Testing for chloramine count

[BC]

Have a Taylor K-2006 kit. After arriving at a FC count - Add 5 drops R-0003 to titrate using 0871 for CC. Question - is it normal to get the solution colorless at a point but then if left alone for 5-10 seconds the solution begins to turn pink or lighter shade of pink? Once it first turns colorless - calculate the CC at that point? I am mixing thoroughly as well.

Another question regarding UV and it's effect on FC. I understand exposing pool or spa to sunlight reduces FC - will it also reduce CC?
Thanks,
Barry

 

[CaOCl2]

Have a Taylor K-2006 kit. After arriving at a FC count - Add 5 drops R-0003 to titrate using 0871 for CC. Question - is it normal to get the solution colorless at a point but then if left alone for 5-10 seconds the solution begins to turn pink or lighter shade of pink? Once it first turns colorless - calculate the CC at that point? I am mixing thoroughly as well.

In their DPD-FAS test, Palin recommends that the user waits 2 minutes (preferably 4) after getting the clear endpoint to see if the pink returns. If it does, titrate again until clear, and wait again. Repeat until no pink returns.

The Standard Methods specify waiting 2 minutes for dichloramines to break through (4 minutes if the dichloramine concentration is greater than 1 ppm).

Taylor recommends just getting the clear endpoint and no waiting.

Perhaps it makes more sense to wait this 2 to 4 minutes - as dichloramines react more slowly than monochloramines and thus you may get a more accurate reading of CC.

Richard may want to chime in and correct me if I'm wrong.

 

[JasonLion]

The standard Taylor chemistry directions for the FAS-DPD test are to swirl to mix for several seconds and to read the color at that point. It is very common for the sample to turn pink again if left sitting for a while, though that typically takes a minute or more.

Yes, sunlight will break down both FC and CC, though CC typically breaks down much more slowly than FC does. Indoor pools can have problems with CC accumulating, compared to outdoor pools, because they are not getting sunlight.

 

[chem geek]

This link talks about the various chlorine tests, though it's a bit dated (even though written in 2002) and some of the newer tests are more resistant to interference and high chlorine levels. Monochloramine can break through the Free Chlorine (FC) test, but if the FC test is done in under one minute, then this breakthrough is minimal. Nevertheless, if you wait too long when doing the FC test, then you may start to measure monochloramine as FC. As for dichloramines, in practice these will always be at a very low level compared to monochloramine unless there is no FC present. This is because FC will continually oxidize the chloramines and during this process monochloramine is predominant. Any dichloramine is much more short-lived. It's not that it isn't there, but it's in amounts far smaller than measurable in the FAS-DPD test with it's resolution of approximately 0.2 ppm (200 ppb). Nevertheless, you'll read in the link that for the CC test "3-6 minutes of development time is sufficient to resolve all chloramine forms without significant error from competing reactions."

As for the UV in sunlight, it will reduce FC very quickly (half gone every 35 minutes or so), but it will take far longer to reduce CC. Monochloramine will persist for quite a while in sunlight. This is a pain for aquarium users since having a bucket with regular chlorine (hypochlorous acid) just open for a day or put out into the sun for an hour or so was sufficient to mostly remove the chlorine. This isn't true with monochloramine now used in many water supplies. High intensity UV systems used in pools, however, will break down the chloramines and will also somewhat breakdown FC as well though they are tuned to do more of the former and less of the latter.

In practice, if you have a reasonable FC/CYA ratio and not too high a bather load or a urinary discharge incident (i.e. "peeing in the pool"), then you shouldn't be measuring any significant CC, usually < 0.5 ppm. If you do, but it declines over time, then it's mostly monochloramine. If you measure much more and it persists, then this is usually an organic chloramine (chlorine combined nitrogenous organic compounds) and not inorganic chloramine (monochloramine, dichloramine, nitrogen trichloride) though the link says it is questionable that this is measured in the test (but we've had reports of some indoor pools where there was persistent CC that did not behave at all like an inorganic chloramine).

Richard

 

[BC]

Thanks gentlemen. A lot to digest here.
Barry