Flow-through type fiber-optic silver ion selective optodes based on no
vel cyclic and noncyclic thia crown ether compounds and a Lipophilic a
nionic indicator dye have been developed. Pellicular octadecylsilica b
eads were coated with a lipophilic organic liquid containing the thia
ether compound as the silver ion selective ionophore and LAD-3 as the
color changeable indicator dye, The optode system was constructed by p
acking these color changeable ion sensing beads ina now-through optica
l cell (cell volume, 7 mu L) having a quartz window attached directly
to the distal end of a bifurcated optical fiber. The optode based on a
lipophilic thia crown ether that has two sulfur atoms (tetradecyl-14-
dithiacrown-4) exhibited the most sensitive response to silver ion of
all the optodes investigated. This optode could detect silver ion in c
oncentrations ranging from 10(-6) to 10(-2) M at pH 7.0 with 0.05 M Tr
is-H2SO4 buffer as the flowing solution by measuring the absorbance ch
ange in the sensing beads at 516 mm. This optode showed a higher selec
tive response to Ag+ without any interference from other transition me
tal ions, except for Hg2+, up to 10(-3) M, as well as alkali metal and
alkaline earth metal ions up to 1 M. Optodes employing highly lipophi
lic ionophores showed good reproducible response to Ag+ for at least 2
weeks.