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

[Rick Mathew]

Lasse adds H2O2 to new Red Sea saltwater (new probe) not much effect - no big ORP drop.
I add H2O2 to new Instant Ocean saltwater (probe from storage) - no big ORP drop (a small rise in fact).
Rick adds H2O2 to new Red Sea saltwater (old probe) big ORP drop just like in tank water.

Seems evidence for the large drop effect being mostly super-local to the probe. Either biofilm, or internal conditioning.

Are all of the probes constructed in the same way?

Rick

 

[Rick Mathew]

Lasse adds H2O2 to new Red Sea saltwater (new probe) not much effect - no big ORP drop.
I add H2O2 to new Instant Ocean saltwater (probe from storage) - no big ORP drop (a small rise in fact).
Rick adds H2O2 to new Red Sea saltwater (old probe) big ORP drop just like in tank water.

Seems evidence for the large drop effect being mostly super-local to the probe. Either biofilm, or internal conditioning.

What is interesting to me is I saw that large drop with my first dose of 3% (290-262) but hardly any response when dosing 12% H2O2 at the very end of the test...not what I expected

 

[Randy Holmes-Farley]

What is interesting to me is I saw that large drop with my first dose of 3% (290-262) but hardly any response when dosing 12% H2O2 at the very end of the test...not what I expected

Maybe it had already reduced all of the easily reduced substances.

 

[Dan_P]

My old Redox probe - biofilm ..... he he he he. Its a living system

​

It is cleaned with a toothbrush now - not sterilized. That will be next step

Sincerely Lasse

You have created a unique sensing device, part biological part physical.

 

[Dan_P]

I agreed that there is some point in low concentration where adding an oxidizer or reducer to seawater will have no detectable effect. Since neither of us knows what level that is, I think trace metal speciation changes caused by H2O2 remains a perfectly viable explanation. There may also certainly be other explanations.

I like the transition metal effect and agree it is among the likely explanations.

 

[Rick Mathew]

Maybe it had already reduced all of the easily reduced substances.

Most likely...

 

[Dan_P]

What is interesting to me is I saw that large drop with my first dose of 3% (290-262) but hardly any response when dosing 12% H2O2 at the very end of the test...not what I expected

@Lasse uses an Oxydator in some or all of his systems. I wonder if the small continuous dose of H2O2 plays a similar role in diminishing the “H2O2 dip” when he adds a bolus of peroxide to those systems.

I am waiting to see what @taricha finds when he doses persulfate to a water sample.

 

[taricha]

Are all of the probes constructed in the same way?

Nope. You and Lasse likely have almost identical probes (double junction) for saltwater hobby usage.
I have a single junction educational probe.

What is interesting to me is I saw that large drop with my first dose of 3% (290-262) but hardly any response when dosing 12% H2O2 at the very end of the test...not what I expected

Dan found that h2o2 persists longer than you'd think in saltwater (but substrate gets rid of it pretty fast). So a bunch more in addition to some already there will show a tiny effect, likely for the reason that Randy said. It's already interacted with most of the things that it can affect (and that ORP can measure).

I am waiting to see what @taricha finds when he doses persulfate to a water sample.

You haven't even gotten your Fe + I.O. data from me yet. Nor the Cu in distilled water

 

[Dan_P]

Nope. You and Lasse likely have almost identical probes (double junction) for saltwater hobby usage.
I have a single junction educational probe.


Dan found that h2o2 persists longer than you'd think in saltwater (but substrate gets rid of it pretty fast). So a bunch more in addition to some already there will show a tiny effect, likely for the reason that Randy said. It's already interacted with most of the things that it can affect (and that ORP can measure).



You haven't even gotten your Fe + I.O. data from me yet. Nor the Cu in distilled water

It’s excruciating experiencing scientific discovery vicariously

 

[taricha]

It’s excruciating experiencing scientific discovery vicariously

Here's your Ferrous Sulfate addition to I.O.

This is the parallel version to the Cu additions to I.O. done in this post.....

