Originally posted by robbie carrobie
Great ones! are there any chemists among you who could advise me on a viable way to measure Ph that does not cost a fortune. Basically I have tried everything and nothing satisfies. I have a cheap PH pen which after calibration worked once then failed. I bought a Ph meter designed for use in soil hoping that it would prove trustworthy in an aqueou ...[text shortened]... a chemical method more accurate than these other methods? Basically I need accuracy to a tenth.
Here is the trick with Ph meters: you need to clean them out with Di water after every use and keep the sensor tip in Di water to keep it at a 7 or so Ph #, neutral, in other words so it can sense the changes from 7, up to 14 or down to 1 whatever.
I don't think they make much of a point of that for those instruments but that is the skinny.
We found that out the hard way, the dang sensors cost's a couple hundred bucks and of course they want to continue selling sensor tips.
There are also vials of Ph #'s you can get for calibration, say a Ph vial marked 3 and that is the cal level for that Ph #, but they have them from 2 or 3 up to 14 or so and as long as you have a sensor tip stored in Di water then stick it in the cal liquid, you can see how well the instrument performs before you make measurements.
I think you know what Di water is, "De-ionized'' which means the resistance is up around 18 megs/square cm which is as good as water gets.
Ordinary tap water clocks in at 3 or so Kilohms because of the contaminants.
Distilled water clocks in about 100,000 ohms or so, better but not up to Di water standards.
For our work we have to use Di water at a resistance level of at least 5 megohms or so, which means there are still contaminants but not enough to spoil our cleaning processes.
18 megs is much better.
We also use Di water as a cooling liquid against a high voltage, since you can run a meter or so of plastic tubing with Di water for cooling and it can hold off hundreds of thousands of volts, our ion implanters uses voltages in that range and we used to be able to cool them with liquid freon but no more, we have to use other high impedence liquids and Di water is one of them, another is mineral oil, which has its own problems, like flammability. You can't burn Di water🙂
Anyway, get a flask of Di water and a little glass, like a test tube or some such to keep the tip immersed. That way it won't dry out. Drying out kills Ph sensors, but you can't just store them in tap water, too contaminated.
If you can't get DI water, use distilled, better than nothing.
And get Ph cal liquids, say a 3 and a 10 or so, that will give you confidence the tip will do it's job.
Here is one site that has stuff like that, long URL though:
Looks like they have just 2 levels, 4 and 7.
This forum talks about how to make your own cal liquid, Potassium Choride and Di water, probably cheaper just to buy already made: