pH Probe Calibration, is it Really Needed?

RobbyG

New member
I know everybody is going to say yes it's absolutely needed. Let me explain and you be the judge.

I have noticed that my ORP probe almost never needs calibration. If I soak it for 45 minutes in Kent probe cleaner and then calibrate it in 240mv fluid it will usually read 237 or 239, just about exactly right. My Salinity probe is just about the same, it is off by only a fraction after I clean it.

So based on that, I decided on my last cleaning routine (3 week intervals) to soak my Pinpoint pH probe in the kent cleaner for 40 Minutes, much longer than the 10 minutes that I normally do. This time when I calibrated it with the Pinpoint solution the 10.00 fluid read exactly 10.00 and the 7.00 read 6.98
After seeing that I realized that the probe might not need calibration if I cleaned it properly.

My conclusion on ORP and Salinity probes is that they don't change because they don't have anything that could change. The only thing that effects there reading is the coatings that develop on their surface and once that's removed they return to the exact reading they had when they where clean. The thing is, I am not so sure about the pH probe since it depends on a liquid inside the probe. Does anybody know if that liquid's composition changes over time or does it stay the same and just run out over time?

Any thought s or idea's on the subject would be welcomed:)
 
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bertoni

Premium Member
My pH probe will drift out of calibration, even with cleaning. I'd recommend checking from time to time.
 

RobbyG

New member
Jon next time you clean your probe, see how much it drifted.
Mine always reads lower over time. The reading before cleaning was 8.06 after cleaning it was 8.24 and after calibration it was virtually the same 8.24

My
 

webbstock

New member
In lab, we use pretty expensive pH meters, and, in general, as long as the probe is stored properly and cleaned there is little drift.

I think the bigger problem is if the fluid in the probe becomes contaminated or leaks, then your readings will drift. My suggestion would be to at least check your control buffers to make sure that the meter is reading correctly. Remember that pH is a log scale, so a change from 7 to 8 is actually a 10-fold change.
 

Billybeau1

Premium Member
Robby, the real issue is longetivity of the probes we are speaking of.

Generally, ORP probes are only suppose to last about 18 months. I used 450mv calibration fluid on mine and for the first year, it was spot on for the first year. 6 months later now, my probe is 15mv off. This is with proper cleaning in muratic acid. At this point, I just compensate and adjust for the 15mv difference, but I know, at some point, I'm going to have to replace the probe.

These probes do not last forever.

pH is my next example. When I first bought my Pinpoint pH monitor, I would check calibration once every 6 weeks or so and it would be spot on. Then as the probe got older, it became increasingly difficult to zero the probe in between 7.00 and 11.00 pH. Back and forth, back and forth, you know how that goes.

At some point, this probe will to have to be replaced.

Just face the facts my friends. The bottom line is......... probes supplied with electronic monitoring devices will have to be replaced.

From my experience, the magic number looks like about 24 months.
 

Boomer

Bomb Technician (EOD)
Premium Member
From my experience, the magic number looks like about 24 months.

That is more like the max "wish number" Billy :D Many labs change probes 1 / yr and allot depends on what kind of probe it is and how it is treated.
 

RobbyG

New member
I agree the probes do drift over time but it seems like they are very steady for fairly long intervals. What I am saying in a nutshell, is it really necessary to recalibrate a pH probe every 2-3 weeks or can it be just cleaned and do the calibration every 3-4 months.

Does anybody think that the longer soak in (acid / Kent probe solution) is going to shorten the pH probes lifespan?

My probe is about 5 months old and so far from what I am seeing I could have calibrated it the first time and only cleaned it for the last 5 months and it still would have been reading accurately.
This is certainly true for ORP and Salinity, is it true for pH??
 

RobbyG

New member
<a href=showthread.php?s=&postid=9817159#post9817159 target=_blank>Originally posted</a> by Boomer
From my experience, the magic number looks like about 24 months.

That is more like the max "wish number" Billy :D Many labs change probes 1 / yr and allot depends on what kind of probe it is and how it is treated.

Same here, I get 1 year on pH probes then they start to become difficult to calibrate.
 

RobbyG

New member
<a href=showthread.php?s=&postid=9814331#post9814331 target=_blank>Originally posted</a> by webbstock
In lab, we use pretty expensive pH meters, and, in general, as long as the probe is stored properly and cleaned there is little drift.

I think the bigger problem is if the fluid in the probe becomes contaminated or leaks, then your readings will drift. My suggestion would be to at least check your control buffers to make sure that the meter is reading correctly. Remember that pH is a log scale, so a change from 7 to 8 is actually a 10-fold change.
Thanks, I think I will do that, I will just check it against the 7.00 every 3 weeks and see if it's still on target.
 

goreefer

New member
A question about cleaning,
Can you clean the probes in vinegar?
Or do I need a specific probe cleaning solution?
 

loudell

New member
The reason that probes like pH and ORP will "wear out" has to do with the fact that the internal reference fluid becomes more dilute as time goes on until it reaches a point where the internal fluid is so dilute that you can not calibrate your probes.
Prove it to yourself by comparing a new and very old probe. Check the viscosity of each by moving the internal air bubble.
BTW may peope actually do get 24-30 moths from a PINPOINT probe. I'll tell you how they do it but can anyone guess why??
 