One subsample is just H2O2 added to the I.O., the second was me adding 10ppb Cu to the I.O. before H2O2. The third is an addition of 30ppb Cu to the I.O. before H2O2.

okay, I let things equalize longer and the story is ... different than Copper, and not just a mirror image.
Yellow line is I.O. only.
Blue Line is I.O. +10ppb Fe (stock made from ferrous sulfate heptahydrate)
Red line is I.O. +30ppb Fe

You can clearly see where the Fe stock was added and where the H2O2 went in.
The initial drop may be expected due to the Fe(ii) form of the iron going in. It seems to get oxidized and return the sample to the normal ORP in 30 min or so. Then the H2O2 additions raise the ORP but very very similarly, not responsive to the added 10 and 30ppb Fe. The final h2o2 addition in the red data is me realizing I goofed and did not confirm that more h2o2 wouldn't push the ORP further. In other words it's possible that the results were the same because the h2o2 was the limiting reagent so to speak. But adding double the h2o2 didn't dramatically change the story.
Likely this is a result of the Fe being added in the 10ppb range is not dramatically different than the amounts present in the salt mix already.
What is clearly different is that the Fe(ii) has a big temporary effect until it gets oxidized to match the I.O. ORP by simply mixing.

 

[Dan_P]

Here's your Ferrous Sulfate addition to I.O.

This is the parallel version to the Cu additions to I.O. done in this post.....



okay, I let things equalize longer and the story is ... different than Copper, and not just a mirror image.
Yellow line is I.O. only.
Blue Line is I.O. +10ppb Fe (stock made from ferrous sulfate heptahydrate)
Red line is I.O. +30ppb Fe

You can clearly see where the Fe stock was added and where the H2O2 went in.
The initial drop may be expected due to the Fe(ii) form of the iron going in. It seems to get oxidized and return the sample to the normal ORP in 30 min or so. Then the H2O2 additions raise the ORP but very very similarly, not responsive to the added 10 and 30ppb Fe. The final h2o2 addition in the red data is me realizing I goofed and did not confirm that more h2o2 wouldn't push the ORP further. In other words it's possible that the results were the same because the h2o2 was the limiting reagent so to speak. But adding double the h2o2 didn't dramatically change the story.
Likely this is a result of the Fe being added in the 10ppb range is not dramatically different than the amounts present in the salt mix already.
What is clearly different is that the Fe(ii) has a big temporary effect until it gets oxidized to match the I.O. ORP by simply mixing.

The plot thickens, though the subtitles of this movie are in binary

Thinking about @Rick Mathew results: add an oxidizer and the solution is reduced, i.e., the H2O2 dip. H2O2 gives up electrons when it is converted to O2 and water. Conjecture 1: H2O2 dip is the decomposition of H2O2. Why does the second H2O2 addition fail to elicit the dip? What facilitated the the decomposition of H2O2 was consumed (See @Randy Holmes-Farley idea above) This might be where the transition metal effect comes into play. If it was an enzymatic decomposition, I don’t see it petering out by the second addition. I wonder how long it takes Rick’s system to recover.

Conjecture 2: H2O2 forms reactive oxygen species before it can be destroyed and lyses cells. Your Fe(II) additions suggest cells dumping their iron stores could cause a dip. I have no idea whether just organic matter from lysed cells would have such a strong effect. Why does a second addition of H2O2 fail to produce the same effect? The lysed cell contents catalyze the decomposition of H2O2 and no further cell lysis occurs. This seems to contradict Conjecture 1, decomposition of H2O2 causes the dip. The conjecture explains no dip in fresh IO and a dip in aquarium water. The notion fails to cover your aquarium water observations where there is a H2O2 rise instead of a dip.

Thanks for this evening’s data fix.

 

[taricha]

Conjecture 1: H2O2 dip is the decomposition of H2O2

Lasse earlier introduced potato to his Tapwater to see if enzymatic decomposition of the h2o2 was the driver for a big ORP move and nothing happened (post 12)

Here's an idea. It's complicated and doesn't rise to the level of conjecture.

