Conductivity Calibration Solution

[masaccio]

Looking for fresh calibration solution for my old TDS meter. Found this Ex-Tech stuff on Amazon. The new stuff is 1413uS and my original stuff was 1410uS. Labelled "For KCI standardized meters". It's expensive though ($28 for a couple of pints) and I believe this stuff usually has only a few months shelf life. Should I go for this? Suggestions? Thanks!

 

[masaccio]

Oh, I think I may be getting this now. The calibration solution doesn't have to be potassium chloride. I found a small bottle of NaCl at 1000 ppm. Why wouldn't that work on my meter. A little worried because I have run across the phrase "KCI-based meters". But since the meter doesn't just measure KCI, and it can be calibrated to 1000ppm, why would there be a problem? Thanks for any input. I'm doing my own digging, but not a scientist, or even a tech.

 

[Ozpaph]

I cant see why it would matter as both Na and K are monovalent

 

[masaccio]

I cant see why it would matter as both Na and K are monovalent

Thanks!

 

[Ray]

The trouble is that you're looking for a "TDS calibration solution", not conductivity, and the electrical conductivity of KCl and NaCl solutions at the same concentration are not the same.

You'd be much better off buying some distilled water and using it for your "zero" concentration, then mixing a fertilizer in it at a known true concentration, and measuring what your meter tells you.

I documented how I did that many moons ago.

 

[CarlG]

Are we talking concentration on a weight basis, or molar/molal/specific activity basis?

 

[Ray]

Are we talking concentration on a weight basis, or molar/molal/specific activity basis?

I would think we're sticking to a weight basis, as that's what ppm is.

 

[CarlG]

Well, that's a good point.

 

[masaccio]

The trouble is that you're looking for a "TDS calibration solution", not conductivity, and the electrical conductivity of KCl and NaCl solutions at the same concentration are not the same.

You'd be much better off buying some distilled water and using it for your "zero" concentration, then mixing a fertilizer in it at a known true concentration, and measuring what your meter tells you.

I documented how I did that many moons ago.

Thank you, Ray. Sounds like a plan.

 

[Ozpaph]

thanks Ray for the clarification