Probing technique - pH meters

Being the delicate probe a pH probe is, I prefer not to stir with it. I just swish my liquid in my beaker and gently lower the probe into it.

Regards, Gene

Thank you Gene. I am trying to figure out why I got 3 different readings in a row. Tomato sauce, actually. I calibrated, tested. Recalibrated, tested. Recalibrated, tested. Even if my pH 4 and pH 7 fluids were old, I'd expect repeatability. Two place resolution, +/- .04 accuracy. I got 4.41, 4.16, and

Personally, I'm from the "stir gently, wait, stir again and wait until the reading stabilizes" school. I do this when running standards too. It takes time for the reading to settle to a final value. Also, the time required to stabilize will lengthen with age of the probe. Supposedly, contact lens enzyme cleaner helps restore/clean dirty probes.

BTW, I had trouble with flaky connections between the probe and body of my Hanna Piccolo, so I soldered jumper wires between the sets of contacts. That did the trick.

Tom S

Hmmm.... could the solids in the tomato sauce have gummed up the pH sensor electrode so that it is not being flushed adequately between readings? I wouldn't expect recalibration to get you back to the start if there's a barrier to solution transport across a tomato solids layer. You have an interesting dilemma. Any gurus out there to help? Gene

I have only used it once, which was last season. I stored the probe in the little tip it came in, submersed in whatever solution that is (KNO3?). The instructions say to soak it in 7 pH calibration fluid for several minutes to freshen it up. I didn't do that but will next time. I did use distilled water for my probe rinsing. In truth, I must admit that the calibration solutions I used this year, were left over from LAST year, stored in little Mason jars. I have "fresh" packets of 4.0 and 7.0 from last year. I'll at least break those out and try again. Ken

That sounds pretty old, mine go bad in 2 to 3 months. If you see mold or 'floatsies', they are bad.

Maybe see if you can find a supplier of Hydrion capules. They come in a pak of 10 of 4, 7, and 10. All you do is add them to 100 ml of distilled water and add 3 drops of preservative. Mine last 2 months, so that's over a years worth for around $20.

I do not use distilled to rinse, I use tap water. Either deionized or distilled is hard on pH probes, I can't remember just now.

Joe

In truth, I must admit that the calibration

I get a special cleaning solution that you can soak you probe in. I think it is very acidic. It make a real difference. I suggest you look into getting some. Also, I forgot to ask if you were storing it in storage soluton. This too can make a difference.

Ray

Ray - What is the solution and where do you get it? Bill Frazier Olathe, Kansas USA

I've heard people use contact lense cleaning solution with good results.

Pp