Iodine, analytical determination

The moderate reducing character of S203 provides a basis for analytical determination of iodine ... 

Physical Characteristics. The proper blend of basestocks and hardstocks must be identified that provide the physical, functional, and organolepic properties required by the finished product. These characteristics are usually identified analytically with solids fat index, melting point, and iodine value determinations. 

R. W. Liggett (private communication) and Levine have shown that potentiometric iodine titration can be applied directly to the analytical determination of a-dextrin. 

A solution of 9.14 g. of iodine in 1000 g. benzene has a freezing point 0.129° below that of pure benzene (5.400° C) the solid which separates is a solid solution of iodine in benzene. The heat of fusion of benzene is 30.2 cal. g. . Calculate the ratio in which the iodine distributes itself between liquid and solid phases in the vicinity olf 5 C. Compare the result with that obtained by analytical determination as follows the solid phase contains 0.317 g. and the liquid 0.945 g. iodine per 100 g. benzene [Beckmann and Stock, Z, phys. Chem., 17, 120 (1895)]. 

In an analytical determination of arsenic, a solution containing arsenious acid, H3ASO3, potassium iodide, and a small amount of starch is electrolyzed. The electrolysis produces free iodine from iodide ion, and the iodine immediately oxidizes the arsenious acid to hydrogen arsenate ion, HAs04. ... 

Radioactive tracer studies are well suited for zone electrophoresis because the components can be located, analytically determined, and investigated for radioactivity using the same strip (see Fig. 7). The rate of formation of the serum proteins has been studied by incorporation in vivo of valine C (Gros et al., 1952) and of methionine S (Niklas and Maurer, 1952). In vivo incorporation of P into serum has also been investigated with this technique the iodine was found to assemble in a nondialyzable fraction between albumin and ai-globulin in rabbit (Maurer and Teichenbach, 1952) and near a2-globulin in man (Larson et al., 1952). 

Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

Iodine monochloride [7790-99-0] ICl, mol wt 162.38, 78.16% I, is a black crystalline soHd or a reddish brown Hquid. SoHd ICl exists ia two crystalline modifications the a-form, as stable mby-red needles, d = 3.86 g/mL and mp 27.3°C and as metastable brownish red platelets, d = 3.66 g/mL, mp 13.9°C and bp 100°C (dec). Iodine monochloride is used as a halogenation catalyst and as an analytical reagent (Wij s solution) to determine iodine values of fats and oils (see Fats and fatty oils). ICl is prepared by direct reaction of iodine and Hquid chlorine. Aqueous solutions ate obtained by treating a suspension of iodine ia moderately strong hydrochloric acid with chlorine gas or iodic acid (118,119). 

Ana.lytica.1 Methods. Various analytical methods involve titration with oxidants, eg, hexacyanoferrate (ferricyanide), which oxidize dithionites to sulfite. lodimetric titration to sulfate in the presence of formaldehyde enables dithionite to be distinguished from sulfite because aldehyde adducts of sulfite are not oxidized by iodine. Reductive bleaching of dyes can be used to determine dithionite, the extent of reduction being deterrnined photometrically. Methods for determining mixtures of dithionite, sulfite, and thiosulfates have been reviewed (365). Analysis of dithionite particularly for thiosulfate, a frequent and undesirable impurity, can be done easily by Hquid chromatography (366). 

Analytical and Test Methods. Analysis and test methods are similar to those for sodium thiosulfate. Sulfite is determined by an indirect method based on the titration of the acid Hberated when both the sulfite and thiosulfate are oxidized with iodine solution (69). 

Bromine is used as an analytical reagent to determine the amount of unsaturation in organic compounds because carbon—carbon double bonds add bromine quantitatively, and for phenols which add bromine in the ortho and para positions. Standard bromine is added in excess and the amount unreacted is deterrnined by an indirect iodine titration. Bromine is also used to oxidize several elements, such as T1(I) to T1(III). Excess bromine is removed by adding phenol. Bromine plus an acid, such as nitric and/or hydrochloric, provides an oxidizing acid mixture usefiil in dissolving metal or mineral samples prior to analysis for sulfur. 

