Storing Omega PHH-7000 meter

I bought this and it seems like a nice little meter.

It came with a wee little bottle of storage solution and a bottle of 7 and 4 solution.

I emailed the company about the storage solution as they did not have any listed on their web site and it the forums here seem to suggest using the storage solution from the manufacturer.

They replied saying to store it in 7 or 4 solution rather than a particular "storage solution".

Has anybody else heard of this or does that seem "ok".

In the forums here the recommendation is to store it in what the manufacturer tells you to store it in. See https://www.homebrewtalk.com/showthread.php?t=302256

I'm constantly amazed at recommendations by manufacturers that have little basis. It's as if the marketing department were authoring the recommendations instead of a technical department.

The primary objective of a storage solution is to keep the glass membrane hydrated. That can be accomplished via a drop or two of distilled water in a sealed cover over the probe. However, if a user mistakenly fills that sealed cover with distilled water that is in contact with the glass membrane, then the result can be that the electrolyte in the probe can diffuse out of the probe and into that water...lost from the probe. Repeated application of distilled water can essentially 'drain' the probe of it's ionic content. This result is an easily understood occurrence since: "if a little is good, a lot is better" and the user overfills the sealed cover. The important factor here is that you DON'T want to put too much water in there. That drop of water is to provide humidity, not saturation.

Other manufacturers do recommend storing probes in ionic solutions that are often composed of potassium chloride at molar strength between 1 and 3. In their case, the solution should be in contact with the glass membrane.

Unfortunately, ANY manufacturer that recommends storing their probe in pH 4 or 7 solution apparently doesn't understand the chemistry and physics involved in pH probes. Those solutions will eventually deplete the probe of its electrolyte and leave you with a prematurely inoperative probe. Bad for you, but good for the manufacturer since you have to buy a replacement.

Don't let the marketing department cost you money.

mabrungard said:

I'm constantly amazed at recommendations by manufacturers that have little basis.

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I am equally amazed that Martin has the temerity to assume he knows more than the manufacturer does about his product. Does Martin know what kind of sense electrode is used? Does he know what the junction technology is? Does he know how the soaker bottle functions? There have been occasions in a fairly long engineering career where I found I understood some aspect of an instrument better than its manufacturer (and the savvy ones would come to us to see what they could learn about improving their devices and how they were used) but it was pretty rare.

I agree that if the junction is the common frit or the now even more common rag type that DI water or a pH buffer in contact with the junction might not be the best way to go for the reasons mentioned. I don't presume to know how this meter is made or what is the best way to store it but it appears (from the photo) that the soaker cap is designed to hold but a drop or two of the soaker solution provided by Omega in order to keep the bulb (and it does appear from the photograph to be a bulb sensor) wet. Is there perhaps a sponge in the bottom of the bottle? I have seen that done. If my interpretation is correct then the junction would not be immersed, whatever its design, and it would indeed be fine to store with distilled water, tap water or a buffer (better the buffer as it will keep the ion balance in the hydrated layer close to what it is in operation). This is, broadly, the way the new Hach pocket meter is stored i.e. the junction is not in contact with the storage 'solution' which can be tap water, DI water or no water at all (modern sensor glass does not need to be stored hydrated - it hydrates very rapidly). I still like to keep it from drying out - probably because of habit as much as anything else.

My advice does not change: do what the manufacturer tells you to do and that is spelled out (though not very clearly) in the manual. It says to keep the soaker bottle wet, to put it over the electrode and then put the cap over that. This should keep things wet inside for a long time and, presumably, the contents of the soaker bottle solution should last for a long time but clear the OP wants to know what to do when it runs out if it runs out before the end of life of the electrode. If OP thinks Martin is smarter than Omega then, of course, he should follow Martin's advice and use something other than pH4 or pH7 buffer. But Martin withheld the most important piece of information from him and that is what to use instead of 4 or 7 buffer. If OP thinks Omega is smarter than Martin (on this subject) then he should follow manufacturers advice.

I would, however, look into this a little further as one has to wonder why, if a buffer is entirely suitable as the moistener in the soaker cap, they don't just instruct one to use a drop of buffer instead of the soaker solution. I would look carefully at the bottle for a part number if there is one and then tell Omega you want to order that part number. Or, if there is no part number, call back at a later date and say you are almost out of soaker solution and need to order more to see if you get the same story. It is possible to get someone in customer support or sales who has misinformation about a product or, if this is a new product developed far enough to be released but still being tweaked engineering may change its mind about the best protocol for storage. There is as much art in pH electrode design and manufacture as science.

The other thing to do is to see if ingredients are listed on the bottle. If it says "distilled water and buffers" then you are doubtless OK. If it says 3M KCl, saturated AgCl then you know that what the manual says and what tech support said are in conflict.

mabrungard said:

The primary objective of a storage solution is to keep the glass membrane hydrated. That can be accomplished via a drop or two of distilled water in a sealed cover over the probe.

