Quantitation of Interferences under Equilibrium Conditions with Application to Free Chlorine Analysis in the Presence of Organic Chloramines

The measurement of free chlorine in chlorinated natural waters is subject to interference by organic chloramines. Quantitation of this interference is problematic, since organic chloramines can hydrolyze to free chlorine. This work describes a general model for the simultaneous determination of degrees of interference and analyte-interferent equilibrium constants, with application to the organic chloramlne-free chlorine system. Amperometric membrane electrode responses ranged from 1 (N-chlorocyanurate) to 52 (N-chloro-5,5-dlmethylhydantoln) times the true equilibrium [HOCI]. The model allowed for the evaluation of the hydrolysis constants of N-chlorosuccinimide (pK = 6.46), M-chloro-cyanurate (pK = 4.80), and A/-chloro-5,5-dlmethylhydantoln (pK = 8.24).