Sample decomposition is the critical operation in determination of total iodine in complex organic matrix. Iodine in simple form (I ) is highly volatile, so it should be transformed into nonvolatile analytical fomi (iodide or iodate) to prevent loses during the decomposition. 

The luminol reaction has also been used for the CL determination of organic substances such as penicillins [32] and tartrate ion [30] in pharmaceutical preparations by their inhibitory effect on the luminol-iodine and luminol-periodate-manganese(II)-TEA system, respectively. As can be seen from Table 1, the results were quite satisfactory. In the indirect determination of penicillins by their inhibitory effect on the luminol-iodine system, the stopped-flow technique improves the accuracy and precision of the analytical information obtained, and also the sample throughput [32], Thus, in only 2-3 s one can obtain the whole CL signal-versus-time profile and calculate the three measured parameters formation and... 

Automatic Pipettes (Transfer Pipettes) Automatic pipettes are always preferred to ordinary transfer pipettes because of their ability to handle corrosive and toxic liquids in routine analytical laboratories, e.g., determination of Iodine Value in edible oils by iodine-monochloride (IC1) solution. 

Previously (Cataldo and Braun, 2007), it has been noted the interesting correlation between C60 fullerene solubility and the unsaturation level of the fatty acids present in the vegetable oils and measured by the iodine number , an analytical test, which determines the number of double bonds present in the oil by the addition of iodine (Martinenghi, 1963). This correlation is confirmed for C also with the new measurements and is extendable also to C, . The correla-tion is shown in Fig. 13.1 and suggests that the solubility S expressed in milligrams per litre (mg/1) is linked to the iodine number of the oil (NI) according to the following equations ... 

Iodine monochloride is used as an analytical reagent to determine iodine values of ods and fats. It is dissolved in glacial acetic acid (Wijs solution) for the analysis. ICl is used in organic synthesis. It also is used as a topical antiseptic. 

Although simple in conception and straightforward, the standard methods for POV determination require strict observance of analytical quality to avoid interference of artifacts. For example, according to the AOCS methods , the sample dissolved in AcOH-CHCI3 (method Cd 8-53) or AcOH-isooctane (method Cd 8b-90) solvent is treated with aqueous KI and the liberated iodine is titrated with standard thiosulfate solution, using starch indicator. Similar standard methods and modifications have been reported in various countries . 

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 . 

Analytical. Hydrazine content in aqueous solutions is determined by reacting with picryl chloride to form the yellow hexanitro hydrazobenzene, which, with alkali forms red or violet salts that can be measured colorimetrically (Ref 3). More concentrated solution of hydrazine can be titrated with either standard iodine or iodate solutions according to the following equations (Ref 4) ... 

Why discuss distribution coefficients Most everyone is familiar with the demonstration of iodine distributed between an organic and an aqueous layer. However, distribution equilibria are at the heart of many separation processes from liquid-liquid extractions to virtually every type of chromatography in which the distribution of the solute between the mobile phase and the stationary phase determines the effectiveness of the separation. In the practice of analytical chromatography, distribution coefficients are often called partition coefficients but the concept is identical, only the names have changed. The temperature dependence of a distribution coefficient is at the heart of temperature programming in gas-liquid chromatography (GC), and analyses of the temperature behavior depend on the heats of solution of the distributed solutes. Indeed, GC measurements have been used to measure heats of solution. 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The determination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, followed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

The Karl Fisher titration is one of the most common and most sensitive methods used in the analytical laboratory. The titrimetric determination of water is based on the quantitative reaction of water with an anhydrous solution of sulfur dioxide and iodine in the presence of a buffer that reacts with hydrogen ions. This titration is a two-stage process ... 

Excess pyridine was distilled from the flask, and the resulting product was dried under high vacuum at room temperature to a constant weight. The amount of pyridine utilized in the reaction could then be determined by weight difference before and after reaction. Complete analytical results for the crude products obtained with the chlorides and oromides are given in Table II. Because the tantalum(V) and niobium(V) iodides both yielded free iodine in the reaction with pyridine, their products were washed with chloroform, as described later, before analysis. 

Isotope dilution techniques T racer experiments Quantification of analytical data Process control - any material e.g., iodine determination u using... 

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