Formation of thiocyanate during removal of sulfide as lead sulfide prior to cyanide determination

Abstract

Most standard and other analytical procedures for the determination of cyanide suffer from sulfide interferences. As sulfide and cyanide co-exist in many ‘real world’ samples, this presents a significant problem. The standard procedure for removal of sulfide is its precipitation with a lead salt. However, lower cyanide recoveries are often obtained if this procedure is performed improperly. In this paper, the chemistry of the sulfide interferences in cyanide determination methods is explained and procedures are suggested for alleviating the problem.