How to measure the oxygen concentration in 3ml water?

Question

How to measure the oxygen concentration in 3ml water?

Answer 1

Tricky. Where does this small water sample come from?

Gas chromatography might work, although I have no idea how to prepare the column for lots of water and hardly any analyte. Infrared detection might work, or an MS coupling.

Most oxygen membrane electrodes (or measurement cells) require larger amounts of water, so I would propose a wet chemistry approach using a modified version of the Winkler method.

Basically, the problem is to scale the method down to the 3 ml scale. Instead of titration, you could add the reagents using (corrosion-proof) mycroliter syringes. Finding a test tube you can close without enclosing air that holds exactly 3 ml will be tricky, so maybe the experiment will have to be made in a glove box using an inert atmosphere. (This will cause oxygen to diffuse out of the solution, rather than into it...)

Alternatively, make the precipitate in the 3 ml scale, then move to an oxygen-free environment (like the glove box), use oxygen-free water to dilute and perform the titration with low concentration solutions there.

Another approach might be to modify a flow-through spectrometer cell so that it holds just your water sample (inserted manually), and compare it to defined concentrations in the same cell.

Coulometry might work - again, you would have to devise a testing cell working on the 3 ml scale.