In newly mixed saltwater there are a number of ORP-affecting species present in relevant amounts. In distilled water almost none. So ORP is "unbuffered" (so to speak), and a tiny addition of Fe or Cu to RODI ought to move the ORP a lot, and the addition of h2o2 ought to similarly move the ORP a ton if there's only one of these affected metals around, because there's little else to "buffer" it.
Now, what if in the biofilm - instead of it being the case that there's a bunch of ORP-affecting species, what if instead there are very few... because the organics have caused the transition metals to be less susceptible to h2o2 oxidation.
From Randy's reference
"In fact, these authors also highlighted the key role of H2O2 and O2− in the redox cycling and how the organic ligands reduced the reactivity of Fe and Cu. Heller and Croot, 2010, Heller and Croot, 2011 demonstrated the importance of organic chelation of Fe and Cu in controlling the reactivity with superoxide, where copper seems to be the major sink for superoxide. Both Fe and Cu speciation are dominated by organic species (Campos and van den Berg, 1994, Coale and Bruland, 1988, Moffett, 1995, Gledhill and van den Berg, 1994, Rue and Bruland, 1995, Wu and Luther, 1995), mostly produced by phytoplankton or bacteria increasing the solubility of these metals. Indeed, the interaction between Fe and Cu for the humic ligands in natural waters has been reported by Abualhaija et al. (2015)."

So in that biofilm environment, with most ORP-affecting substances in some sort of relationship with organics, there may instead be a much smaller playing field for ORP, and like in RODI water - tiny changes can cause big moves.


Edit: striking out some of that. Measurements in RODI don't support that idea.

 

[Dan_P]

Lasse earlier introduced potato to his Tapwater to see if enzymatic decomposition of the h2o2 was the driver for a big ORP move and nothing happened (post 12)

Here's an idea. It's complicated and doesn't rise to the level of conjecture.

In newly mixed saltwater there are a number of ORP-affecting species present in relevant amounts. In distilled water almost none. So ORP is "unbuffered" (so to speak), and a tiny addition of Fe or Cu to RODI ought to move the ORP a lot, and the addition of h2o2 ought to similarly move the ORP a ton if there's only one of these affected metals around, because there's little else to "buffer" it.
Now, what if in the biofilm - instead of it being the case that there's a bunch of ORP-affecting species, what if instead there are very few... because the organics have caused the transition metals to be less susceptible to h2o2 oxidation.
From Randy's reference
"In fact, these authors also highlighted the key role of H2O2 and O2− in the redox cycling and how the organic ligands reduced the reactivity of Fe and Cu. Heller and Croot, 2010, Heller and Croot, 2011 demonstrated the importance of organic chelation of Fe and Cu in controlling the reactivity with superoxide, where copper seems to be the major sink for superoxide. Both Fe and Cu speciation are dominated by organic species (Campos and van den Berg, 1994, Coale and Bruland, 1988, Moffett, 1995, Gledhill and van den Berg, 1994, Rue and Bruland, 1995, Wu and Luther, 1995), mostly produced by phytoplankton or bacteria increasing the solubility of these metals. Indeed, the interaction between Fe and Cu for the humic ligands in natural waters has been reported by Abualhaija et al. (2015)."

So in that biofilm environment, with most ORP-affecting substances in some sort of relationship with organics, there may instead be a much smaller playing field for ORP, and like in RODI water - tiny changes can cause big moves.

A couple more thoughts…

When chelating agents in tank water are an important factor, adding tank water to RODI would diminish the effect in fresh water. Similarly, adding brine to RODI and not diminishing the effect would eliminate salinity as a factor. This last one is important because the sample matrix can play a role in ORP measurements.

 

[Rick Mathew]

The plot thickens, though the subtitles of this movie are in binary

Thinking about @Rick Mathew results: add an oxidizer and the solution is reduced, i.e., the H2O2 dip. H2O2 gives up electrons when it is converted to O2 and water. Conjecture 1: H2O2 dip is the decomposition of H2O2. Why does the second H2O2 addition fail to elicit the dip? What facilitated the the decomposition of H2O2 was consumed (See @Randy Holmes-Farley idea above) This might be where the transition metal effect comes into play. If it was an enzymatic decomposition, I don’t see it petering out by the second addition. I wonder how long it takes Rick’s system to recover.

