Is it ok to add more than drop at a time to the FAS-DPD test

pennywise · Jul 6, 2012

Since I have a high CYA value (currently 70 but trying to get it down) I have to maintain around 10ppm of FC.
This equals 20 drops of the FAS-DPD reagent. I don't have the fancy swirling machine so instead of swirling between each drop, I put 5 in, swirl, 5 more, swirl, than start swirling every 2 drops unil I see it start to see the test sample start to clear up. Is this affecting the accuracy of the test by doing it this way (instead of swirling after every drop)?

danivdp · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

I do the same thing

For TA & Ch too....

I actually have perfected a swirl with my right hand while working the dropper with my left. I'm pretty proud of myself, LOL.

pennywise · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

I've tried that and I end up messing up the test!

Suziqzer · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

I tend to do several drops at a time... just keep a close eye on it getting ready to turn so you don't overshoot your mark.

pennywise · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

Thanks a lot. I do keep an eye on it during the process.

techguy · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

I know I tend to do drops in sets of three until I get close to what I am expecting... then I drop to single drops.

chem geek · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

Just make sure that the drops are well-formed when you add them. If you squeeze too hard and have the drops come out too quickly, then they will be smaller drops and that will affect the result making it artificially too high. Also be careful about static electricity which can make the drops "squirt" out. Y'all know what a good-looking drop looks like when you see one...

spidey07 · Jul 6, 2012

Re: Is it ok to add more than drop at a time to the FAS-DPD

Agree on well formed drops. I know where my fc is around so I add 6 full drops and then go from there for my target of 5. Just make sure you swirl really well for a few seconds after the big dose of titrant.

You're doing a titration. Keeping the solution thoroughly mixed is the key. Takes me maybe 5 seconds to get it all mixed up on this test. It's the easiest one.