Polymer-Coated Cylindrical Waveguide Absorption Sensor for High Acidities

W. Patrick Carey, Michael D. DeGrandpre, Betty S. Jorgensen

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38 Scopus citations


The development of a chemical sensing scheme for the detection and quantitation of greater than 1 M concentration of acids, particularly nitric acid, is presented with the overall goal of using this chemistry to create optical sensors. The detection chemistry is based on the physical entrapment of Hammett indicators in a polymer blend of polybenzimidazole and polyimlde, which is silane-coupled to optical elements. The polymer coating protects the optical element from chemical attack, and Its hydrophilic nature and low porosity make the sensor more selective. By use of the indicator chromazurol-S, nitric and hydrochloric acid concentrations ranging from 2 to 10 M can be measured with a precision of 0.05 M. Indicators that cover a range of 0.5-10.0 M acid concentrations have also been investigated. Cylindrical waveguide sensors, using both a fiber optic and a sapphire rod with the immobilized polymer chemistry, were constructed based on the absorption of light by the acid Indicator, chromazurol-S. Because of the difference in the refractive index of the optical elements and the polymer material, separate detection techniques for the two sensors are presented. The fiber-optic sensor uses an absorption measurement of a thin film, and for the sapphire rod, an evanescent field absorption process occurs.

Original languageEnglish
Pages (from-to)1674-1678
Number of pages5
JournalAnalytical Chemistry
Issue number15
StatePublished - Aug 1989


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