Comparison of various sensitive and selective spectrophotometric assays of environmental cyanide

Abstract

A review is presented to show the advantages involved in the use of some new spectrophotometric cyanide (CN) assays, which are highly sensitive and selective, quick and affordable. Among these, the ninhydrin-based assay, the method based on CN reaction with resorcinol, as well as the Berthelot reaction were found to be highly selective. The old Aldridge 1 method, based on the formation of cyanogen bromide and its subsequent reaction with pyridine and benzidine to form a highly-colored polymethine chromophore is still in use, although recent assays using isonicotinic acid–sodium barbiturate are safe, selective, and sensitive (with a detection limit of 0.005–0.01 mg L−1 CN). Ninhydrin-based procedures are suitable to detect low trace amounts of CN with a molar absorptivity below 2.2 × 105 L M− 1 cm−1 and detection limit of less than 1 ng cm−1 CN. The sensitivity, specificity, and reliability of the investigated methods were compared and the most appropriate protocol for a given analytical problem described.