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Flawed PH meter readings?
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I hope soon to have more answers then questions.I have been doing a lot of work with making bar soap using KOH reacted bio glycerin.I will soon have a lot to offer from my work.I have been using a "HM PH-200 meter"since the start along with PH strips and have had no problems.I have formulated recipes that are reliable enough that recently I have only been using the meter at the end and PH has been perfect every time.Things have changed.Suddenly PH is 10.8 and boric acid was not making a difference.I re calibrated the meter many times ,checked my boric acid ,checked the meter.After much fooling around I went back to strip testing and found that the problem appears to be solely with the meter.In 7 buffer solution or distilled water the meter will read 7 but in the soapy water it reads 10.8 or so. PH strips will read a solid 8..My recipe has proven to result in a high 8 in the past so I am choosing to believe the strips.The meter was giving equal results as the strips in the past.What could be causing this problem now?
 
Location: la gloria | Registered: October 02, 2010Reply With QuoteReport This Post
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I too got some real "interesting" readings the other day with my pH meter while trying to determine a sap value of my glycerin. Never having done it before(or hot process soap), I stopped when the goo got thin(I wasn't expecting it - but I now know it's supposed to happen.) figuring that I messed up. I couldn't make heads or tails out of the readings - the pH of the SAP solution was the same as the soap @ 10.6. I noticed I had a little bit of a bubble in the glass - I guess I hadn't soaked it long enough(It's a brand new meter - single junction). Not sure if I was taking the pH of the soap right either - I was just sticking the meter into it. I know pH meters(especially single junctions) like more fluid materials than soap to read, but other than doing as I did I'm not sure of the way to get the right reading other than making a slurry. Making a slurry has its own challenges - I'm not sure just how to make one in small quantities accurately and quickly for a pH reading.

Upon further reading, it appears that there's an electrolite in the glass bulb that's supposed to weap through the glass and that it gets depleted over time. It's recommended to store the meter's buld moist/wet in storage solution(whatever that is).
 
Location: Santa Cruz, Ca | Registered: July 29, 2006Reply With QuoteReport This Post
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My meter worked fine in the beginning and it is only a couple months old.I would just take a little soap and dissolve it in some water and test.I have stored it with the cap on and used the 7 buffer solution in the cap to keep it wet.I did fall asleep a couple of times with the meter in distilled water.It was not left in there for more then 8 hours.It seemed to work after those mishaps.It still reads the buffer just fine.Maybe keeping it soaked in that is the problem.I really wish I knew a way to get it to work again.It made things way easier!
 
Location: la gloria | Registered: October 02, 2010Reply With QuoteReport This Post
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Bernhardt is right. pH probes contain an electrolyte much like car batteries. KCl, is used as far as I know. Although that fact that your probe is reading too high means the membrane is clogged more often than not... try soaking it in a weak solution of HCl or boric acid that sometimes helps. If that doesn't work try looking up what electrolyte it uses and changes that. We typically changed ours every 6 months regardless but I don't think that's really necessary to be honest
 
Registered: February 25, 2010Reply With QuoteReport This Post
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