Test if it is possible to explain the know ORP reduction when adding H2O2 into a saltwater

[Randy Holmes-Farley]

OK here is a thought. When I added the food slurry to the "off line" sample it had already been dosed with H2O2 and it interfered with the time to minimum...just a quick thought.

Just a comnent on drop and rise times.

The ORP change when mixing fluids will depend on how readily the chemicals can actually react with one another. Some react almost instantly when they encounter one another (say, Cu+ and Fe+++) and some may react quite slowly in the absence of catalysts (say, O2 and ascorbic acid). Thus, the rate of change may be impacted by kinetic factors of the actual electrochemical reactions involved.

 

[taricha]

OK...I am on it...Should finish sometime tomorrow

What on the electrode is being modified?

Let me attempt to unpack what I'm observing with my probe (see post 213)
There are likely deposits on the probe that can be reduced or oxidized. If I "pre-condition" this probe in a strong oxidizer like bleach (it also happened in persulfate+tank water), then the deposits are unusually oxidized. I can rinse/scrub in tap water and place in the tank water for hours or days and the environment is not strong enough to undo all of the oxidation. Upon addition of H2O2 (which can oxidize some things and reduce others) to the tank water, some of the highly oxidized deposits on the probe are reduced, showing an immediate ORP drop. This drop recovers over hours, and later additions of H2O2 repeat the same drop (data later today).

On the flip-side, if I "pre-condition" the probe in a reducing environment, like my pH/ORP storage solution apparently (I'll try thiosulphate / Prime as well) , then the deposits on the probe become unusually reduced. Rinse/scrub in tap water and holding in tank water for hours or days doesn't fully undo this either. Later addition of H2O2 to the tank water then oxidizes the deposits, showing an immediate ORP jump, followed by a slow decline. This too is persistent and repeatable over days.

This explains why my probe usually behaves unlike others in the hobby - ORP rise with H2O2 (my storage solution reduces some important deposits on the probe), and it explains the one time months ago that I found my probe to show an ORP drop in tank water with H2O2 - because I was using my ORP probe to look at oxidizing substances in tank water samples with bleach at the time.

It may be the case that the deposits on the probe explains a lot of what we are seeing as Lasse says.

Something with age is important in the way our probes react

 

[Lasse]

This afternoon I add on ampule of vitamins into the aquarium - the skinner run out of orders but no reaction from probe A and C

Probe C

Probe A

Sincerely Lasse

 

[taricha]

If I "pre-condition" this probe in a strong oxidizer like bleach (it also happened in persulfate+tank water), then the deposits are unusually oxidized. I can rinse/scrub in tap water and place in the tank water for hours or days and the environment is not strong enough to undo all of the oxidation. Upon addition of H2O2 (which can oxidize some things and reduce others) to the tank water, some of the highly oxidized deposits on the probe are reduced, showing an immediate ORP drop. This drop recovers over hours, and later additions of H2O2 repeat the same drop (data later today).

Here's the data follow up, after "pre-conditioning" my probe in dilute bleach, 3 repeated peroxide additions to the tank water, almos 24 hours later the effect still remains.
This one (posted earlier) was done at ~an hour after putting the probe in the tank.

after 16 hours in the tank, repeated with same result (half the peroxide - didn't feel like slamming the tank with too much h2o2)

Then one more time at 22 hours in the tank...

So neither scrubbing, tap water rinse, a day in the tank, or 3 doses of peroxide undid the "pre-conditioning" of 1/100 diluted bleach.

I then soaked the probe in 1/10 diluted Prime (thiosulfate-like) for 20 min. Then rinse, scrub, back in the tank for an hour and the next h2o2 dose made the ORP jump (+20mV) up instead of down. No pic of that data.

 

[Dan_P]

Here's the data follow up, after "pre-conditioning" my probe in dilute bleach, 3 repeated peroxide additions to the tank water, almos 24 hours later the effect still remains.
This one (posted earlier) was done at ~an hour after putting the probe in the tank.

after 16 hours in the tank, repeated with same result (half the peroxide - didn't feel like slamming the tank with too much h2o2)

Then one more time at 22 hours in the tank...

