Hach Pocket Colorimeter II Instruction Manuals page 48

Chlorine, Free and Total, HR,
Interfering
Substance
Monochloramine
Ozone
Interference Levels and Treatments
For conventional free chlorine disinfection (beyond the
breakpoint), monochloramine concentrations are very low. If
monochloramine is present in the sample, its interference in the
free chlorine test varies with the temperature, the relative
amount of monochloramine to free chlorine, and the time
required to do the analysis. Approximate interference levels of
monochloramine in the free chlorine test are listed below (as
mg/L Cl ).
2
NH Cl Sample Temperature °C (°F)
2
(as Cl ) 5 (40)
2
1.2 0.2
2.5 0.4
3.5 0.5
Interferes at all levels.
continued
10 (50) 20 (68)
0.2 0.3
0.5 0.6
0.6 0.7
1—48
30 (83)
0.3
0.6
0.8