In Eq free chlorine and total chlorine can be
In Eq. (7), free chlorine and total chlorine can be measured accurately using DPD colorimetric method (MDL = 0.02 mg/L as Cl2), and NH2Cl can be detected accurately by MonochlorF method (MDL = 0.04 mg/L as Cl2, Hach Co., USA) . However, there is no accredited method for NHCl2 quantification except the MIMS method. In finished water from DWTPs, NHCl2 concentration obtained by [Total chlorine] − [Free chlorine] − [NH2Cl] is actually the sum of [NHCl2] and organic chloramine concentration ([Organic chloramines]), but there is no effective and convenient method to differentiate these tsa inhibitor two parts yet, except the technically demanding MIMS method. Therefore, Eq. (7) should be further transformed as follows:equation(8)[NaAsO2]Total=2.0×([Free chlorine]+[NH2Cl])+20.0×([NHCl2]+[Organic chloramines])[NaAsO2]Total=2.0×([Free chlorine]+[NH2Cl])+20.0×([NHCl2]+[Organic chloramines])
Based on Eq. (8) and the results shown in Fig. 2, free chlorine, NH2Cl and NHCl2 in the practical finished waters can be considered absolutely quenched after the calculated [NaAsO2]Total is added. During the quenching reaction, some organic chloramines, which have some oxidizing capacity, can be also quenched by the excess NaAsO2. For example, chlorinated glycine was prepared (molar ratio of Cl/N = 0.4, pH = 8.0)  and  for NaAsO2 quenching at pH 7.0 in our study and it was found that the chlorinated glycine could be quenched absolutely with only 2 times NaAsO2 molar concentration (data not shown). The result is also consistent with the study of Amiri et al. that chlorinated glycine got some bactericidal ability at pH 6.9 . The remaining part of organic chloramines without oxidizing abilities is the right target we should pay attention to, which we name “ineffective chlorine” in this study.