Chem Qestion

[jimster]

Is there a chemical on the maket for hot tubs that we can buy to tell if someone has urineated in the tub

[chem geek]

There's not a simple dye to be used if that's what you are asking. Urine composition is similar to sweat (it's just more concentrated) as shown in Table 4.1 on marked page 62 (PDF page 85) in the document at this link. Urea breaks down into carbon dioxide and ammonia. If there is not enough chlorine to oxidize the ammonia and urea, then there will be a leftover excess of ammonia and you should find that FC is near zero, you may measure some CC, and you can measure ammonia directly using inexpensive ammonia test kits typically used for aquariums. Basically, just treat urine as you would normal sweat in that you just add chlorine until you consistently measure a residual FC.

[jimster]

Many thanks for the infomation above

[chem geek]

One qualification I need to make if indeed there is a large amount of sweat or urine. You need to add enough chlorine (FC) not only until there is a residual, but once you measure a residual then measure the CC as well (within a few minutes of adding the chlorine and mixing). Then add an additional chlorine amount so that you raise the FC to at least the CC amount (never mind the traditional 10x rule, I won't get into why that isn't actually correct here). The reason you need more chlorine than to just provide a residual is that the chlorine will initially quickly combine with ammonia/urea from sweat/urine to form CC and then that takes longer to break down using additional chlorine. The CC technically requires half it's amount in chlorine to break down, but using an equivalent amount (both measured in ppm using the chlorine test) is sufficient.

Richard

[jimster]

Hi Chem qeek Im usining Bromine in my tub so would the the same instuctions above apply I also use aquacheck strips any advice on this is much appreciated thanks

[chem geek]

Bromine will also break down ammonia/urea, but you can't test for intermediate compounds separately as readily. Probably the safest thing to do is to add some non-chlorine shock to the water which will oxidize any remaining ammonia/urea and if any is leftover it will create more bromine. If you consistently measure bromine levels that aren't dropping faster than usual, then I'd say you've gotten rid of all the urine. With bromine, you have to look at it's rate of usage rather than its level to know if it's finished oxidizing urine.

[jimster]

Many thanks mate if I suspect anyone has done the dirty I may just change the water as well as a good strong dose of bromine however its a shame that there isn't a dye on the market that would pinpoint the the person responsable