Characterization of cyclodextrin modified infrared chemical sensors. Part II. Selective and quantitative determination of aromatic acids

In this paper, the selectivity and sensitivity of cyclodextrin (CD) modified infrared (IR) chemical sensor in detection of aromatic acids in aqueous solutions were reported. To eliminate the interference from water, the technique of attenuated total reflection was employed. By surface treated with CD molecules on the internal reflection elements, the sensors were selective in sensing of aromatic acids compared to aromatic compounds with other functional groups. To facilitate the use of this method for the quantitative analyses of aromatic acids in aqueous solutions, analytical functions were also developed in this work and a linear relationship between analytical responses and concentrations of analytes can be obtained. To optimize the analytical conditions, the factors that influence the IR spectroscopic signals were examined. These factors included response time, CD loadings of the sensors, pH effect on response, regeneration efficiency and stability of sensors. Under the optimal conditions, the detection limits for aromatic acids at a detection time of 2 min can be <100 μg/L. Meanwhile, the dynamic linear range for detection was only ca. two orders of magnitude if direct IR signals were used. Using the analytical function developed in this work, the linearity can be extended up to a concentration of 100 mg/L.