Iodometric Titration Procedure

03 M Na2S2Os Solution. Dissolve 3.7 g of Na2S20s 5H20 plus 0.05 g of Na2COs in 500 mL of freshly boiled water. Add 3 drops of chloroform (a preservative) and store in a tightly capped 

Starch Indicator. Add to 90 mL of boiling water a slurry containing 1 g of soluble starch and 1 mg of Hgl2 (a preservative). The resulting clear solution is stable for weeks. 

Standard Cu. In a fume hood, add 15 mL of water and 3 mL of 70% nitric acid to 0.5 - 0.6 g of accurately weighed reagent Cu wire in a 100 mL volumetric flask and boil gently to dissolve the wire. Add 1.0 g of urea or 0.5 g of sulfamic acid and boil 1 min to destroy HN02 and oxides of nitrogen that would interfere with the iodometric titration. Cool to room temperature and dilute to 100 mL with 1.0 M HC1. 

Standardization of Na Og with Cu. To prevent air oxidation of iodide in the acidic solution, use a 180 mL tail-form beaker (or a 150 mL standard beaker) loosely fitted with a 2-hole stopper. One hole serves as inlet for a brisk flow of N2 or Ar that leaks out the side of the stopper. The other hole is used for the buret. Pipet 10.00 mL of standard Cu solution into the beaker and flush with inert gas. Remove the cork briefly to add 10 mL of water containing 1.0-1.5 g of freshly dissolved KI and begin magnetic stirring. Titrate with Na2S2Os from a 50 mL buret, adding 2 drops of starch just before the last trace of I2 disappears. Premature addition of starch leads to irreversible binding of I2 to the starch, and makes the end point harder to detect. 

Experiment B. Place an accurately weighed 150-200 mg sample of powdered YBa2Cus07 x in the titration beaker and begin inert gas flow. Add 10 mL of 1.0 M HC104 and 0.7 M KI and stir magnetically for 1 min. Add 10 mL of water and complete the titration. 

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Immediately after the discovery of YBa2Cus07 x, numerous groups employed iodometric titration procedures to measure the effective oxidation state of the material, and therefore the value of x. The procedure described below involves two different titrations (10X17X18) and is more accurate than a procedure in which the first titration is omitted (19). Experiment A measures the total copper content of the superconductor and Experiment B measures the total charge of the copper. The two experiments, together, give the average oxidation state of copper. 

As a matter of fact, the CoTRPyP modified electrodes provide a considerable enhancement of the sulfite response and decrease of the overpotential, shifting the oxidation wave to the onset of the Ru(II/III) redox wave ( + 0.70 V vs saturated Ag/ AgClKci)- A similar behavior was observed for the electrostatically assembled CoTRPyP/ZnTPPS films (122, 251). The consistency of the FIA method using modified electrodes was quite good. In addition, the method can be easily scaled up to a large number of samples, in contrast to the tedious and time-consuming iodometric titration procedures. 

The addition of excess calcium acetate to purified cellulosic material suspended in water, followed by titration of the liberated acetic acid, was suggested by L(idtke. From the 0.1% carboxyl content obtained, a D.P. value of 277 was calculated for the cellulosic material employed. This method has been studied further and comparative data with the earlier conductometric titration procedure have been presented by Heymann and Rabinov, by Kenyon and coworkers, and by Sookne and Harris. The latter workers report that electrodialyzed depectin-ized cotton has a carboxyl content of 0.045% or a D.P, of 616. An iodometric titration procedure for estimating carboxyl groups in cellulosic materials has also been described by Ltidtke. The procedure involves a thiosulfate titration of the iodine liberated from a mixture of potassium iodate and potassium iodide by the carboxyl groups of the cellulosic material. The carboxyl content determined by this method agreed well with that obtained by the calcium acetate method. 

The total peroxide content in the cyclohexene feed was measured using the iodometric titration procedure (ASTM D 3703-92). Chemical identification of the peroxides was done through GC/MS analysis as described elsewhere (9). 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). 

When the above procedures fail to give a clean product then dissolve the NaBH CN (lOg) in tetrahydrofuran (80ml) and add N MeOH/HCl until the pH is 9. Pour the solution with stirring into dioxane (250ml). The solution is filtered, and heated to reflux. A further volume of dioxane (150ml) is added slowly with swirling. The solution is cooled slowly to room temp then chilled in ice and the crystalline dioxane complex is collected, dried in a vacuum for 4h at 25°, the 4h at 80° to yield the amorphous dioxane-free powder is 6.7g with purity >98% [JACS 93 2897 797/]. The purity can be checked by iodometric titration [AC 91 4329 1969]. 