So neither scrubbing, tap water rinse, a day in the tank, or 3 doses of peroxide undid the "pre-conditioning" of 1/100 diluted bleach.

I then soaked the probe in 1/10 diluted Prime (thiosulfate-like) for 20 min. Then rinse, scrub, back in the tank for an hour and the next h2o2 dose made the ORP jump (+20mV) up instead of down. No pic of that data.

Excellent. You can turn the effect “on” and “off”and reproducibly. If someone can confirm your findings, I’d say it is time publish!

 

[Lasse]

More interesting findings

Probe C - H2O2 addition 00:05

A dip followed by a rise !

Control (Probe A) did a normal dip. Note - it looks like the dip is before the addition but the sample time is 10 minutes and in this case last sampled value was just some minutes before the addition.

Probe B also indicate a dip - but still erratic.

Probe D still out of the chart

How connect these results with @taricha ´s result with "pre-conditioning"? Note -that I have stopped my oxidator since I started this test in the DT. The same reason why Taricha took lesser H2O2. Is it a question of electrolyte balance instead for biological reasons?

Another observation Probe C has been around 100 mV below Probe A - but is now much closer to probe A - 20 mV

Sincerely Lasse

 

[Rick Mathew]

Here's the data follow up, after "pre-conditioning" my probe in dilute bleach, 3 repeated peroxide additions to the tank water, almos 24 hours later the effect still remains.
This one (posted earlier) was done at ~an hour after putting the probe in the tank.

after 16 hours in the tank, repeated with same result (half the peroxide - didn't feel like slamming the tank with too much h2o2)

Then one more time at 22 hours in the tank...

So neither scrubbing, tap water rinse, a day in the tank, or 3 doses of peroxide undid the "pre-conditioning" of 1/100 diluted bleach.

I then soaked the probe in 1/10 diluted Prime (thiosulfate-like) for 20 min. Then rinse, scrub, back in the tank for an hour and the next h2o2 dose made the ORP jump (+20mV) up instead of down. No pic of that data.

Excellent. You can turn the effect “on” and “off”and reproducibly. If someone can confirm your findings, I’d say it is time publish!

I am working on replicating this work...Got started a little later than expected....

 

[Lasse]

My question - if you will let this electrode rest for a day or two - put it in the DT and try to reproduce the result. Interesting to know if the bleach give a persistent effect or not.

Sincerely Lasse

 

[Randy Holmes-Farley]

Here's the data follow up, after "pre-conditioning" my probe in dilute bleach, 3 repeated peroxide additions to the tank water, almos 24 hours later the effect still remains.
This one (posted earlier) was done at ~an hour after putting the probe in the tank.

after 16 hours in the tank, repeated with same result (half the peroxide - didn't feel like slamming the tank with too much h2o2)

Then one more time at 22 hours in the tank...

So neither scrubbing, tap water rinse, a day in the tank, or 3 doses of peroxide undid the "pre-conditioning" of 1/100 diluted bleach.

I then soaked the probe in 1/10 diluted Prime (thiosulfate-like) for 20 min. Then rinse, scrub, back in the tank for an hour and the next h2o2 dose made the ORP jump (+20mV) up instead of down. No pic of that data.

Curious.

What is the electrode probe material supposed to be?

 

[taricha]

Curious.

What is the electrode probe material supposed to be?

https://www.vernier.com/product/orp-sensor/

"

• Type: Sealed, gel-filled, epoxy body, Ag/AgCl reference
• Redox potential range: -450 to +1100 mV
• ORP element: 99% pure platinum band sealed on a glass stem"

 

[taricha]

My question - if you will let this electrode rest for a day or two - put it in the DT and try to reproduce the result. Interesting to know if the bleach give a persistent effect or not.

