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WEF Discussion Forums » Laboratory Management and Technical Issues » BOD pH adjustment

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BOD pH adjustment
17577211
Posted: Thursday, September 27, 2012 9:00 AM
Joined: 8/3/2012
Posts: 2

This may have been addressed before but we just recently bought SM 21st Edition and I was taking a look at the BOD method.

 

It says "Check pH; if it is not between 6.0 and 8.0 [adjust temperature], then adjust pH to 7.0 to 7.2..."

 

So, if I recieve a sample and the pH is 6.2 it's ok. But if the pH is 5.5 and I have to adjust it, then 6.8 is NOT ok. Really?? Can someone please explain this to me?

 

Couldn't they just leave it at "Neutralize sample to pH 6.5 to 7.5"?

 

 
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01487708
Posted: Monday, October 29, 2012 11:22 AM
Joined: 10/12/2009
Posts: 10

The 18th edition says "adjust pH to 6.5 - 7.5" so somewhere between this and the 21st a change was made.

 

I am mystified as you.  I would have assumed that the final pH of 7.0 - 7.2 is to make sure the phosphate buffer is not overwhelmed by the use of a strong acid or base, but if that is so then why allow samples to be has high as 8.0 or as low as 6.0.

 
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