Effect of additives on the flow-analysis determination of weak-acid-dissociable and total cyanide

Abstract

The effect of reductants, complexants, and nitrite eliminators on the flow-analysis determination of weak-acid-dissociable and total cyanide has been studied for: 1.

cyanide recovery from copper, nickel, and iron complexes; 2.

cyanide generation from the reagents in the presence of common interferents; and 3.

cyanide consumption by the reagents in the presence of those interferents.

In the absence of additives the UV-assisted recovery of (total) cyanide from the iron complexes (using a succinate buffer) was insufficient. Arsenite and hypophosphite had no measurable effect on the recovery, ascorbic acid resulted in total recovery but under these conditions nitrite and sulfite seemed to destroy cyanide. Phenanthroline promoted the recovery of cyanide from iron complexes but led to formation of cyanide from thiocyanate. Citrate resulted in good recovery but in the presence of nitrite cyanide was formed; the recovery with EDTA was also good. It proved necessary to destroy nitrite by use of sulfamic acid. If a combination of EDTA, citrate, and sulfamic acid is used rather high concentrations of thiocyanate, nitrite, thiosulfate, and sulfite can be tolerated in the samples. It is strongly advisable to test modifications of the cyanide determination comprehensively, because some surprising results have been obtained.