I feel I may have a problem so i wanted to perform an OCLT tonight. I brought my FC to shock value just because I'd like to for the night. When measuring FC I got 23, then I tested again just to see what I'd get; I got 24. So I decided to split the difference and go with 23.5. Just to see what I'd get if I checked FC a third time I did...21. Well, okay let's test again...22. If I am only allowed 1ppm change in FC over the night and my start FC is anywhere from 21-24ppm in the course of 10 minutes I am confused. Why am I getting such a varied FC with back to back checks and how am I suppose to be accurate within 1ppm in the morning?
FC for OCLT
- Thread starter dsilchenstedt
- Start date
This comes up from time to time. What about doing the 25ml test and multiplying by 0.2?
Here is a thread, DPD Powerder Test with comments from some pros.
Also, more in depth instructions here in post #4, Extended Test Kit Directions
Here is a thread, DPD Powerder Test with comments from some pros.
Also, more in depth instructions here in post #4, Extended Test Kit Directions
Thank you Pooldv, I thinks these links answered my questions. Much appreciated.
I have to redo my OCLT but your links gave me the info I needed to solve my issue. I wasn't holding my bottle vertical and going slow. This morning I did the FC twice and got the exact same results by changing my drop technique. Thanks again.
DaninFLA
0
another thing that can affect your FC readings is the volume of water. when dealing with the 10ml line you have to really make sure you have the exact same water level each time for the OCLT. if you have 10.0 ml sample for the first test, but the second test you have a volume of 9.5ml, that's a difference of 5%. when you have a FC of 24, 5% is 1.2ppm. so you can see that a very small difference in volume can make a big impact at that high of a FC....
for normal testing of FC, say at 7ppm, those two volume differences would only make a difference of 0.3ppm which is outside the range of accuracy.
make sure you are placing the tube on a level surface and getting eye level with the water level. fill it till the bottom of the curved water surface is right on to 10 line. and make sure you do it the next day too. the difference in filling the water to 10ml and 9.5ml is not much, very easy to do. even 9.0ml can look like 10ml if you are looking at it from a downward angle
like I said, for normal day to day testing its not a big deal, but when you are doing the OCLT you need to try and be accurate.
for normal testing of FC, say at 7ppm, those two volume differences would only make a difference of 0.3ppm which is outside the range of accuracy.
make sure you are placing the tube on a level surface and getting eye level with the water level. fill it till the bottom of the curved water surface is right on to 10 line. and make sure you do it the next day too. the difference in filling the water to 10ml and 9.5ml is not much, very easy to do. even 9.0ml can look like 10ml if you are looking at it from a downward angle
like I said, for normal day to day testing its not a big deal, but when you are doing the OCLT you need to try and be accurate.
DaninFLA
0
Chem Geek would probably fallen off his chair happy had you used the word meniscus instead of "curved water surface" huh? LOL
DaninFLA
0
you know I was going to, even had it typed in there, then I said no...lets go layman's term
Quick Tip---- Go to a pharmacy and ask for a 10ML syringe, they are free with medicine. I use it to measure 10ML consistently for my FC test every time I preform my test. It stores perfect inside the K-2006 laying on top of the reactant bottles on an angle.
My problem was how I held the bottle and how fast I dropped. The original links posted were exactly what I needed. The rest of the tips are just icing, thanks guys.
Ps I'll be in the lab Monday and planned on grabbing some used 10ml saline flushes for measuring, great minds think alike
Ps I'll be in the lab Monday and planned on grabbing some used 10ml saline flushes for measuring, great minds think alike
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