FAS/DPD questions

[Rangeball]

I recently received my FAS/DPD stuff from Dave at TF test kits. Makes me never want to go back to OTO testing for chlorine

The procedure I've been following is-

1- 10ml sample of pool water.
2- Add DPD powder until the sample turns pink.
3- Add drops of R-0871 until sample turns clear. Divide drops by 2 (each drop is .5 ppm of FC) to get FC.
4- Add 5 drops of DPD #3. If sample turns pink, CC is present.
5- Add drops of R-0871 until sample turns clear. Each drop is .5 ppm of CC.

So far so good

What I'm wondering is do I have to test for FC first, or if all I want to know is if CC is present can I simply take the 10ml sample, add the 5 drops of DPD #3 and then add R-0871 to measure CC?

Thanks

 

[duraleigh]

Great question.....I don't know the answer.

I'll be as interested to find out as you.

 

[Wolfmarsh]

This would be simple enough to test, and only cost you a few drops of reagant.

Do the test the way the instructions say to, and then try it the other way and see if you get the same results.

 

[Rangeball]

Wolfmarsh, that's logical, but with any luck, my CC is now gone

If it's not after I test tonight, I'll try it.

 

[Guest]

What I'm wondering is do I have to test for FC first, or if all I want to know is if CC is present can I simply take the 10ml sample, add the 5 drops of DPD #3 and then add R-0871 to measure CC?

Thanks

No, you would be testing TC then, not CC.

 

[Rangeball]

Darn the bad luck...

Is there any way to ONLY test for CC?

Just curious.

 

[Poseidon]

I asked the very same question not long ago. Got the same answer too

 

[Guest]

Darn the bad luck...

Is there any way to ONLY test for CC?

Just curious.

Yes, first add the dpd powder to the sample and add the titrant until the red color changes to colorless, do not worry about counting the drops, just add them until a drop turns it colorless. This will remove the FC from your sample. Then add 5 drops of the dpd #3 reagent and titrate but count those drops. You have just tested for only CC. (since you didn't count the drops in the first part you don't know what your FC or TC is!)

by definition CC is the difference between the TC and FC. In FAS-DPD testing you are depleting the FC in the sample and then test the CC remaining. In DPD testing you test the FC and then the TC and subtract since you are adding the CC to the FC when you add reagent #3, giving you the TC.

 

[Rangeball]

Ok, so that's a no.



Thanks.