Titration iodine

The sample is pyrolyzed in an 80/20 mixture of oxygen and nitrogen at from 1050 to 1100°C the combustion gases are analyzed by iodine titration or by UV fluorescence. Up to 20% of the sulfur can escape analysis, however. 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Transfer 25 ml. of this dilute solution by means of a pipette to a conical flask, and add similarly 50 ml. of Ml 10 iodine solution. Now-add 10% sodium hydroxide solution until the liquid becomes pale yeilow in colour, and allow the solution to stand, with occasional shaking, at room temperature for at least 10 minutes. Then acidify with dilute hydrochloric acid (free from chlorine) in order to liberate the remaining iodine. Titrate the latter w ith Mho sodium thiosulphate solution, using starch as an indicator in the usual way. 

To assay liquid biomine, an ampule of biomine is cmshed under tfie surface of an aqueous potassium iodide solution and the resultant iodine titrated with standard sodium thiosulfate. 

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. 

The USA Military Specification (Ref 8) contains the following chemical criteria and requirements (1) As2Os by sodium thiosulfate—iodine titration 99.0% min, (2) As203 by carbonate-iodine titration 0.05% max, (3) Cl as AgCl turbidity 0.005% max, (4) heavy metals as PbS turbidity 0.010% max, (5) Fe as a Fe(CNS)3. 9KCNS.4H20 red coloration 0,010% max and (6) nitrate as an indigo carmen blue coloration which persists for over 5 mins... 

The substance is burned on a platinum catalyst in a stream of oxygen and the iodine liberated is oxidised to iodic acid by bromine in acetic acid. After excess bromine has been removed with formic acid, potassium iodide is added to the solution, and the iodine liberated is titrated with thiosulphate. Since the amount of iodine titrated is six times the iodine content of the substance the method yields very accurate results. 

Residual Titration Method (Excess of Iodine Titrated with Sodium Thiosulphate)... 

The NaHSOg was analyzed by iodine titration and was typically 97-98% of the expected SO2 content. Several of the solutions used for vapor/liquid equilibrium experiments were analyzed for total SO2 and found to contain 5 to 10% less than the nominal concentration. Nominal concentrations were used in presenting and analyzing the data, unless noted otherwise. Therefore, correlated values of Pgc may he 5 to 10% low for a given solution composition. 

Series 8 in combination with earlier series was intended to provide data on the effects of total anion concentration. The results are internally consistant with the correlation, having a standard deviation of about 15% around the mean error. However the measured values of PSO2 were about 40% lower than the general correlation. An SO2 analyzer, rather than iodine titration, was used to determine SO2 gas concentration from the saturator. The analyzer was calibrated with dry SO2/N2 span gas. In later experiments it was shown that humid gas gives a lower analyzer response. With constant fraction neutralization increased anionic concentration increases PSO2 because pH decreases faster than effective bisulfite activity. 

Often, to make the endpoint of an iodine titration more obvious, an indicator solution that contains starch is added to the solution being titrated. Starch forms a deep blue complex with triiodide. Is", but it is colourless with l . As long as there is unreacted vitamin C in solution, no triiodide ions will be present in solution. Therefore, the blue colour will appear only at the endpoint. 

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 . 

This method is especially suited to the trithionates and tetrathionates, and is applicable even in the presence of thiosulphate or sulphite by first titrating the neutral solution with iodine, which indicates the total quantity of sulphite and thiosulphate, and then determining the acidity developed during the iodine titration, from which the amount of sulphite can be calculated. Finally the mercuric chloride reaction is applied to another portion of the original solution and by determination... 

If larger quantities of arsenic are present, arsenic may be deposited on the cathode, but at high electric potentials and low temperature, arsine is evolved quantitatively and may be absorbed in a solution of iodine in potassium iodide and the excess of iodine titrated. Suitable forms of apparatus have been described.4... 

Ascorbic acids reduce Fehling solution in the cold, and react with ferric chloride to produce the violet color typical of enolic compounds. They are readily oxidized reversibly to their primary oxidation products, 2,3-glycodiulosono-1,4-lactones (commonly known as dehydroascorbic acids 148, Scheme 16), by such mild oxidizing agents as aqueous iodine. Titration with such oxidants constitutes a quantitative method for distinguishing ascorbic acids from 2-glyculosonic acids. 

The fraction of Ca(0H)2 reacted at any given time can be calculated by integrating the S02 versus time curve obtained by the recorder on the SO2 analyzer and doing a mass balance in the reactor. As a backup, the reacted solids are analyzed for sulfite and hydroxide using acid/base and iodine titrations. 

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