pH probe recovery experiment

[Randy Holmes-Farley]

How long do you think it might take to rehydrate 50 nanometers of glass?

I have no idea.

 

[PedroYoung]

I sell industrial pH sensors for a living and my experience had been that after drying out, rehydrated pH glass can respond to changes in pH but usually with significant time lag. I normally say to rehydrate in a 4 pH buffer overnight and then test (then call me and order a spare haha).

 

[piranhaman00]

20$ probes from Amazon work great and last over a year

 

[Randy Holmes-Farley]

20$ probes from Amazon work great and last over a year

What’s the fun in that? lol

 

[stenopus]

is there anyone who can suggest which probe to get for my GHL kh director? Genuine one cost more than 130 EUR.. Mr. Randy?

 

[Randy Holmes-Farley]

is there anyone who can suggest which probe to get for my GHL kh director? Genuine one cost more than 130 EUR.. Mr. Randy?

If the cord ha a standard bnc connector in it, then you can pick any pH probe with a bnc connector.

Here’s my generic recommendation, but note the specific probe recommendation is old and likely not sold still.

Selection of Combination pH Electrodes​

There are hundreds of different types and styles of pH electrodes. These vary in size, composition (glass or plastic sides, typically), shape, the nature of the glass membrane (even non-glass materials can be used), how that membrane is separated from the internal filling solution, (that is, single vs. double junction), whether the internal fluids are sealed or refillable, and a variety of other issues.

For most reef aquarists, the exact nature of the pH electrode doesn’t much matter. Nearly all can give suitable pH readings. Here is my opinion about what is most important to look for:

1. Selecting an epoxy body electrode instead of a glass body electrode will make it less likely that you will break it by accident. The glass bulb on the tip is still very fragile (I’ve broken many), but the bulb can be protected by a plastic shield to reduce the chance of breakage.
2. If you intend on measuring pH directly in the aquarium or sump (rather than in a cup of water removed from the aquarium), then expect to occasionally get the whole electrode wet (by accident). If it is a refillable type which has a hole for adding more filling solution (usually KCl), then you might get aquarium water into the electrode. That can severely degrade performance by messing up the reference electrode. So selecting a sealed electrode may be a better choice.
3. Some folks argue that a double junction electrode is preferable, and that is likely true. Without going into the design details, a double junction electrode makes it much less likely that there will be any exchange of ions between the aquarium and the filling solution through the glass bulb. This option may be especially important if you are using an internal reference electrode other than Ag/AgCl. For example, if it is a calomel reference electrode, it contains mercury. It is desirable to keep mercury salts out of the aquarium due to its toxicity, so a double junction is likely preferable in that case. Likewise, it is desirable to keep sodium and other seawater ions from entering the reference electrode, and a double junction prevents that to a much greater extent than a single junction. That aspect is more important if you leave the electrode in the aquarium water than if you put in into a storage solution after every use. In general, it is likely better to have a double junction
   than a single junction, but it may not result in appreciably better measurements.
4. There are other attributes of certain electrodes that may make them more useful in laboratories, and hence justify prices that easily range to more than $350 for the electrode alone. There is not likely any significant advantage in using such electrodes for reef aquaria, however. Do not be worried about claims that you need a special electrode for high pH or high sodium environments. That is true for the most accurate measurements at high pH and high salinity, but aquarium water will be OK with a standard electrode, and even brief measurements at high pH (like limewater) will be fine.

An electrode that I have been using for the past few years is sold by Cole Parmer. It is catalog number U-59001-70. It has an epoxy body, is sealed, and has a double junction. I’m not certain what type of reference electrode it contains, but I believe it to be Ag/AgCl. Its list price is $60.

Aquarium Chemistry: Measuring pH with a Meter

This article describes how pH meters work, how to select one to use, and how to best use it to measure the pH of a reef aquarium.

reefs.com

 

[stenopus]

its the same: €127.11EUR / Each

 

[Rollnwthdatide]

When I took down my tank 8 years ago, I got rid of nearly everything. One thing that remained in the fish room cupboard is a ceramic mug containing a bunch of pH probes, some of which are pretty high end. For example, two are Ross pH electrodes. Fisher Scientific currently is selling them for $722 each (I didn't originally buy them, but got them used from places I worked for that no longer needed them).

Orion™ 8102BNUWP ROSS Ultra™ pH Electrode

Conduct precise pH determinations with this general purpose, top performance glass body combination electrode with waterproof BNC connector.

www.thermofisher.com

Once upon a time they were in some type of water in the mug. I don't recall what it was. Maybe tank water, but probably tap water.

