Iodometric determination of active

Iodohexane, 31, 67 Ji-Iodomandelic acid, 35,14 Iodometric determination of active oxygen, 34, 92... 

ISO 2270 1989, Non-ionic surface active agents. Polyethoxylated derivatives Iodometric determination of oxyethylene groups. 

By definition POV is the number of miliequivalents of active oxygen per kilogram of sample" , or in some cases the number of micrograms of active oxygen in one gram of sample, capable of oxidizing iodide to iodine" °°. Many of the methods described in Section V for determination of hydroperoxide classes or individual compounds can also be applied for determination of POV, as total hydroperoxides. The iodometric determination of hydroperoxides in lipids and proteins has been reviewed . 

Russian workers have prepared for pharmacological studies simple carbamates of trachelanthamidine (68) by treatment with the appropriate isocyanate. Some cholinesterase inhibitors based on the standard decamethonium model have been prepared. Decamethylene bistrachelanthamine dibromide (69) showed marked curare-like activity in cats and rabbits. New procedures for the iodometric determination of platyphylline bitartrate and for the colorimetric determination of trichodesmine and incanine in the organs of poisoned animals have been described. 

International Organization for Standardization, Nonionic surface active agents—polyethoxylated derivatives—iodometric determination of oxyethylene groups, ISO 2270 1989. Geneva, Switzerland. 

Apart from the activation of the anode no reagent has to be produced. Nickel peroxide, however, has to be prepared by oxidation of nickel(II)sulfate with sodium hypochlorite. Subsequently the reagent has to be carefully dried and the amount of active oxygen determined by iodometric titration. This must be kept in mind, because small amounts of alcohol need already a relative large amount of nickel peroxide, e.g. 100 mmol alcohol more than 75 g nickel peroxide. For that reason the use of the relative expensive, commercial nickel peroxide is restricted. 

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. 

Oishi et al. (1992) compared the results from classical iodometric PV determinations of edible oils and fats to those using a coulometric detector. Results from each technique expressed as meq active oxygen/kg sample, were consistent with one another. Typical results were sesame oil (4.1), corn oil (8.7), cottonseed oil (14.5), rapeseed oil (33.2), peanut oil (30.5), olive oil (17.0), palm oil (8.9), beef tallow (2.5), and lard (35.0). 

The determination of the active oxygen in ozonides with sodium iodide in glacial acetic acid gives reliable values only in the case of ketozonides. The reaction products are ketones.96 Iodometric peroxide determination in the case of aldozonides gives less than 60% of the theoretical value 112 carboxylic acids are formed as well as aldehydes. The reduction with iodide ions probably suffers competition from the reaction shown in Eq. (7). 

A solution of dibenzoyl peroxide (10 g) in toluene (20 ml) is cooled, with stirring, to —5° and then treated during 5 min with a pre-cooled (—2°) solution of sodium (2 g) in 96% ethanol (50 ml). Sodium peroxybenzoate separates at once. To this mixture is added ice-water, in which the sodium peroxybenzoate dissolves. The aqueous peroxybenzoate solution is separated from the toluene in a separatory funnel and washed twice with ether which removes residual toluene and ethyl benzoate. This purified aqueous solution is cooled and treated with a mixture of concentrated sulfuric acid (5 g) and ice-water (60 g), and the per-oxybenzoic acid liberated is shaken into chloroform (60 ml in two portions). The chloroform extracts are united and dried over sodium sulfate they may then be used for oxidations. For preparation of crystalline peroxybenzoic acid the chloroform is evaporated in a stream of dry air at ca. 30 mm and 25-30°. The content of active oxygen is determined by iodometric titration. 

This reaction is a key part of iodometric titrations, which are used for quantitative determination of oxidants in aqueous samples, such as oxygen saturation in ecological samples or active chlorine in swimming pool water. 

Procedure for determination of total active chlorine content 5 cm buffer solution, 5 cm of the DPD reagent, about 1 g potassium iodide, and 100 cm of the water sample are introduced into an Erlenmeyer flask and homogenized. The absorbance is measured after a 2 min waiting time, as described earlier. If the total active chlorine concentration exceeds 4 mg/dm, then the sample has to be diluted before analysis. Above 10 mg/dm sample concentration, the application of the iodometric method is recommended. 

All monomers, surfactants, buffers, and chain transfer agents were used as provided. Water was deionized. Purchased organic peroxides were all reagent grade. Organic peroxides were prepared from the reaction products of acyl chlorides and sodium peroxide. Activity was determined by iodometric titration. 

Active oxygen content is determined iodometrically 3 In an iodine flask, an accurately weighed sample (0.1-0.3 g.) is dissolved in 20 ml. of an acetic acid-chloroform solution (3 2 by volume), and 2 ml. of saturated aqueous potassium iodide solution is added. The flask is immediately flushed with nitrogen, stoppered, and allowed to stand at room temperature for 15 minutes. Fifty milliliters of water is then added with good mixing, and the liberated iodine is titrated with 0.1 A sodium thiosulfate, employing starch as indicator. A blank titration, which usually does not exceed 0.2 ml., is also run. One milliliter of 0.1 N sodium thiosulfate is equivalent to 0.00821 g. of tetralin hydroperoxide. 

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. 

Oxygen-sensitive membrane electrodes are commercially available. The electrode in such a system is covered with an oxygen-permeable plastic membrane, thus protecting it from impurities. The current is proportional to the activity of dissolved molecular oxygen, and at low concentration, to the amount of DO. Before the measurement of DO in the sample, calibrate the electrodes using standards of known DO concentrations (determined from iodometric titrations). 

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 other varieties of the photometric methods, the calibrating solutions are prepared from sodium hypochlorite. In this case, a concentrated solution is first prepared and its active chlorine concentration is determined with iodometric titration. 

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