Iodine absorption method

Accessibility of cellulose was determined by an iodine absorption method described by Hessler and Power (15) using the following equation ... 

For accurate determination distillation of the formaldehyde from the lozenge base is desirable. A quantity of powdered lozenge, equivalent to about 0 05 g of paraformaldehyde, is steam-distilled in the presence of dilute sulphuric acid into about 100 ml of water until the total volume collected is about 750 ml. The iodine absorption method given above is then used on the distillate. A considerable loss of formaldehyde is liable to occur during manufacture but loss on storage is slow. 

Table 9 shows the classification system for blacks most commonly used in mbber. The ASTM numbering system is based on the fundamental particle si2e of the black. Particle si2e is deterrnined by several methods, including iodine absorption, nitrogen absorption, and light scattering. 

To determine the amylose content of starch, the iodine reaction has been most commonly used because amylose and amylopectin have different abilities to bind iodine. The methods such as blue value (absorbance at 680 nm for starch-iodine complex using amylose and amylopectin standards), and potentiometric and amperometric titration have been used for more than 50 years. These procedures are based on the capacity of amylose to form helical inclusion complexes with iodine, which display a blue color characterized by a maximum absorption wavelength (kmax) above 620 nm. During the titration of starch with iodine solution, the amount (mg) of iodine bound to 100 mg of starch is determined. The value is defined as iodine-binding capacity or iodine affinity (lA). The amylose content is based on the iodine affinity of starch vs. purified linear fraction from the standard 100 mg pure linear amylose fraction has an iodine affinity of 19.5-21.0mg depending on amylose source. Amylopectin binds 0-1.2mg iodine per 100mg (Banks and Greenwood, 1975). The amylose content determined by potentiometric titration is considered an absolute amylose content if the sample is defatted before analysis. 

Fig. 1. Set-up of the PTB laser system. The Nd YAG laser is frequency stabilized onto a selected iodine absorption line using the phase modulation method. The probe beam is modulated at 2.05 MHz by an electro-optic modulator (EOM), the pumb beam is frequency shifted by an acousto-optical modulator (AOM). The driving AOM rf power is chopped in order to cancel frequency offsets introduced by the Doppler background using a lock-in detection scheme. The transmitted probe beam signal is detected by a photodiode (PD) and mixed with the EOM rf in a double balanced mixer (DBM)...

The higher value for canola oil is caused, in part, by the replacement of erucic acid with octadecenoic acids, mainly oleic acid, accompanied by a slight increase in linoleic and linolenic acids (Table 13). The iodine value can also be calculated from fatty acid composition using the specific factors for each unsaturated fatty acid (61). The calculation method provides more accurate data than the iodine absorption assessment. 

In order to effect complete dissolution of starch at temperatures below 100°, Bauer and Pacsu recommended the use either of dilute alkali or of dilute acid solutions. Accoixling to their so-called alkali process, defatted corn starch is dissolved in 0.5 to 1.0 N alkali at room temperature. Sufficient mineral acid is added to the resulting solution to bring its pH within the limits of 10-4. After saturation with (for example) Pentasol (a mixture of primary amyl alcohols), the system is heated for several minutes at a temperature between 60° and 100° on cooling, an amylose precipitate is obtained which can readily be separated in an ordinary, industrial centrifuge. Addition of excess methanol to the supernatant liquor causes precipitation of the amylopectin. Different kinds of starches can be fractionated by this method. Starch concentrations of up to 5% are claimed to give about a 24% yield of amylose (showing an iodine value of 16.0%) and a 76% yield of amylopectin (with a 0.9% iodine absorption). 

Further tests for damage on regenerated cellulosic fibres, such as iodine absorption, core/sheath differentiation, peeling methods, detection of traces of sulphur or copper as well as some hints for investigations on bast fibres are given in the literature. ... 

The extraction of Bils with benzene from H2SO4 solution containing small concentrations of KI forms the basis of the very sensitive indirect starch-iodine amplification method for determining bismuth [36,37]. From the benzene extract, washed with dilute H2SO4, the Bila is re-extracted with water. Iodide is then oxidized to IO3, which reacts with added KI to release iodine, which is determined by tbe starch-iodine method (see Section 25.2.1). For each atom of bismuth (in Bila), 18 atoms of iodine are released. The molar absorptivity e is about 3.2-10 (a = 1.5) [36]. A 48-fold increase in sensitivity of the method has been attained after re-extraction of Bib, adding Br2, and measurement of absorbance of the b" formed [37]. 

The total lead in gasoline may be determined gravimetrically (ASTM D-52, IP 96), polarographically (ASTM D-1269), by atomic absorption spectrometry (ASTM D-3237, IP 428), by the iodine chloride method (ASTM D-3341, IP 270), by inductively coupled plasma atomic emission spectrometry (ASTM D-5185), and by X-ray fluorescence (ASTM D-5059). When it is desired to estimate tetraethyl lead a method is available (IP 116X whereas for the separate determination of tetramethyl lead and tetraethyl lead recourse can be made to separate methods (ASTM D-1949, IP 188). 

For both polymerization and rubber processing it is important to know the type and amount of unsaturation. In this connection IR spectroscopy is perhaps the most useful technique, although it requires a preliminary evaluation of band absorptivities by means of suitable standards, analyzed by an independent technique. A number of methods are available to analyze these standards NMR spectroscopy, the iodine-monochloride method, gas-chromatographic analysis of pyrolysis products, materials balance determination, etc.12 Provided the termo-nomer content of the standard is not too low, the most useful technique is NMR, based on the ratio between the signal from all saturated protons (generally with chemical shifts of 2S from TMS) and the signal from olefinic protons, observed at lower fields (45-5.5 5). 