Boomer

Bomb Technician (EOD)
Premium Member
I'll tell you how they do it but can anyone guess why??

Yours probes are made by Sensorex :D

It is the design of the ref junction for the most part.

I have a Horiba Cardy, 10 years old and still calibrates but is getting very drifty. An ISFET will last longer than anything.

Nice to see you Lou. So where is our commission for all the business we have given you ? Your are going to need a tanker truck of the 53mS before we get done with you :lol:
 

loudell

New member
Hi Boomer, A few things.
1-my probes have never been made by Sensorex.
2-the reference junction is not something within the hobbyist control so if you read my thread carefeully you would have known that it was not really a possible answer.
3-I would rather not sell any of the 53.0 fluid because it was really meant to support the electronic Salinity Monitor .

I'll give you the answer to the probe riddle tonight. That will be your commission.
 
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Boomer

Bomb Technician (EOD)
Premium Member
Ok

1. Maybe Broardley-James> You wouldn't tell us anyway but it would not be hard to figure out. Inexpensive probes are pretty much the same.

2.Ok, ture. By pre-soaking the probe in 2- 4M KCl after cleaning and before calibration extends probe life. Also letting it sit in each cal solution for a couple of minutes is better than a quick dip. Cleaning should actually be a rotaing cycle in .1 M NaOH and then HCL at least twice.

So increasing the life of a PinPoint is no different than most other probes, so there nothing special about the probe itself, as it is a user thing.

3. What does that have to do with anything :lol: A solution to calibrated a refract that works and woks accurately is a calibration solution. It makes no difference what its intended purpose was. That is like saying don't use baking soda in a aquarium to increase Alk because it was made for baking and not aquariums.
 
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loudell

New member
<a href=showthread.php?s=&postid=9824140#post9824140 target=_blank>Originally posted</a> by Boomer
Ok

1. Broardley-James

No Boomer. Not Broadley-James (or Broardley-James either) and I won't continue in the guessing game further. It's basically unique and I know you may have a hard time accepting that.

2.Ok, ture. By pre-soaking the probe in 2- 4M KCl after cleaning and before calibration extends probe life. Also letting it sit in each cal solution for a couple of minutes is better than a quick dip. Cleaning should actually be a rotaing cycle in .1 M NaOH and then HCL at least twice.

I don't know if this is true but I doubt it would extend the life 30% or more. Sounds like this will give you a faster response time but not extend probe life.

So increasing the life of a PinPoint is no different than most other probes, so there nothing special about the probe itself, as it is a user thing.

This is the first statement you got right but I already said that in my first reply.

3. What does that have to do with anything :lol: A solution to calibrated a refract that works and woks accurately is a calibration solution. It makes no difference what its intended purpose was. That is like saying don't use baking soda in a aquarium to increase Alk because it was made for baking and not aquariums.

The PINPOINT Fluid does work well on refractometers however it really was not priced for that purpose. There really is not a fair profit at the end of the day and it was intended to just support the PINPOINT Salinity Monitor.
For the owner of a refractometer after the original refractometer purchase then the purchase of PINPOINT Salinity Fluid it makes me wonder why someone would not spend the extra money and get the meter to begin with..
 

Boomer

Bomb Technician (EOD)
Premium Member
This is the first statement you got right


No, that would be 2 and 3. Your profit margin does not count. So you just got 2 out of 3 wrong.

1. I figured that.

2. Well, it is a common practice soaking in KCl to extend the life of the probe. Your 30 % is based on what ? And 30 % is better than 0 %. Some probes can also be recovered by soaking them in isopropyl alcohol for a few minutes.

3. Profit, you are selling tons of the stuff now since we started this. Because refracts are cheaper and serve the hobby well and not everyone wants or can afford a EC meter, although yours is the best bang for the buck. They have to buy or use some type of cal solution anyway. Refracts do not have to be replaced like EC probes either which can go bad to include the meter.

I'll give you the answer to the probe riddle tonight

What riddle ? What is the purpose of tonight. Maybe some reading this my want to know now. I didn't know this was a game.:rollface:
 

Billybeau1

Premium Member
I'm sure if you raised the price of your 53ms to achieve a fair profit, aquarists would still buy it. We want precision from our testing instruments and thats what your product provides us. I don't have to tell you how many refractometers are sold annually.

It is refreshing to see something actually perform well in the hobby.

BTW - I tested the 53ms fluid with my lab grade floating hydrometer and it was 1.0265 on the button.

Boomer - I like games :rollface: :rollface: :rollface:
 
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loudell

New member
The placement (location) of a pH probe will have a significant impact on the ultimate life of that probe. Keep in mind that the reason a probe wears out is the dilution over time of the internal reference fluid. The more and faster the flow past the probe tip will drain the electrolyte accordingly. The overflow will probably drain it the quickest and the corner of the sump will usually be the slowest drain.
Obviously there will be a time lag associated with the pH change registered in the corner of the sump versus another location but the difference may be literally seconds.
I hope this was helpful and I'm sorry if it turned into a dialog at times. This forum has always been "cutting edge" to exchange useful information and it's definately useful to all sides of the industry... :)
 
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