Dimethoxycopper(II) is a moisture-sensitive blue compound that is insoluble in common organic solvents. It can be recrystallized from MeOH/NH3 to give a microcrystalline solid. Analysis of copper by iodometric titration provides a quick routine purity determination for dimethoxycopper(II).8 The complete removal of residual chloride from dimethoxycopper(II) is not easily achieved the most likely impurity is CuCl(OMe), which is a green compound.5 Dimethoxycopper(II) must be washed thoroughly as described above to minimize contamination by CuCl(OMe), and is obtained in >98% purity by this procedure (on the basis of the C, H, Cl, Cu, and Li analyses). IR (KBr, cm 1) 2917(vs), 2885(vs), 2806(vs), 1436(w), 1150(w), 1052(vs), 528(vs), 438(s). 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

Using the normal addition procedure (02 diffusion into a 75/25 benzene/THF solution of poly(styryl)lithium) the 37% dimer fraction analyzed for 19% alkyl radical dimer and 18% macroperoxide after LiAlH4 reduction. The yield of macroperoxide was also confirmed by thermal decomposition experiments in refluxing toluene, followed again by size exclusion chromatography analysis of the dimer fraction. The amount of hydroperoxide could be deduced from the difference between the amounts of total peroxide (determined by iodometric titration) versus the amount of macroperoxide determined by LiAlH4 reduction. 

Iodometric titration of the solid product involves the use of 0,2-g. samples of the peracid and the procedure in Note 4. 

The classical method for the determination of low water contents in organic solvents is the nonaqueous iodometric titration introduced by Karl Fischer in 1935, using a solution of sulfur dioxide, iodine, and pyridine in a benzene/methanol mixture [139, 140], By replacing some of the toxic ingredients (pyridine, benzene, methanol), this titration method has more recently been developed into a simple and environmentally safe standard procedure [141]. 

A simple and rapid method for the iodometric determination of microgram amounts of chromium(ni) in organic chelates is based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the umeacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate . Iodometric titration was also used for determination of the effective isoascorbate (see 2) concentration in fermentation processes . The content of calcium ascorbate can be determined with high sensitivity by complexometric titration with edta, which is superior to iodometry. The purity of /3 -diketonate complexes of Al, Ga, In and Ni was determined by complexometric titration with edta at pH 5.5-3, with RSD < 0.01 for determining 5-30% metal ion. Good analytical results were obtained by a similar procedure for the metal content of 15 lanthanide organic complexes. ... 

Another method is the iodometric procedure described by the reviewer (G6, G7), where dissolved mucin was precipitated with 1.5 volumes of acetone at 40°G from trichloroacetic acid filtrate of the gastric juice. Mucin, in the precipitate, was quantitated by iodometric titration with the use of a standardization curve of electrodialyzed mucin solution and methylene blue as indicator. The mucin values of gastric juice determined by this method were 20-210 mg%, those of saliva 50-300 mg %. The method was subsequently used by many investigators, yielding satisfactory results (K6, K20, M25, M52, T33, W20, W21) it was considered to yield accurate results (Przylecki, cited in K20) with 6% error (Labby et al, cited in T33). 

Colourimetric modifications of iodometric titration methods (see Section 6.2.1) have been reported in which the excess iodine is determined at 520nm after reaction with metol and sulphanilamide [86] or in which iodine liberated by reaction of the penicilloic acid with potassium iodate is measured at 520nm [87]. These methods should retain the high specificity of the titration procedures. 

For the preparation of 100, we have used repeatedly and without safety problems the method described in [90], The amount of the dichloroacetylene in the ethereal solutions obtained can be determined either by refractometry [121] or by iodometric titration [90], and typical yields are in the 50% range. As mentioned above, in the meantime several other procedures for preparing 100 [91-93] have been published, which apparently provide a further increase in the ease of access to 100. Furthermore, p. 145 of [10] mentions unpublished work describing the preparation of dichloroacetylene by treating trichloethylene (140) in ether at — 70°C with LDA. Dibromoacetylene (103) has been obtained analogously [10]. 

Inductively coupled plasma atomic emission spectrometry (ICP AES) is a suitable method for determining crystal composition. It has replaced a routine of chemical titration methods (except maybe iodometric titration which is still widely used in the determination of the oxygen content in HTSC). This method is precise enough and it demands only a small amount of substance to be analyzed. Standard solutions as well as an automated measuring procedure are also available. Applications of this method to the analysis of HTSC crystal composition can easily be found in the literature (Yao and Shiohara 1997, Kuroda et al. 1997a,b, Tagami and Shiohara 1997), although some restrictions are evident the ICP technique is destructive and non-local, and it is very sensitive to the selection of the sample to be analyzed since even small flux inclusions in the crystal can affect the results drastically. 

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