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The primary objective of a storage solution was to keep stuff in the reference half cell in the reference half cell. In recent times the most popular reference electrode was the silver/silver chloride electrode in a solution of saturated silver chloride and potassium chloride. It had lots of desirable properties like nearly constant emf with temperature. In a typical combination electrode the electrode 'solution' was a gel of some sort and the chamber that held it typically communicated with the sample through a glass frit which allowed some solution to pass between the interior of the electrode and solution being measured thus completing the electrical circuit. Twenty to thirty years ago if you had a problem with your pH electrode I could tell you what it was without knowing anything more than that you had a problem. It was fouling of the junction. A solution to that problem was often to have the reference chamber communicate through the frit not to the sample but to another chamber filled with another electrolyte that didn't foul when exposed to the sample to the extent that silver chloride does (complexes with proteins) and have that chamber communicate with the sample through another frit, a ground glass stopper or some other means. This is the double junction design that is still used today though not so much so as there have been dramatic improvements in junction design. In any case the storage solution is a solution that is so close to the composition of the fill solution that there is no tendency for either ions or solvent (water) to pass from the electrode to the fill solution. If the fill solution is saturated with silver chloride and potassium chloride it is a pretty good hint that this is what the reference electrode is filled with. Thus the principle function of the storage solution is to keep the reference fill in the reference electrode. In the older electrodes hydration took time but now seems to be much faster so hydrating the membrane becomes a secondary function.

mabrungard said:

However, if a user mistakenly fills that sealed cover with distilled water that is in contact with the glass membrane, then the result can be that the electrolyte in the probe can diffuse out of the probe and into that water...lost from the probe.

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Follow the manufacturer's instructions and you wont do that. Also don't pull on the glass bulb with Vice Grips. You will break it.

mabrungard said:

Other manufacturers do recommend storing probes in ionic solutions that are often composed of potassium chloride at molar strength between 1 and 3. In their case, the solution should be in contact with the glass membrane.

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It needs to be in contact with at least the reference junction and, in electrodes where hydration of the membrane is required or of benefit, both junction and membrane, for the reasons discussed above. It would be hard to imagine a configuration in which it contacted the reference junction without contacting the bulb, however.

mabrungard said:

Unfortunately, ANY manufacturer that recommends storing their probe in pH 4 or 7 solution apparently doesn't understand the chemistry and physics involved in pH probes.

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At this point my money is on the manufacturers.

I'm sorry if all this seems acerbic but I think advising people to ignore the manufacturer's instructions is just really bad advice in the great majority of cases.

This is where knowledge of chemistry and physics is an important skill and the ability to assess when things just don't seem right. I know that AJ has all of that and more, but he chose to ignore his own knowledge in accepting that Omega's information recommends storing the probe in calibration solutions. Unless the laws of chemistry and physics have changed, I'm pretty sure that AJ knows that very low ionic strength solutions such as distilled water and calibration solutions will impose an osmotic stress on the sensor and start to leach whatever ionic content out.

I just reviewed Omega's instructions and they do not recommend using the calibration solutions, but do say to use their soaker solution as you mention. The key here is that someone may read that initial post and opine that calibration solutions are OK. I will continue to state that they are not, unless they are applied as a drop or two in the storage cap to keep the bulb environment humidified. So, my money was not on the manufacturer's instructions and it turned out that I was correct (because the manufacturer does not recommend storing in calibration solution). At least I could decipher that something may not be right.

I will concur that blind application of my recommendations may not be wise when dealing with the newest junction technology. However on this forum, the vast majority of users are hobbyists that are much more likely to be employing more 'value-priced' equipment that uses tried and true junction technology. So you caught me stating absolutes when I should have been stating generalities. But my point was to get users to think twice about recommendations. While companies like Omega, Oakton, and Hach have very capable technical staff, there are plenty of 'budget' level sellers that have none of that and it very well could be some truly uninformed person formulating recommendations. So let's not assume that the manufacturer is always correct. I believe you state the same above.

mabrungard said:

This is where knowledge of chemistry and physics is an important skill and the ability to assess when things just don't seem right. I know that AJ has all of that and more, but he chose to ignore his own knowledge in accepting that Omega's information recommends storing the probe in calibration solutions.

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Their manual says store it using the provided soaker solution. OP was told that he could use buffers. I accept that OP told the truth about what Omega told him. My (limited) knowledge of the chemistry of pH measurement tells me that this is fine if the storage liquid does not reach the reference frit as I explained at length in the previous post.

mabrungard said:

Unless the laws of chemistry and physics have changed, I'm pretty sure that AJ knows that very low ionic strength solutions such as distilled water and calibration solutions will impose an osmotic stress on the sensor and start to leach whatever ionic content out.

