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Re: Ion Meters and testing

On Mon, 21 May 2001, Bob Olesen wrote:

< to Tom Barr>
> Speaking of quick tests - could you elaborate a bit on those "ion meters" you
> spoke of recently?  If I remember, I think you said they enable one to
> quickly and accurately test for N, K, P, and trace etc.


The ion-specific probes are conceptually similar to pH probes.  They don't
have anything to do with conductivity measurements.  The probe produces a
response that is in proportion to the concentration of a specific ion.
You can get probes for NO3-, for instance, but not for N, because N isn't
a specific ion.

To use the ion-sensitive probes you would need a meter to plug the probe
into.  One meter can handle several different kinds of probes, but the
meters themselves cost anywhere from a few hundred dollars to a few
thousand dollars.  Then you would need the probes themselves.  One for
each ion you want to measure and several hundred dollars each.  Finally,
you would need all the standards to calibrate the probes and the meter.
Frequent calibration is normal, but the probes don't necessary last as
long as you might think.

So, while ion-sensitive probes are a pretty cool technology they are *not*
very affordable.  A new catalog has complete systems starting at $3700.
It sounds like the sort of thing that George Booth might have.  On the
bright side, the cost of an average setup has probably dropped by about
50% in the last few years, and they definitely make them rugged enough for
field work.

One supplier told me that if we were interested enough that they could
build a probe to read just about anything we wanted.  Warranty extra.

If you're really into trying one, you can probably rent a setup from a
local environmental equipment supplier (someone like Enviracare or Rocky
Mountain Geotech).

Roger Miller