Three methods have been described for three halogens, two based on fluorescence and one on absorption. In the first [87], the fluorescence of rubrene in polystyrene is quenched by traces of iodine. This method is nonselective and the optode is also sensitive to oxygen. In another sensor, naphthoflavone in solution in a material of the silicone or PVC type serves as a sensitive layer for free halides [88]. The absorption technique uses a fiber with a liquid CS2 core [89] to detect 10 ng of iodide using a S m long capillary cell with sample circulation. The Hber itself constitutes the active optode (total reflection in the liquid core). A comparison of optodes based on dynamic quenching of absorbed Rhodamine 6G by iodide was reported [90]. Three solid supports for immobilization were used PTFE tape, XAD resin beads and crushed XAD-4 resin. The limits of detection are 0.18-0.30 and 1.1 mM respectively. Some anions (eg. Cl , Br , CN ) interfere at the 1-M level. 

A recent study of iodine atom recombination in solution by Luther et al. [294] used a dye laser (wavelength 590nm, pulse duration 1.5ps) to photodissociate iodine molecules in n-heptane, -octane or methyl cyclohexane at pressures from 0.1 to 300 MPa. Over this pressure range, the viscosity increases four-fold. The rate of free-radical recombination was monitored and the second-order rate coefficient was found to be linearly dependent on inverse viscosity. This provides good reason to believe that the recombination of free iodine atoms is diffusion-limited, especially as the rate coefficient is typically 10 °dm mol s . The recombination of primary and secondary pairs is too rapid to be monitored by such equipment as was used by Luther etal. [294] (see below). Instead, the depletion of molecular iodine absorption just after the laser pulse was used to estimate the yield of (free) photodissociated iodine atoms in solution. They found that the photodissociation quantum yields (survival probability) were about 2.3 times smaller than had been measured by Noyes and co-workers [291, 292] and also by Strong and Willard [295]. This observation raises doubts as to the accuracy of the iodine atom scavenging method used by Noyes et al. or perhaps points to the inherent difficulties of doing steady-state measurements. In addition, Luther et al. 

The iodimetric method of assay is favoured for many official purposes and it can be applied, with very little sample preparation, to injections, tablets and solution-tablets. For ointments and similar preparations it is not directly applicable since high results may be obtained due to iodine absorption by the base. For preparations of this type Boymond has recommended iodimetric determination after mixture with benzene and extraction with water. 

A.O.A.C. 17 edn, 2000c, Official method 920, 159 Iodine absorption number of oils and fats. 

The result is that TGA can only be an indicative technique and other more accurate techniques (e.g. surface absorption of nitrogen - BET method, or iodine adsorption method) should be used to obtain a more definitive identification of the black present in a sample after its recovery by non-oxidative pyrolysis. 

I he methyl iodide is transferred quantitatively (by means of a stream of a carrier gas such as carbon dioxide) to an absorption vessel where it either reacts with alcoholic silver nitrate solution and is finally estimated gravimetrically as Agl, or it is absorbed in an acetic acid solution containing bromine. In the latter case, iodine monobromide is first formed, further oxidation yielding iodic acid, which on subsequent treatment with acid KI solution liberates iodine which is finally estimated with thiosulphate (c/. p. 501). The advantage of this latter method is that six times the original quantity of iodine is finally liberated. 

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 deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

Worenine. This alkaloid, also obtained by Kitasato from Coptis japonica was isolated as the tetrahydro-base, C,oHjg04N, which crystallises from alcohol in colourless prisms, m.p. 212-3°, and is oxidised by iodine in alcohol to worenine iodide, yellow crystals from which worenine chloride, thin orange-yellow prisms, m.p. 295° (dec.), can be obtained. Tetrahydro-worenine behaves as a tertiary base, contains methylenedioxy- but no methoxyl groups, and its absorption spectrum closely resembles that of tetrahydrocoptisine from which it differs in empirical composition by. CHj. Worenine is, therefore, represented by (XXX), the alternative position (a) for the methyl group being untenable, since a-methyltetra-hydrocoptisine obtained by Freund s method is not identical with... 

Puacz et al. (1995) developed a catalytic method, based on the iodine-azide reaction, for the determination of hydrogen sulfide in human whole blood. The method involves the generation of hydrogen sulfide in an evolution-absorption apparatus. In addition, the method allows for the determination of sulfide in blood without interference from other sulfur compounds in blood. A detection limit of 4 g/dm3 and a percent recovery of 98-102% were achieved. Although the accuracy and precision of the catalytic method are comparable to those of the ion-selective electrode method, the catalytic method is simpler, faster, and would be advantageous in serial analysis. 

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). 

Oxidative stress Lipid oxidation Oxygen absorption Manometric, polarographic Diene conjugation HPLC, spectrophotometry (234 nm) Lipid hydroperoxides HPLC, GC-MS, chemiluminescence, spectrophotometry Iodine liberation Titration Thiocyanate Spectrophotometry (500 nm) Hydrocarbons GC Cytotoxic aldehydes LPO-586, HPLC, GC, GC-MS Hexanal and related end products Sensory, physicochemical, Cu(II) induction method, GC TBARS Spectrophotometry (532-535 nm), HPLC Rancimat Conductivity F2-iP GC/MS, HPLC/MS, immunoassays... 

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