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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.chem,sci.electronics
Subject: Re: Ion concentration measurement
Summary: Use of ion-selective electrodes
Message-ID: <3933@kitty.UUCP>
Date: 11 Aug 90 03:46:24 GMT
References: <32660@cup.portal.com>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 34

In article <32660@cup.portal.com>, dbell@cup.portal.com (David J Bell) writes:
> I'm looking for an inexpensive method of electronically measuring
> the concentration of copper ion in a water solution. I don't need
> great accuracy, even +/- 5 or 10% will be adequate. The level I'm
> reading will be on the order of 2 ppm, in the presence of a bunch
> of other "junk". I'd expect to get a low-level voltage or current
> which I could amplify and read with an A/D and microprocessor for
> a simple process control application. Long term stability of maybe
> a few percent and low cost are prime factors, with ruggedness not
> far behind...

	You can measure copper (more specifically cupric) ion concentration
using an specific ion electrode, available from Beckman, Corning, Orion, etc.
There is, however, a problem of interference in the presence of mercury,
silver, chloride and certain other ions.

	You will need a high input impedance electrometer circuit, as is
used for pH measurement.  With some care, such a circuit is not difficult
to build for measurements which do not require great accuracy.  Various
application notes from vendors such as Analog Devices, Burr-Brown, etc.
should give you example circuits.

	You won't like the price of the specific ion electrode, however.
You're probably talking about $ 200.00, minumum.

	There are other methods of measuring specific ion activity, such
as voltammetry, polarography, etc., but automatic interpretation of such
measurements would require a microprocessor and a potential control
device (potentiostat) under program control.  Simply stated, you probably
don't even want to know about these options due to their complexity.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231   {boulder, rutgers, watmath}!ub!kitty!larry
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