A multi-pumping flow-based procedure with improved sensitivity for the spectrophotometric determination of acid-dissociable cyanide in natural waters Original Research Article

An analytical procedure with improved sensitivity was developed for cyanide determination in natural waters, exploiting the reaction with the complex of Cu(I) with 2,2′-biquinoline 4,4′-dicarboxylic acid (BCA). The flow system was based on the multi-pumping approach and long pathlength spectrophotometry with a flow cell based on a Teflon AF 2400® liquid core waveguide was exploited to increase sensitivity. A linear response was achieved from 5 to 200 μg L−1, with coefficient of variation of 1.5% (n = 10). The detection limit and the sampling rate were 2 μg L−1 (99.7% confidence level), and 22 h−1, respectively. Per determination, 48 ng of Cu(II), 5 μg of ascorbic acid and 0.9 μg of BCA were consumed. As high as 100 mg L−1 thiocyanate, nitrite or sulfite did not affect cyanide determination. Sulfide did not interfere at concentrations lower than 40 and 200 μg L−1 before or after sample pretreatment with hydrogen peroxide. The results for natural waters samples agreed with those obtained by a fluorimetric flow-based procedure at the 95% confidence level. The proposed procedure is then a reliable, fast and environmentally friendly alternative for cyanide determination in natural waters.