Automated Flow Injection Method for Monitoring Total Cyanide Concentration in Petroleum Refinery Effluents Using Ninhydrin as Color Reagent

Abstract

An automated flow injection system was developed for monitoring cyanide concentration in effluents from petroleum refineries. The method takes advantage of the reaction of cyanide ions with ninhydrin in basic medium in a flow injection system. A linear range of 0.01 to 0.04 µg mL^?1 was obtained with a detection limit of 1.5 ng mL^?1 by using 500 µL sample injection, with an analytical throughput of 30 samples hr^?1, excluding sample pretreatment by distillation if required. Regarding interferences, cyanide can be determined in the presence of 100 mg L^?1 of thyocianate and sulfide, both species normally found in industrial effluents. For total cyanide determination, strong acid distillation is recommended due to the presence of cyano‐metallic complexes in the refinery effluents. The method was validated by analyte addition and results compared with the standard methodology proposed by the American Public Health Association (APHA). The more significant advantage of the proposed method is the lack of use of carcinogenic reagent such as pyridine and psychotropic compound such as barbituric acid, both used in the recommended method by APHA. Thus, the proposed method is really a friendly analytical procedure.