Coulometric Titrations with Mercury(I and II). Determination of Cyanide

Abstract

sition a t lower p H levels, with complete breakdown resulting from refluxing with mineral acid.Aliquots of the various solutions were tested for their content of free isonicotinic acid, the breakdown product, using essentially the method of Rubin and associates (4) based on the bromocyanogen reaction of Mueller and Fox ( 3 ) . With decreasing assay values for iproniazid, concomitantly increasing quantities of isonicotinic acid were found.Other aliquots of the solutions refluxed for 10 hours were subjected to paper chromatography, using butyl alcohol saturated with water as the mobile phase. The spots were developed in a chamber containing crystals of cyanogen bromide and the paper was then sprayed with a 1% alcoholic benzidine solution. Reddish spots, with an R, value of 0.16 identical with those of isonicotinic acid run in a parallel experiment, were obtained. Solution 1 showed large quantities of isonicotinic acid, solution 2 showed a distinct band of much less intensity, while solution 3 indicated only faint traces of isonicotinic acid, In a corresponding experiment, samples of iproniazid sirup, buffered a t various pH levels, were stored for 2 months a t room temperature and a t 45" C. While no loss was found with the colorimetric method in any of the samples stored a t room temperature, the samples stored at 45" C. showed the following losses in potency:Cent Loss Sample pH 1 month 2 months 4 5 6 4 14 1 2 Xone None Application to Related Compounds. d series of analogs was subjected to the colorimetric reaction a t the usual concentration of 0.2 mg. of base per ml. The results are listed in Table IV, in order of their decreasing absorbance. It would appear that compounds of the following general structure will produce such a color:// 0 R'-C-XHSHC-R where R = alkyl or aryl and R' = pyridine.

Amperometric Titrations

“…In the coulometric titration of cyanide, Przybylowicz and Rogers (97) found that the results with electrolytically generated mercury(II) were slightly superior to those with silver(I) generated under the same conditions.…”

Electroanalysis and Coulometric Analysis

“…Primary amines interfere in the latter determination, but these can be removed by reaction with salicylaldehyde; tertiary amines do not interfere. Mercuric ion was reported to be slightly superior to silver ion for the titration of cyanide (118). Microgram amounts of sulfide could be titrated with errors of the order of ±0.2% (119).…”