Conjecture 2: H2O2 forms reactive oxygen species before it can be destroyed and lyses cells. Your Fe(II) additions suggest cells dumping their iron stores could cause a dip. I have no idea whether just organic matter from lysed cells would have such a strong effect. Why does a second addition of H2O2 fail to produce the same effect? The lysed cell contents catalyze the decomposition of H2O2 and no further cell lysis occurs. This seems to contradict Conjecture 1, decomposition of H2O2 causes the dip. The conjecture explains no dip in fresh IO and a dip in aquarium water. The notion fails to cover your aquarium water observations where there is a H2O2 rise instead of a dip.

Thanks for this evening’s data fix.

Dan: Below is a chart of my "After Experiment" Data. It is interesting to note that after Food slurry add the recovery value was 10 points higher than the recover value after the end of the experiment... The 296 value was essentially (294) the value before I took the ORP "Challenge" ..

I am still thinking that OPR is a "quantum entrance" into an alternate universe and @taricha is in a different one

 

[Dan_P]

Dan: Below is a chart of my "After Experiment" Data. It is interesting to note that after Food slurry add the recovery value was 10 points higher than the recover value after the end of the experiment... The 296 value was essentially (294) the value before I took the ORP "Challenge" ..

I am still thinking that OPR is a "quantum entrance" into an alternate universe and @taricha is in a different one

I wear an aluminum foil hat whenever I read @taricha posts to hinder any alien force field escaping his universe. This also cements my resolve never to buy an ORP electrode.

 

[Lasse]

More confusing result.

Even if my probe C (around 25 days in use react to my feedings - it react differently than my old probe A to H2O2 addition.

Probe C

Probe A

The other two Probe B

Probe D

No order at all in the kingdom of sweden
'
Sincerely Lasse

 

[taricha]

Nor the Cu in distilled water

Here's the report on Cu and Fe in distilled water. It's nonsense. My ORP data became so noisy (+- hundreds of mV) that I can't say anything at all except 10ppb Fe(ii) from ferrous sulfate dropped ORP by maybe 100 points in distilled water.

So my analogy with pH (tiny additions in unbuffered solutions give big moves) is not supported.

Edit: striking out some of that. Measurements in RODI don't support that idea

the sample matrix can play a role in ORP measurements.

indeed. subtracting the matrix out was like dividing by zero for my probe.

 

[Dan_P]

What is interesting to me is I saw that large drop with my first dose of 3% (290-262) but hardly any response when dosing 12% H2O2 at the very end of the test...not what I expected

Do you have a plot of the H2O2 ORP dip? If you scaled the plot to the size of your food addition dip, would they be a perfect match?

 

[Dan_P]

Lasse adds H2O2 to new Red Sea saltwater (new probe) not much effect - no big ORP drop.
I add H2O2 to new Instant Ocean saltwater (probe from storage) - no big ORP drop (a small rise in fact).
Rick adds H2O2 to new Red Sea saltwater (old probe) big ORP drop just like in tank water.

Seems evidence for the large drop effect being mostly super-local to the probe. Either biofilm, or internal conditioning.

I am thinking of joining you and @Hans-Werner on the biofilm/electrode conditioning effect.

Since @Lasse has worked very hard trying to reproduce the H2O2 dip and has had equivocal results, the dip seems not to be a water sample property, i.e., the sample ORP did not really change. Your observations add further weight to the notion that we might have been fooled by an electrode There still are tjose internet examples of dips with addition of H2O2 to brine, but we know nothing about the condition of the electrodes in those examples.

I do wonder now if we need to change our investigation into finding a method to reproducibly condition a new or thoroughly cleaned ORP electrode so that it produces well defined dips? Do we need a biofilm or just an organic film? Would a solution of BSA or fish flake extract lay down an electrode modifying film? And where on the probe does this layer have the maximum effect?

Now that I think about it, is this ORP phenomenon only happening in saltwater? Are we looking at a sodium ion effect or a calcium salt deposit?

 

[Lasse]

A little more data. I use a dosing pump in order to dose frozen food during the day. At the evening I rinse the bottle to times around 21:00. 200 ml back and forward two time. My old probe A reacts to this.

Also the oldest of the new ones

There is weak - very weak tendency in the other two as well

Sincerely Lasse