Specificity of the DPD and amperometric titration methods for free available chlorine. A review

Both the DPD and amperometric titration methods for measuring free available chlorine (FAC) are subject to interference from monochloramine and organic chloramines. The measured FAC concentration in the presence of chloramines is often significantly larger than the true FAC residual. Interference in the DPD method can be reduced by rapid titrations. Interference in the amperometric titration method can be minimized by maintaining a 200-mV positive potential on the platinum electrode.