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, 2.5×10 −6–5.0×10 −5 M for Fe 2+, pH 4.1–6.8 for H +; sensitivity, 2.2×10 4 Δ A/M for Fe 2+, 0.583 Δ A/pH for H +.