Determination of Small Amounts of Iodide in Photographic Developers

Abstract

The method for the determination of iodide in photographic developers which is described involves the precipitation of halides with silver nitrate, followed by the oxidation of the iodide to iodate while it is in the form of silver iodide. The concentration of iodate is then determined polarographically.This method can be used for the determination of concentration of iodide as small as 1 mg. per liter of potassium iodide. Amounts around 5 mg. per liter can be determined with an accuracy of about 4 per cent. STUDY of analytical methods for photographic develop-A ers, which has been under way in these labortitories for some time, has given rise to a new method of analysis for iodide in concentrations as small as 6 X 10-6M in the presence of a thousand times the amount of bromide and large amounts of reducing agents. This method involves the chlorine oxidation of the iodide in the form of silver iodide, followed by the polarographic determination of the iodate formed.Rylich (2) first reported the use of the polarograph for the determination of very small amounts of iodate and bromate.He found that concentrations of iodate as small as 1 x M could be readily determined polarographically. The potential a t which iodate is reduced a t the dropping mercury electrode depends on the supporting electrolyte and on the pH of the solution. Below pH 7, the potential varies s i t h pH, but above pH 7, the potential changes only slightly with increasing pH, remaining a t a value around 1.1 volts against the saturated calomel electrode. The polarographic analysis of iodate is particularly sensitive because of the six-electron change which occurs in its reduction. This results in six times the current and, therefore, six times the sensitivity of a reduction involving a one-electron change. Method of AnalysisThe complete analytical procedure finally developed was as follows:Take a 100-cc. sample of the developer and add to it 10 cc. of 0.5 N potassium bromide and 60 cc. of concentrated sulfuric acid. Pass steam through the solution until the small bubbles which indicate gas evolution disappear. To the hot solution add 100 cc. of water and 25 cc. of 0.5 N silver nitrate and pass steam through the solution or boil it for a few seconds to aid in coagulation of the precipitate. Allow the preci itate to settle and pour off the supernatant liquid, leaving t i e precipitate in the flask. To the recipitate add 50 cc. of 1 to 1 nitric acid and 250 cc. of water, stake, and allow to settle. Pour off the supernatant liquid and repeat this process with two 250-cc. portions of water. To the precipitate, add 50 cc. of fresh chlorine water, heat until the bromine color disappears, filter, and wash the precipitate with two 5-cc. portions of water. Cool the filtrate under the tap. To the filtrate add 1.0 cc. of 5 per cent phenol and 5.0 cc. of 2.0 N potassium hydroxide, and dilute to 100 cc. with water. Bubble nitrogen through the solution and electrolyze on the polarograph.The wave obtained can be measured by any of the standard methods (1). The me...

X-Ray Fluorescence Method for Determining Iodide in Photographic Processing Solutions. Iodide Concentration Technique

“…However, even large changes in the amount of bromide in the developer solution-he., 1 gram per liter-have no significant effect on the iodide result, as shown by the iodide counts in Table II. Precipitates from water solutions containing different ratios of sodium bromide to potassium iodide were analyzed for potassium iodide and the results expressed in Table II in terms of net counts per second.…”

“…The chemical methods available consist of potentiometric titrations with silver nitrate (S) or oxidation techniques which attempt to separate the iodide from the other halides (1). The reliability of a modified version of the latter is very poor.…”