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

Cholesteric liquid crystals are suitable as sensitive materials for th e detection of solvent vapours, such as aromatic and halogenated hydro carbons. The optical properties of these materials are determined by t heir molecular short range order, given by the so-called pitch which i s influenced by analyte incorporation. Thus, the wavelength of the abs orbance band is shifted and the sensor effects are followed in the vis ible range at a defined wavelength on the flank of the band. Even a va riety of aromatic or halogenated solvents, e.g. tetrachloroethylene, c an be detected in the ppm-range. By using the whole spectral informati on combined with partial least squares analysis a separation of solven t effects from that of the disturbing temperature is achieved. Further more, these spectral data allow the optimization of the detection of h alogenated hydrocarbons whereas the cross sensitivity to other analyte s can be diminished.