Can I measure monochloramine on a palintest photometer?
Normally, DPD 1 gives free chlorine
Addition of DPD 3 (excess KI) gives free and combined chlorine (chloramine)
Instead of DPD 3, DPD 2 is used (which has a trace of KI). This only reacts with monochloramine. So subtracting the DPD 1 result gives the level of monochloramine. DPD 2 part code is 1177203 priced the same as the other DPD tablets DPD 1 and DPD 3.
The test can be difficult to get reliable results on due to “noise” in the results (turbidity, bubbles, dirty tubes etc). This “noise” often overwhelms the arithmetically subtraction. Also the chance of accidental KI contamination with the first DPD 1 test is high (you only need a trace in 10 ml). With real care the test can be done though.
This test can be done on a range of photometers such as the Palintest 7500 and palintest 7100.
The full range of Palintest products can be purchased from Camlab in the UK and around Europe