pH-meter questions

Mick Fagan · Apr 8, 2010

Ralph, I currently have the Hanna pHep 3 pH meter. This is my third Hanna pH meter.

The first two were the first model they released, it died when I slipped it into some C41 solution.

The second just wore out, it had bad battery contacts due to the presence of heated C41 chemistry adding moisture to the unit.

The third is my current one and it's close to falling apart. It's waterproof, yep, slipped it into a solution a few years ago, rinsed it under the tap and continued using it.

Today the battery cover, which uses a coin is starting to break up, plus the battery contacts are a bit hit and miss these days.

The beauty of these little wonders is that they have automatic temperature compensation from 0º to 50ºC.

The instructions for a similar meter from Hanna is here:- http://www.hannainst.com/manuals/manHI_96108.pdf

Initially (about 20 years ago) I tested my first meter constantly at my work, against a (calibrated four times daily) pH meter. It was amazingly close, not the same, but for the cost and simple manner of use, good enough for me.

I would suggest you purchase buffer solutions pre-mixed from a local source, 500ml bottles would be my suggestion. I myself have 4, 7 and 10 and with these I was able to check and adjust all C41 solutions as I mixed from stock chemicals, and have results as consistent and as good as, the professional lab I worked in.

Regarding storage and with the Hanna meters, which are probably extremely similar to your yellow one, they suggest you store the electrode with a few drops of pH 7 buffer solution in the cap.

From memory they specifically suggest not to store in distilled or de-ionised water.

Mick.

OldBikerPete · Apr 8, 2010

I, too have a Hanna pH meter.
Before I retired I had been using pH meters in my career as an analytical chemist since the 1960's when they were steam driven!! Over this time I have found that the best storage medium for the electrodes is to immerse them in a saturated solution of KCl which is buffered to pH 7.0. (The calomel half of the electrode system contains a saturated solution of KCl behind a porous glass membrane. If you store the electrodes in water then this electrode becomes diluted over time, if you store it dry then that electode will slowly dry out - but will work properly until it does).

RalphLambrecht · Apr 8, 2010

I believe the Hanna pH meter is a good proposal. They are at pHep 5 at the moment, but the only difference ti the pHep 4 is two-digit read out. I'm fine with a 0.1 read out, and will go for the pHep 4. I will store it in 3 M KCl solution and see where that takes me.

Thanks for all the good advise and the Hanna recommendation!

Nicholas Lindan · Apr 8, 2010

I notice many pH meters can also take ORP (oxidation/reduction potential) electrodes.

Would an ORP reading have any usefulness in evaluating developer action? Specifically, would it detect failed (and failing) XTOL?

Kirk Keyes · Apr 8, 2010

fotch said:
Kirk, how would the "Hanna pHep 4" be?

Hanna makes good equipment, and are commonly used in industry.

And "stick" type meters are convienent to use - they are small and portable.

Stick-type meters do have the issue of non-replaceable electrodes, but the cost is often what one would pay for a new pH electrode, so it could be a wash cost-wise.

My background is from chemistry labs and having used pH meters for over 20 years, I prefer lab type meters with replaceable electrodes.

That said, I've used PE's Hanna meter and it worked just fine for what we were doing - adjusting the pH of an emulsion that I was helping PE make.

RalphLambrecht · Apr 8, 2010

Kirk Keyes said:
Hanna makes good equipment, and are commonly used in industry.

And "stick" type meters are convienent to use - they are small and portable.

Stick-type meters do have the issue of non-replaceable electrodes, but the cost is often what one would pay for a new pH electrode, so it could be a wash cost-wise.

My background is from chemistry labs and having used pH meters for over 20 years, I prefer lab type meters with replaceable electrodes.

That said, I've used PE's Hanna meter and it worked just fine for what we were doing - adjusting the pH of an emulsion that I was helping PE make.

Kirk

Good news! The Hanna pHep 4&5 meter electrodes are replaceable. The replacement electrode costs half the meter's original price, but they are replaceable.

Kirk Keyes · Apr 8, 2010

Nicholas Lindan said:
I notice many pH meters can also take ORP (oxidation/reduction potential) electrodes.

Would an ORP reading have any usefulness in evaluating developer action? Specifically, would it detect failed (and failing) XTOL?

Nicholas - there's really nothing special about lab-type pH meters when comparing them to a high quality volt meter. The important thing about pH meters is they need to have high input impedance so they don't affect the potential that the electrode is generating.

So if you have a good volt meter, and I trust you do, then you could use one with an ORP electrode. The electrode will probably not have a connector on the end of the cable that will mate nicely with a voltmeter, but then adaptors can always be used.

As far as your second question, I'm not sure it would work. Certainly you can make ORP measurements of developer, and certainly the ORP value will change as the developer ages and dies. But I guess is the question is does the developer die at a certain point on the ORP curve.

