Oxygen Probe - Using sodium hydrosulfite to make a 0% standard (Jun/03/2011 )
I'm measuring the oxygen concentration of samples using a FOXY probe, and have been instructed through the manual to use sodium hydrosulfite (also known as sodium dithionite) to create a 0% standard, so I can create a calibration curve.
My problem is, that I don't know how much to use. From what I have read, this white crystaline powder is a strong reducing agent and removes oxygen from solution. Made fresh is can last up to 24 hours. From the research I've done online, I can't seem to find a standard weight to use.
One paper I came across quoted that they used 1M (so with MW of 174.11, and volume required 20ml, that's 3.48g).
Whereas another paper stated that they used a 2-5% solution (again, in 20ml, that's 0.4-1g - nearly x9 difference!)
Again, another paper uses just 0.2g in 20ml.
My ultimate question: can you use too much sodium hydrosulfite? I guess the most you could do is 'overstaurate' the solution, and you can't have a negative oxygen level.
Has anyone else used this chemical to create an 0% O2 standard before? What values did you use?
It won't matter. The dithionite is wildly in excess for removal of the dissolved oxygen, and you just need to remove the oxygen. I'd use the 2% number. It's nasty stuff -- use a hood.