Reagents potassium iodide, acidified

Note Tertiary amines and quaternary ammonium compounds yield stronger colors than primary amines [25]. The dipping solution can also be used as spray solution [44]. Other reagent compositions have also been reported in the literature (1, 3, 6, 12, 13, 15, 18, 21, 23, 41] In some cases the reagents have been made up in acetone [38, 39], methanol [14] or ethanol [37] and/or acidified with hydrochloric acid [3, 33, 37-40]. The concentrations of hexachloroplatinic(IV) acid have been in the range of 0.05 -0.4 those of potassium iodide between 0.5 and 24spray solution containing 2% potassium iodide and 0.23170 hexachloroplatinic(IV) acid hexahydrate in N-hydro-chloric acid is reported to yield the best coloration results with respect to detection sensitivity and color differentiation in the detection of morphine, codeine, quinine, methadone and cocaine [46]. Acidic reagent solutions have been recommended for benzodiazepines [10, 11]. Sulfones do not react [39]. 

Potassium iodate is an excellent primary standard for thiosulfate solutions. In this application, weighed amounts of primaiy-standard grade reagent are dissolved in water containing an excess of potassium iodide. When this mixture is acidified with a strong acid, the reaction... 

The aqueous solution (A) contained the non-extractable quaternary bases. It was acidified with hydrochloric acid, filtered and precipitated with concentrated Mayer s reagent (50 g. of mercuric chloride, 200 g. of potassium iodide, 400 cc. of water), added with constant stirring. The precipitate was filtered, suspended in hot water, and hydrogen sulfide was bubbled through the suspension until all the mercury was precipitated as sulfide. The hot filtered solution on cooling yielded candicine iodide (hordenine methiodide) in straw-colored needles. The salt was recrystallized from hot water with the aid of charcoal and yielded colorless crystals, which melted at 234°. The mother liquors contained only small amounts of candicine. Total yield 16.4 g. of candicine iodide 2% of candicine on the dry plant. 

Procedure. The proportions used in the following procedure and the order of the successive additions should be adhered to both in the standardization of o-iodosobenzoic acid and in the determination of residual reagent after reaction with —SH containing substances. Exactly 10.0 ml. of the o-iodosobenzoic acid is pipetted into a flask containing 5 ml. of the phosphate buffer. The measured amount of solution of the sulfhydryl compound to be analyzed is added at this stage. After 30 seconds (or such longer time interval as may be determined by experiment) the acidified potassium iodide is added. The liberated iodine is immediately titrated to a starch end point with the standard thiosulfate. 

Larson and Jenness (89,90) have adapted the apparatus used for the dead stop titration (40,130) to the amperometric determination of —SH groups with o-iodosobenzoic acid. The —SH groups are oxidized by o-iodosobenzoate at pH 7 a mixture of acidified potassium iodide and sodium thiosulfate is then added. o-Iodosobenzoate is added to the first appearance of free iodine as determined amperometrically. Iodine can be used directly but this reagent might oxidize —SH groups beyond the —SS— stage and might react with tyrosine and tryptophane residues. The procedure of Larson and Jenness may be of particular value in the analysis of turbid suspensions such as milk or in the presence of denatured proteins. With such suspensions evaluation of the end point with starch in conventional titrations with sodium thiosulfate is difficult. 

Potassium nitrite solution iodine is liberated when this reagent is added to an iodide solution acidified with dilute acetic or sulphuric acid (difference from bromide and chloride). The iodine may be identified by colouring starch paste blue, or chloroform violet. 

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