I used several ion selective electrodes (e.g. Pb2+, K+, F- and Ba2+) before. If you use a different type ion selective electrode (different to the tested ion species), you'd better try to apply an indirect way. Say, add something (certain amount, chemical like inorganic salt) to react with the fluoride ion to give precipitates (or other solid like material that can not dissociate into ions any more), then use your iron selective electrode to detect the excessive iron ions. Base on the standard curve, you can figure out the amount/concentration of the fluoride ions. The values will not be very accurate, but will be useful for some purposes. Recommend to use another technique to do that, say ion chromatography, etc

Dear Mr Nath, I didn't understand your question. Do you use iron selective electrode for determining of fluoride? or Do you want to determine fluoride using Ion Selective Electrode (ISE). There is a ISE-Fluoride based on lanthanium crystal doped with europium. This electrode measures fluoride in the range between 10-6 up to 10-1 mol L-1. This electrode is very much selective for fluoride when comparing with others anions that can be interferents. it is necessary to use a TISAB (Total Ionic Strength Adjustment Buffer). There is also many manufactures of ISE-F. See the links:

http://en.wikipedia.org/wiki/Total_ionic_strength_adjustment_buffer;

http://www.nico2000.net/analytical/fluoride.htm;

http://www.nico2000.net/datasheets/electrodes.html.

Normally, ISE-F is not a combined electrode, therefore is necessary to use a reference electrode together. I hope this answer helps you.

Thanks for the kind reply> please tell me if there is any chromatographic methods to determine it say using GC-MS...

Dear Mr Nath, maybe be possible to use ion-exchanger chromatography (http://en.wikipedia.org/wiki/Ion_chromatography) for determining of fluoride . I think that is not possible by gaseous chromatography (GC), once fluoride salt presents high boiling point. In case of ion-exchanger chromatography, the mobile phase is liquid (buffered aqueous solution). On the other hand, to use chromatography for determining fluoride ions is very more expensive than ion selective electrode for fluoride. ISE-F is very selective and just undergoes interference of hydroxil ions. Kind regards.

Thank you Julio.....