Sulfide is usually the main interfering species for cyanide determination in waters, because H2S can be generated under similar reaction conditions and diffuse to the PTFE membrane.
In the proposed procedure, it was not observed interferences until40 g L−1 S2−. For higher sulfide amounts (concentrations up to 200 g L−1 were evaluated), addition of 1.6 mmol L−1H2O2sufficedto avoid the interference by oxidation to sulfate.
Other anions which can yield volatile species in acid medium (sulfite, thiocyanate and nitrite) did not affect the analytical signal up to 100 mg L−1.
This was the maximum evaluated concentration and it is considerably higher than the expected to be found in natural waters.