Iodine determination

Last time development of methods of iodine determination, which include preliminary sorption preconcentration of microcomponents and their subsequent determination in phase of concentrate get great practical significance. Silica gel (SG) with adsorptively modified quaternary ammonium salts (QAS) gets properties of anion-exchange resin. The sorbents modified in this way can be used successfully for determination of different anions. 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

Iodine was determined by an iodometric titration adapted from White and Secor.(3) Instead of the normal Carius combustion, iodide was separated from the samples either by slurrying in 6M NaOH, or by stirring the sample with liquid sodium-potassium (NaK) alloy, followed by dissolving excess NaK in ethanol. Precipitated plutonium hydroxides were filtered. Iodine was determined in the filtrate by bromine oxidation to iodate in an acetate buffer solution, destruction of the excess bromine with formic acid, acidifying with SO, addition of excess KI solution, and titrating the liberated iodine with standard sodium thiosulfate. The precision of the iodine determination is estimated to be about 5% of the measured value, principally due to incomplete extraction of iodine from the sample. 

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

The iodine determined by this method, as well ns that obtained under b, and, of course, also die number of enlae centimeters required in the. titrations, provided I be same quantities of potassium biniodate are used, bear the rutin I 12. 

Methods for iodine determination 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, possibility of contamination, and loss during analysis. More recently neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

Volumetric Method, i gram of the minium is treated with 2 4 grams of potassium iodide and 30 grams of crystallised sodium acetate dissolved in a little water, 5 c.c. of glacial acetic acid being then added and the liquid shaken until the lead dioxide is completely dissolved. The solution is diluted to about 100 c.c. and the separated iodine determined by means of standard sodium thiosulphate solution in presence of starch paste I X 0 94193 = PbOj. 

G. Radlinger, K. G. Heumann, Iodine determination in food samples using inductively coupled plasma isotope dilution mass spectrometry, Anal. Chem., 70 (1998), 2221D2224. 

G. Knapp, B. Maichin, P. Fecher, S. Hasse, P. Schramel, Iodine determination in biological materials options for sample preparation and E>nal determination, Fresenius J. Anal. Chem., 362 (1998), 508D513. 

Iodine Number Determine as directed under Iodine Determination, Appendix VII. 

Kucera, J., Randa, Z., Soukal, L. A comparison of three activation analysis methods for iodine determination in foodstuffs. J. Radioanal. Nucl. Chem. 249, 61-65 (2001)... 

Section 12-4 13. Tin(IV) iodide is prepared by reacting tin with iodine. Write the balanced chemical equation for the reaction. Determine the theoretical yield If a 5.00-g sample of tin reacts in an excess of iodine. Determine the percent yield. If 25.0 g Snl4 was actually recovered. 

Phosgene is an oxidising agent, and iodometric techniques, based upon equation (3.2), have been employed for its determination [425,1148,1255,1357,1604]. The reaction must be carried out under anhydrous conditions (commonly in propanone or methyl ethanoate [1604]), and the iodine determined by conventionai procedures, such as by titration with [S fi 3] Although the usual starch indicator cannot be used in propanone solution, the colour of the generated dliodlne affords a reasonably sharp end-point [1560]. In addition, indications of very smali quantities of phosgene are indicated by the reddish-yellow colour of the liberated diiodine, so that the method can be applied for the trace determination of the gas [1560],... 

After having allowed the solution to stand for 15 minutes, it is acidified and the unconsumed iodine determined. One molecule of aldose consumes 2 equivalents of iodine ... 

Bermejo-Barrera P, Aboal-Somoza M and Ber-mejo-Barrera a (1999) Atomic absorption spectrometry as cm alternative technique for iodine determination (1968—1998). J Anal Atom Spectrom 14 1009-1018. 

Hilp M (1998) Optimization of iodine determination according to Schoniger — analytical chemistry with l,3-dibromo-5,5-dimethylhydantoin (DBM) Part 1, oxygen flask combustion Part 7 [1,2]. Fresenius J Anal Chem 360 184-191. 

The solutions required are iodic acid, 50 grms. in 250 c.c. deci-normal sodium thiosulphate 20 per cent, potassium iodide and starch paste. Into the flask of a Fresenius or Mohr s iodometric apparatus, 0-5-0-6 gramme of antimonious oxide is weighed, 20-25 c.c. of iodic acid are added, and 10 c.c. of potassium iodide solution are placed in the condensing apparatus. The contents of the flask are boiled until colourless, and the collected iodine determined with thiosulphate. From antimony compounds the sulphide is precipitated by sulphuretted hydrogen, then dissolved in HCl, and the oxide obtained by the action of sodium carbonate. The halogen acids, sulphurous acid, and sulphuretted hydrogen must be dissolved in... 

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