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

Abstract

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 200μgL−1, with coefficient of variation of 1.5% (n=10). The detection limit and the sampling rate were 2μgL−1 (99.7% confidence level), and 22h−1, respectively. Per determination, 48ng of Cu(II), 5μg of ascorbic acid and 0.9μg of BCA were consumed. As high as 100mgL−1 thiocyanate, nitrite or sulfite did not affect cyanide determination. Sulfide did not interfere at concentrations lower than 40 and 200μgL−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.