Fluoride measurement: ISE vs. IC

liujx7@yahoo.com · science forum beginner Joined: 21 Jul 2006 Posts: 4

I am trying to measure low-level of fluoride (hopefully below 0.01 ppm)
in a defined bacterial medium with about 400 ppm of chloride and 1000
ppm of phosphates. I would like to get some opinions about which method
is better. So far I didn't have success with either of the method.

My ISE (IonPlus from Thermo) was about two years old, but it was only
used it for a week last year. It was stored dry as suggested in the
manual, but there was a little crystallization probably because the
filling solution wasn't completely rinsed out last time. The reading
slowly drifted and I can't get a stable reading after waiting for a
couple of hours. The technical support from Thermo said the electrode
should be good for a year and beyond that it is hard to say. I guess
the electrode is just too old. I don't have good luck with Thermo
electrodes. Does anyone know about the quality of Metrohm electrodes?

I also tried IC with IonPac AS11-HC column, but I only got detection
limit about 0.2 ppm. The IC system is a three-year old Dionex system,
and has been maintained well. The analytical column is about 2 years
old, and I don't know how heavily it has been used. The chloride and
fluoride peak are well separated, so I don't think high level of
chloride was a problem. I wonder what kind of detection limit you
usually get with IC?

Any suggestion or experience is highly appreciated! Thank you.

~ Fluoride means frustration ...

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