Sol-gel-based optical sensor for the detection of aqueous amines

We present an optical sensor for the detection of aqueous amines obtained by incorporating chromoionophore XV (ETH^T 4001) into sol-gel thin films. Acid- and base-catalyzed sol-gel processes were studied to prepare stable ormosil layers using various amounts of organically modified sol-gel precursor such as methyltriethoxysilane (MTriEOS). The sensor layers were coated with a protective layer of microporous white polytetrafluoroethylene (PTFE) in order to prevent interference from ions and ambient light. The measurements were carried out in a flow-through cell in the reflection mode. Acid-catalyzed ormosil layers (pH 1) based on the copolymerization of tetraethoxysilane (TEOS) and MTriEOS did not show any change in signal upon exposure to aqueous amine solutions, while base-catalyzed sensor layers (pH 3 and 13) showed significant changes in signal. The response time (t ₁₀₀) for the base-catalyzed sensor layer L3 (pH 13) upon exposure to different solutions containing 0–608 mmol L⁻¹ aqueous propylamine was 20–30 s, the regeneration time was 70 s and the detection limit was 0.1 mmol L⁻¹. The sensor response was reproducible and reversible. The porous ormosil layers permit dry sensor storage conditions.