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8 May 1995 Modeling and analysis of fiber optic pH sensors: effect of the ionic strength
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Fiber optic-based pH sensors have many advantages over the traditional pH electrodes. They are robust, self-calibrating and show negligible drift. In addition, they are capable of detecting pH changes within 0.001 pH units. These features make fiber optic pH sensor technology particularly attractive for biomedical and on-line process applications. Typically, pH sensors consist of an indicator dye immobilized in a polymer matrix. The pH of the solution is related to the relative fraction of the protonated and dissociated species of the dye, whose absorption spectrum changes according to the pH of the surroundings. The response of the pH sensor is determined by the dissociation equilibrium of the immobilized dye, its interaction with the polymer matrix and the ionic strength of the medium. In order to have meaningful pH measurements it is important to understand the sensing mechanism and the resulting absorption spectra. In this paper a model is reported that takes into consideration the chemical reaction and the osmotic and electrochemical effects resulting from the dye-membrane-ionic strength interactions. Ionic strength effects are quantified through the pKa of the immobilized dye and it is demonstrated that highly reliable quantitative pH measurements, in the range required for blood pH analysis, are feasible.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sylvia H. Chang, S. L. Druen, and Luis H. Garcia-Rubio "Modeling and analysis of fiber optic pH sensors: effect of the ionic strength", Proc. SPIE 2388, Advances in Fluorescence Sensing Technology II, (8 May 1995);

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