere in the test, thus giving high results. These include S2. S 0,2. and certain metal ions such as Fe2+ in lower oxidation state. Sulfide should be removed by adding 0.5 g zinc acetate, allowing the zinc sulfide precipitate to settle and drawing out the supernatant liquid for analysis. If thiosulfate is present, determine its concentration in an aliquot of sample by iodometric titration using iodine standard. Subract the concentration of thiosulfate from the iodometric sulfite results to calculate the true value of SO,2. ... 

Although consumption of the hydroperoxide is normally complete, the absence of this peroxide in the reaction mixture should be established by testing with moist starch-iodide paper or by iodometric titration.2 The amine oxide content may be determined by titration with standard aqueous hydrochloric acid after any amine present has been consumed by reaction with methyl iodide for 1 hour at room temperature.3 From this volumetric analysis the submitters determined the yield of amine oxide to be 86%. The checkers found that the reaction could be followed by measuring the n.m.r. spectra in -butyl alcohol solution where the n.m.r. N-methyl signals of the amine (at S 2.03) and the amine oxide (at S 2.98) are readily observed. 

The ozcme test was performed by the courtesy of Mr. M. Roxbury of this Institute. The samples were stretched to 100% extension and hung on a clamp inside the ozone chandler. The ozcme concentraticm was measured by iodometric tritra-tion, foilowir the procedury by C. W. Wadelin (i). The flow rate of ozone through the ozone chamber was adjusted to 25 liter per hour, the measured concentration of ozone was 1,400 ppm. 

Standard Method 4500-0 describes two methods for determination of dissolved oxygen (DO) in water Winkler s iodometric method and the elecrometric method (Standard Methods, 1998). The iodometric method is very accurate and precise, but the electrometric method is far more convenient for field use (e.g. in wastewater treatment system monitoring and control) and produces an electronic output that can easily be converted to digital form for microprocessor monitoring or control of wastewater treatment systems. Also, electrometric methods are not subject to certain interferences (i.e. oxidation or reduction of the iodine indicator). In addition, the iodometric method end point may be obscured by the presence of turbidity or color in textile wastewater samples. The electrochemical method is almost exclusively used in testing of textile wastewater. 

One tried-and-tested technique is the volumetric method (iodometric titration) described in Section 3.2.6.1, involving the use of a known quantity of iodine and back titration of the iodine not consumed. 

The above substitutes for the iodometric determination with one or two exceptions have not been tested for specificity for free SO2. Mathers (1949) on the basis of the fact that free sulfur dioxide is removed early in the distillation of wine proposed that 10 ml. of the distillate from the alcohol determination be mixed with 0.5 ml. of 5% neutral lead acetate and the turbidity of the suspension formed be used to correct volatile acidity for sulfur dioxide. La Rosa (1950) assumed that the color formed on mixing the fuchsin-sulfuric acid-formaldehyde reagent with white wine was a measure of free SO2 but did not give any data to confirm this. The fuchsin procedure and the lead sulfite procedures are very sensitive, the former more so, and can be applied only to very small aliquots or to dilute solutions. 

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