Fluoride measurement: ISE vs. IC

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 ...

.

Relevant Pages

  • Fluoride measurement: ISE vs. IC
    ... 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 ... The technical support from Thermo said the electrode ...
    (sci.chem)
  • Re: Fluoride measurement: ISE vs. IC
    ... in a defined bacterial medium with about 400 ppm of chloride and 1000 ... ppm of phosphates. ... The technical support from Thermo said the electrode ... system) is that the fluoride peak elutes close to the water peak. ...
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  • Fluoride measurement: ISE vs. IC
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