Dual-analyte spectroscopic sensing in sol-gel derived polyelectrolyte-silica composite thin films

Ferrozine (3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p'-disulfonic acid, monosodium salt hydrate), an iron indicator, and HTPS (8-hydroxyl-1,3,6-pyrenetrisulfonic acid, trisodium salt), a pH indicator, were immobilized in sol-gel derived PDMDAAC-SiO(2) (where PDMDAAC stands for poly(dimethyldiallylammonium chloride), composite thin films via ion-exchange. The two indicators were immobilized in two adjacent sections of the same PDMDAAC-SiO(2) film which was supported on a glass optical substrate. The spectroscopic response of the film to both Fe(2+) and H(+) in solutions was investigated by attenuated total reflection (ATR) spectrometry at two well-separated wavelengths, 562 nm for Fe(2+) and 460 nm for H(+). The Ferrozine/HPTS immobilized PDMDAAC-SiO(2) films had the following characteristics: linear range, 2.5x10(-6)-5.0x10(-5) M for Fe(2+), pH 4.1-6.8 for H(+); sensitivity, 2.2x10(4) DeltaA/M for Fe(2+), 0.583 DeltaA/pH for H(+).