Yeah. Interesting question.
The bleach effect (making my probe act like everyone else's) seems to be persistent over a day at least in the display. But pre-conditioning in thiosulfate may not be as persistent - the upward ORP move when adding h2o2 may not stick around from one day to the next. Looking into that.

When you say "rest" do you just mean leave it in the display? Because the storage solution (3.5M KCl) creates a different effect - as though it's a reducer.

 

[DrZoidburg]

Agreed most are precious metals or pm alloys if lab grade that is. @Randy Holmes-Farley

 

[DrZoidburg]

@Lasse did not read whole thread yet. Have you tried a strong acid to clean probe? This could make results more sensitive.

 

[Lasse]

That´s next step in a month or two - this is a long time investigation

Sincerely Lasse

 

[taricha]

How connect these results with @taricha ´s result with "pre-conditioning"? Note -that I have stopped my oxidator since I started this test in the DT.

If in fact there are deposits on our probe that react with peroxide, then consistent with the effect we see, we might guess that their state under normal tank conditions is mostly oxidized, and when h2o2 is present some of the deposits get reduced.

When the peroxide dissipates under normal conditions most of that material in the deposits that got reduced will revert back to oxidized.

(I have no idea if that's true, only that I think it would fit our observations.)

 

[Dan_P]

If in fact there are deposits on our probe that react with peroxide, then consistent with the effect we see, we might guess that their state under normal tank conditions is mostly oxidized, and when h2o2 is present some of the deposits get reduced.

When the peroxide dissipates under normal conditions most of that material in the deposits that got reduced will revert back to oxidized.

(I have no idea if that's true, only that I think it would fit our observations.)

Does persulfate now cause a dip like H2O2 after treating your ORP electrode?

Trying to sort out this effect. Is it a general peroxide effect or a specific H2O2 effect?

 

[taricha]

Does persulfate now cause a dip like H2O2 after treating your ORP electrode?

Trying to sort out this effect. Is it a general peroxide effect or a specific H2O2 effect?

Don't know. I'll check it in a day or two.

 

[Randy Holmes-Farley]

https://www.vernier.com/product/orp-sensor/

"

• Type: Sealed, gel-filled, epoxy body, Ag/AgCl reference
• Redox potential range: -450 to +1100 mV
• ORP element: 99% pure platinum band sealed on a glass stem"

It will have organics attached to it, and those may be impacted by oxidizers and reducers:

Adsorption of an organic film at the platinum-seawater interface

https://images.peabody.yale.edu/publications/jmr/jmr35-02-03.pdf

"The data were consistent with adsorption of an organic film from the natural water samples onto the metal surfaces. The thickness of the film increased over a period of hours according to ellipsometric measurements and it was not removed by washing in organic-free water. The film on platinum was electrophoretically similar to that previously found on a number of nonconductors"

 

[Dan_P]

It will have organics attached to it, and those may be impacted by oxidizers and reducers:

Adsorption of an organic film at the platinum-seawater interface

https://images.peabody.yale.edu/publications/jmr/jmr35-02-03.pdf

"The data were consistent with adsorption of an organic film from the natural water samples onto the metal surfaces. The thickness of the film increased over a period of hours according to ellipsometric measurements and it was not removed by washing in organic-free water. The film on platinum was electrophoretically similar to that previously found on a number of nonconductors"

Very nice reference.

It also gives me a possible simple method of using a mirrored surface and reflected light to measure biofilm growth and maybe spectral characteristics of the film. One possible application would be to quantitate biofilm growth on aquarium glass. Thanks.

 

[taricha]

"The data were consistent with adsorption of an organic film from the natural water samples onto the metal surfaces. The thickness of the film increased over a period of hours according to ellipsometric measurements and it was not removed by washing in organic-free water. The film on platinum was electrophoretically similar to that previously found on a number of nonconductors"

Nice.
Thinking about removal (to confirm the effect is external film/deposits).
I'm thinking toothbrush +
1) detergent
2) then if that doesn't work maybe solvent (ethanol)
3) then if that still doesn't remove the effect, acid (HCl or H2SO4)