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I perfectly well know this and also know that it is necessary for the formation of what Galster ["pH Measurement Fundamentals, Methods, Applications, Instrumentation" VCH, Weinheim 1991] referrs to as the 'leached layer'. Alkali metal ions must be leached out of the membrane and replaced by hydrogen ions in order for the membrane to load up with OH- ions. It is the redox involving OH- in the glass and H+ in the sample that sets up the membrane potential. You should think in terms of chemical potentials rather than 'osmotic stress'. Osmotic pressure is a result of the difference in chemical potential of the solvent between the sample and the interior of the bulb. Since the interior of the bulb contains dilute hydrochloric acid and the sample is a fairly dilute solution of sugars osmotic pressure is not of concern. What is of concern is the relative chemical potential of ions like sodium and lithium (a common dopant for pH sensing glass) in the glass (relatively high) and the storage solution. Assuming we are talking a typical storage solution it contains KCl and AgCl. No Na+ or Li+ and therefore there is a chemical potential gradient from glass to solution. These ions therefore migrate from the glass to the solution thus forming the leached layer. It is, therefore, fine to store the electrode in water of low chemical potential of lithium and sodium ions. You would not want to store it in a buffer or other solution that contains sodium, though.

Let me be perfectly clear that in saying all this I am talking about typical construction of electrodes around the turn of the century. There have clearly been improvements in the art since then and as I don't know what they are I can't assert that what I have put in the preceding paragraph is applicable in all cases as I don't know what the details of the modern designs or glass recipes are. But the manufacturer does. Readers would be well to heed the manufacturers advice therefore.

mabrungard said:

I just reviewed Omega's instructions and they do not recommend using the calibration solutions, but do say to use their soaker solution as you mention.[/QUOTE Check

mabrungard said:

The key here is that someone may read that initial post and opine that calibration solutions are OK. I will continue to state that they are not, unless they are applied as a drop or two in the storage cap to keep the bulb environment humidified.

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Yes, they are OK if you follow the manufacturers instructions.

mabrungard said:

So, my money was not on the manufacturer's instructions and it turned out that I was correct (because the manufacturer does not recommend storing in calibration solution).

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Yes, he does. That is what he told OP to do on the phone if he didn't have any more soaker solution.

I can't find much right in statements like

"recommendations by manufacturers that have little basis"

"The primary objective of a storage solution is to keep the glass membrane hydrated."

"if a user mistakenly fills that sealed cover with distilled water that is in contact with the glass membrane, then the result can be that the electrolyte in the probe can diffuse out of the probe and into that water...lost from the probe. Repeated application of distilled water can essentially 'drain' the probe of it's ionic content"

"Unfortunately, ANY manufacturer that recommends storing their probe in pH 4 or 7 solution apparently doesn't understand the chemistry and physics involved in pH probes."

It seems you are confusing the sense bulb half cell and the reference half cell as solutions low in potassium, chloride, and silver can cause those to migrate out of the reference half cell and water to migrate in (I've seen that happen).

mabrungard said:

At least I could decipher that something may not be right.

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The only thing that is disturbing here is that they furnish a storage solution which suggests that it is superior, for whatever reason, to a buffer (unless, of course, that is what it is) and don't seem to make a replacement for this available. Nor do they explicitly state in the manual that buffer is an acceptable replacement. While they do say to use the storage solution to keep the storage bottle wet they do not explicitly warn against overfilling it

mabrungard said:

I will concur that blind application of my recommendations may not be wise when dealing with the newest junction technology. However on this forum, the vast majority of users are hobbyists that are much more likely to be employing more 'value-priced' equipment that uses tried and true junction technology.

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Most are moving to the newer technologies. Those who are using older meters should follow the manufacturers instructions just as those using the newer meters should.

mabrungard said:

'budget' level sellers that have none of that and it very well could be some truly uninformed person formulating recommendations.

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If some manufacturer is putting out bad advice, and by bad I mean advice that has a real detrimental effect on the performance of the equipment he is selling then the market will note that and his sales will drop. That's how capitalism works.

Obviously we address lots of questions about pH meters here. How many instances have we had where the problem turned out to be that the manufacturer advised storage in buffer or distilled water when that was not the right way to store the meter? Who knows. Maybe this Omega meter will be the first!

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I know this is an old thread, but I have run into the same issue with Omega. Their tech folks confirmed that when the ‘soaker’ solution is gone, I am to use 4 or 7 buffer. I did order a new probe, and notice large bubbles midway up. I think this is indeed a case where the solution is to just wet the bulb, not cover it. So I guess I will go with their direction for storage. Any updates on this?