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[B.B.]

Good Morning,

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?

Thanks!
Bev

[phage434]

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.