Anyone have any experience with Oxygen meters?

[rwooduk]

If anyone has used or uses an oxygen meter and could offer some advice it would be greatly appreciated.

I degassed a solution of potassium iodide for 10 minutes each time and did experiments. However to get a more accurate measurement of the amount of O2 present I've decided to use an oxgen meter.

At the same time I am degassing phenol solution and need to do experiments at the same oxygen content as the potassium iodide used in previous experiments.

Q1. the oxgen meter takes a LONG time to stabilise when taking a measurement of degassed solution. It decreases rapidly then decreases slowly until it reaches a minimum value. Is this normal? And am I correct in taking the minimum value it gives i.e. the oxygen probe won't cause further degassing so the minimum value it gives must be the closest value to the truest value.

Q2. for the potassium iodide solution, I have dissolved 16g KI in one litre of distilled water. Am I correct in setting the Salinity value of the meter to 16g/L?

Q3. if i degas 400ml potassium iodide for 10 minutes i get an oxygen value of around 13%. If I degas 750ml of phenol solution (not a salt) for 10 minutes I get an oxgen value of around 10%. Shouldnt the potassium iodide solution hold LESS oxygen because its a salt?

Q4. the idea was to test the oxygen content of the potassium iodide solution after 10 minutes degassing (because I have done this in previous experiments) and THEN make a calibration curve of degas time vs oxygen content for the phenol solution. Which I can then use to decide how long to degas the phenol for to achieve the same oxygen content as I had with the KI solution. HOWEVER the curve isn't linear it decreases rapidly with degas time and then flattens out when the solution becomes full degassed. So how would I go about doing this?

If anyone can make any suggestions regarding one or more of the above questions it would really help our project move forward!

 

[Nidum]

Can you :

(a) measure some secondary quantity and infer the oxygen levels - maybe pH , density or conductivity ?

(b) collect and analyse the gasses removed ?

(c) reverse the process and start with a fully degassed solution to which you then add metred amounts of oxygen ?

 

[Nidum]

What oxygen meter are you currently using ? There are many different ones and there may be something more suitable available .

 

[rwooduk]

Hi many thanks for the reply,

Can you :

(a) measure some secondary quantity and infer the oxygen levels - maybe pH , density or conductivity ?

(b) collect and analyse the gasses removed ?

(c) reverse the process and start with a fully degassed solution to which you then add metred amounts of oxygen ?

What oxygen meter are you currently using ? There are many different ones and there may be something more suitable available .

(a) I could potentially measure the pH, although I am unsure how this would work as phenol turns the water acidic. i.e. I am unfamiliar with this technique, could you perhaps please explain further?

(b) not possible it is degassed via a degas pump

(c) unfortunately we don't have access to oxygen at present as the chemistry department aren't willing to share oxygen due to safety protocols :-/ however to degas and regas samples I think would introduce new problems and we would still need to measure the oxygen content once regassed to be sure of the percentage. But the ideas is very much appreciated, thanks.

What oxygen meter are you currently using ? There are many different ones and there may be something more suitable available .

I only have access to one and we do not have funds to purchase another type. But to answer your question it is a HANNA HI98186 Dissolved Oxygen Meter...

http://www.hannainstruments.co.uk/advanced-high-range-dissolved-oxygen-and-bod-meter.html

I'm not sure if the above info will be of use to the problem? If you have any insights into problems associated with our O2 meter they would certainly be welcome.

thanks again!

 

[Nidum]

One of the problems with immersed probe gauges of all types is that the layer of liquid that the probe is sampling can have different properties to the bulk of liquid .

Main causes are stagnant films and bubble layers . More of a problem with higher viscosity liquids than with lower viscosity ones .

May be worth devising a test procedure which ensures that the liquid around the probe is freely circulating .

 

[rwooduk]

One of the problems with immersed probe gauges of all types is that the layer of liquid that the probe is sampling can have different properties to the bulk of liquid .

Main causes are stagnant films and bubble layers . More of a problem with higher viscosity liquids than with lower viscosity ones .

May be worth devising a test procedure which ensures that the liquid around the probe is freely circulating .

Thanks and yes I believe circulation is the issue! Thanks! I re-read the manual and there is a small sentence hidden away (typical!) which indicates that for accurate measurements a small circulation flow must be applied, basically stirring using the probe. This is because the probe actually consumes oxygen when left in the solution!

Many thanks again for your replies!