A couple of weeks ago, I went to figure out if anything was salvageable. I tried to pick up the mug by the handle and the mug literally broke into a dozen pieces. Of all the things I thought I might find, that was not among them. It was from a family reunion long ago. They probably bought the cheapest mugs available. lol

Of course, there was no water left, just dried salts. Even inside the probes they looked entirely dried out.

The glass bulb of a typical pH probe is a very important piece of hydrated thin glass that allows measurement of pH. The way it does that is surprisingly complicated, and I discuss it here for anyone interested in more details:

Aquarium Chemistry: Measuring pH with a Meter

This article describes how pH meters work, how to select one to use, and how to best use it to measure the pH of a reef aquarium.

reefs.com

This little section from it summarizes the effect:

The glass used in a pH electrode has a composition that includes certain metals in addition to the usual silicon and oxygen of SiO2 glass. These metals can include lithium, barium, lanthanum, sodium, and calcium, among others. At both the inside and outside surfaces of the glass bulb (and also in a thin (50 nm) swollen region of hydrated glass on each side), there is some substitution of H+ for these cations. How much substitution depends on how much H+ is in solution, and hence on pH. The internal pH does not change, but the external pH does, so the amount of substitution on the outer surface changes while on the inside it does not, setting up a potential difference across the glass membrane that depends on pH.

Note in that description is the mention of a hydrated layer on the glass. That is why one does not want them to dry out. A pH electrode that has been sitting dry for years has certainly changed the nature of the hydrated glass, and it may well never be recoverable.

But why not try?

So this is a long term experiment to see if I can get any of these probes suitably working again.

First step was to refill the insides of them. All (IIRC) were refillable through a hole in the body. Some pH electrodes are sealed, but not these. I only had one filling solution available (also sitting on the fish room shelf). Some different pH electrodes use different filling solutions, but I'm not sure what happens if they are not exactly matched. Most are a fairly concentrated potassium chloride solution, and some are saturated with silver chloride as well. I think it was a Ross filling solution I used, but I'll have to double check that.

After filling them all, the next step was to try to rehydrate them on the outside. I'm not sure if that will work or how long it might take. I placed them all into a container of tap water and started them off soaking.

In the near future, I'll be seeing if I can get an old pH meter working again (found a meter behind a box in the old fish room but so far, not the cord lol) and then see if these are at all responsive to pH.

Assuming they do respond to pH, then I'll see if they can be used with actual calibration fluids to give useful values.

So no answers yet, just a long slow work in progress.

Happy reefing.

So i have a BlueLab pH pen for some growing that I do. They use a KCl storage solution and just say that if the tip does dry, then to rehydrate in the KCl solution for 24-48hrs. I calibrate after and it's worked fine for me.

I had some old back up pH probes that were unused but stored for the last 6yrs from my reefing break. I should've tried to rehydrate them and see if they still worked.

 

[Troylee]

Randy dropping more hints he’s setting up a tank… this is clue number 2

 

[Malcontent]

Someone on reddit was trying to rehydrate a TDS meter...

 

[Randy Holmes-Farley]

Someone on reddit was trying to rehydrate a TDS meter...

That would be interesting. lol

 

[vahegan]

is there anyone who can suggest which probe to get for my GHL kh director? Genuine one cost more than 130 EUR.. Mr. Randy?

I replaced mine with Cole Parmer, but you can use PinPoint too, it is easier to get and more affordable, about $46 on Amаzon.

 

[Miami Reef]

I believe the effort is worth it. This isn't just a pH probe—it's a meticulously crafted instrument, almost a work of art. When you're an expert chemist, you naturally appreciate the finer tools of the trade, like a connoisseur appreciates fine wine. lol

 

[Randy Holmes-Farley]

Well, interim update looks good.

Found a cord in my cord drawer and the Orion 410A pH meter powered up. The meter has a manufacture date of 1993 on it. lol

Picked one pH probe with a cover on the bnc connector so it wasn’t corroded (one was blue and scuzzy lol).

Pried the bnc connector cover off with pliers and hooked it up. Reads pH 10.0 in lemon scented ammonia cleaner and pH 3.4 in ascorbic acid in water, so it clearly is responding to pH.

Time to buy or make some actual calibration buffers and try them all
out!

 

[Garf]

Time to buy or make some actual calibration buffers and try them all
out!

Citric acid and citrate?

 

[Miami Reef]

Wow. That’s quick!

If you have Borax laying around:

Craig Bingman talks about that standard here;

Aquarium Frontiers Biochemistry of Aquaria

It also turns out that the pH of borax solutions is only weakly dependent on the concentration of borax in the solution. So, we don’t need to be tremendously precise in our measurement of the borax to still produce a useful pH standard.

 

[rishma]

Reads pH 10.0 in lemon scented ammonia cleaner

lol