Development of a flow manifold for Fe(III) ion determination with a fluoride ion-selective electrode.

Continuous-flow (CF) and flow-injection (FI) analysis using the fluoride ion-selective electrode (FISE) as detector have been investigated. The measurements were performed in a home-made cell under appropriate flow conditions (2.86 or 3.45mlmin(-1), 0.2ml samples, 10(-6)M sodium fluoride). The calibration graph was obtained by plotting the signal height versus concentration of iron in the range of Fe(III) concentration from 10(-5) to 10(-1)M in acetate buffer (pH 2.8 or 3.4). In all described procedures, the range of linear response extends to the Fe(III) concentration from 1x10(-3) to 1x10(-1)M, with detection limit 9x10(-5)M. The effect of double-line, two-line flow manifold and CF was investigated and discussed.

Fluoride electrode with LaF(3)-membrane and simple disjoining solid-state internal contact.

Fluoride-selective electrode with LaF(3)-membrane and stainless steel internal contact has been prepared. The electrode has been tested in F(-) concentration range 10(-2)-10(-6) M and the results compared with those of commercial electrode and electrode with laboratory renewed internal electrolytic contact. The properties of simple disjoining solid-state contact have been investigated by means of electrochemical impedance spectroscopy (EIS). The impedance spectra show two time constants, which suggest that, at lower frequencies, proceed some Faradic reaction which probably stabilizes the potential between LaF(3)-membrane and stainless steel disk.