I don't think it's as simple as when the solution changes from reducing to oxidizing and then the developer is dead. I guess it would be bad long before that point. The excess of sulfite in XTOL will probably ensure that. But it could certainly be used as an indicator.

But then a clip test of exposed film can tell us that in about 5 minutes, and I think you would spend much more time getting your ORP electrode functioning and calibrated than the clip test takes.

Kirk Keyes · Apr 8, 2010

RalphLambrecht said:
Kirk

Good news! The Hanna pHep 4&5 meter electrodes are replaceable. The replacement electrode costs half the meter's original price, but they are replaceable.

That's good. And as long as it's accurate enough for your applications, then that would be a good, inexpensive choice.

Did I mention that lab-type pH meters can be used for making t-grain and high-speed silver gelatin emulsions??? You can make a silver ion specific electrode (I've done that - a couple times now) and buy (or probably make, but I haven't made one yet) a Ag|AgCl reference electrode and you are on your way to making fancy silver emulsions.

Murray Kelly · Apr 8, 2010

I was Googling Cream of tartar Potassium Bitartarate - and noted it is sparingly soluble in water and a saturated solution has a pH of 3.557. Pretty good for a standard at one end of the scale. I usually go for a M/10 solution of borax for the other end and set at just under 9.2. My homebrew recipies are more accurate than my guestimated exposures!
Murray

Kirk Keyes · Apr 8, 2010

Also, lab type meters usually let you calibrate for 3 points, and over a wider range then stick meters, and they also are programmable for the calibration - much easier to calibrate then using a little screw driver. Mostly it speeds up thier use.

RalphLambrecht · Apr 8, 2010

Kirk Keyes said:
Also, lab type meters usually let you calibrate for 3 points, and over a wider range then stick meters, and they also are programmable for the calibration - much easier to calibrate then using a little screw driver. Mostly it speeds up thier use.

Now I understand what Hanna meant when they say: 'as long as the calibration solution is within 0.04 pH, the meter will accept it and automatically calibrate to that solution'.

RalphLambrecht · Apr 8, 2010

Murray Kelly said:
I was Googling Cream of tartar Potassium Bitartarate - and noted it is sparingly soluble in water and a saturated solution has a pH of 3.557. Pretty good for a standard at one end of the scale. I usually go for a M/10 solution of borax for the other end and set at just under 9.2. My homebrew recipies are more accurate than my guestimated exposures!
Murray

Can you come up with something simple like that around a pH of 7.0?

Photo Engineer · Apr 8, 2010

Remember that when you replace a Hanna glass electrode, you must use their replacement tool in order to prevent injury to the electrode or to the meter itself. If you do not replace them correctly, a leak can develop around the seal of the electrode to the body.

PE

RalphLambrecht · Apr 8, 2010

Photo Engineer said:
Remember that when you replace a Hanna glass electrode, you must use their replacement tool in order to prevent injury to the electrode or to the meter itself. If you do not replace them correctly, a leak can develop around the seal of the electrode to the body.

PE

I conclude from this, it's not a bright idea to store the electrode in the storage solution and insert it every time you want to use the meter?

AgX · Apr 8, 2010

For storing an electrode in storing solution you do not have to take it off the meter.

Photo Engineer · Apr 8, 2010

Keep it on the meter to avoid wear and tear and outright damage to the meter or the electrode.

PE

Kirk Keyes · Apr 8, 2010

More strongly worded - do not take the electrode off the meter until you are ready to replace it with a new electrode.

RalphLambrecht · Apr 9, 2010

Got it guys. It stays on! Storage solution is ordered and on it's way.

Thanks for all the help.

Kirk Keyes · Apr 9, 2010

PE - does your Hanna meter have the junction that is a strip that can be pulled out, the external portion removed, and then it extends the electrode life? I see some of the Hanna meters have this feature.

Ralph, if yours has that feature, when the electrode gets slow to calibrate and the readings drift, you want to try refreshing the junction before replacing the entire electrode.

(The junction is a plug or fiber strip that electrodes use to let some liquid flow in and out of the electrode so that the internal reference electrode (which your has) can complete the circuit with the glass electrode.)

Kirk Keyes · Apr 9, 2010

Ralph - Ryuji Suzuki has a nice page on his site that discusses pH and photography that you may find interesting.
Dead Link Removed

Note that he points out the pH 10 buffers do not last as long as buffers with lower values of pH. This will be important to remember for photographic work since a pH 10 is going to be your regular pH cal point.

Also, he mentions the use of a calibration check standard. If you calibrate with 7 and 10, you want to use a pH 8 or 9 to check the linearity of your calibration.

Photo Engineer · Apr 9, 2010

Mine does not appear to have that sort of junction as far as I can determine. It is not mentioned in the instructions. The instructions say to replace the glass electrode when readings or calibration become inaccurate or slow.

PE

pH-meter questions

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