[BaffledBrewer]

Hi all,

I work at a brewery and i am trying to successfully measure the dissolved oxygen content in beer and water etc.

I have a number of dissolved oxygen meter (DO meters) - all of which are reading significantly differently.

They have all been re-membraned and calibrated to a certain temperature and air pressure.

Does anyone know of another method of measuring dissolved oxygen (perhaps a method of capturing the oxgyen in a complex and titrating.

If I knew the correct results - i could then calibrate the DO meters to this standard.

Any help would be appreciated.

Martyn

[xanthocyanopia]

You could do a redox titration - reacting the dissolved oxygen and eventually producing iodine which is then titrated.

The procedure for this can be found
http://physics.slss.ie/downloads/ch_me_9.4student.doc

Unfortunately this really only is an estimation, and is not all that accurate.

[eugenedakin]

Hi BaffledBrewer,

I measure dissolved oxygen all of the time in the oilfield.  Unfortunately, I am only measuring a few parts per million.  Fisher Scientific sells vacuum vials.  You place the tip of the glass vial in a representative sample (it must be representative).  Allowing a small amount of fluid exposed to the atmosphere will change the dissolved oxygen reading.  Next, break the tip of the vial and allow fluid to enter the vial.  Invert the vial several times to mix.  The vial will change colour.  Compare the colour of the vial with the colour chart.  Read the appropriate oxygen concentration.

I hope this helps.

Sincerely,

Eugene

[xiankai]

isnt the above mentioned method more of a qualitative than a quantitative measure? colour change seems quite vague to me...   

[eugenedakin]

Hi Xiankai,

Yes, you are correct.  When attempting to determine the concentration 'by eye', there are definitely large margins of error.   After thinking about this for a while, the colour change can be measured by a spectrophotometer ... much more precise, and a significantly higher degree of replication.

Thanks for the great comments,

Eugene

[Borek]

At the same time it all depends on the required precision. Universal pH papers measure pH in the range 0-14 giving only visual clue.

[xiankai]

i was looking around and i found the "Winkler Test". apparently its quite old (~118 years) but it seems that it is still used, but u can use it as a reference.

http://en.wikipedia.org/wiki/Winkler_test_for_dissolved_oxygen