CHOLESTERIC LIQUID-CRYSTALS FOR SOLVENT VAPOR DETECTION - ELIMINATION OF CROSS-SENSITIVITY BY BAND SHAPE-ANALYSIS AND PATTERN-RECOGNITION

Cholesteric liquid crystals are suitable as sensitive materials for the detection of solvent vapours, such as aromatic and halogenated hydrocarbons. The optical properties of these materials are determined by their molecular short range order, given by the so-called pitch which is influenced by analyte incorporation. Thus, the wavelength of the absorbance band is shifted and the sensor effects are followed in the visible range at a defined wavelength on the flank of the band. Even a variety of aromatic or halogenated solvents, e.g. tetrachloroethylene, can be detected in the ppm-range. By using the whole spectral information combined with partial least squares analysis a separation of solvent effects from that of the disturbing temperature is achieved. Furthermore, these spectral data allow the optimization of the detection of halogenated hydrocarbons whereas the cross sensitivity to other analytes can be diminished.