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Solvent Vapour Detection with Cholesteric Liquid Crystals—Optical and Mass-Sensitive Evaluation of the Sensor Mechanism†
Department of Analytical Chemistry, University of Vienna, Waehringer Strasse 38, A-1090 Vienna, Austria
† Dedicated to Professor Rolf Saalfrank on the occasion of his 70th birthday.
* Author to whom correspondence should be addressed.
Received: 18 March 2010; in revised form: 4 May 2010 / Accepted: 6 May 2010 / Published: 12 May 2010
Abstract: Cholesteric liquid crystals (CLCs) are used as sensitive coatings for the detection of organic solvent vapours for both polar and non-polar substances. The incorporation of different analyte vapours in the CLC layers disturbs the pitch length which changes the optical properties, i.e., shifting the absorption band. The engulfing of CLCs around non-polar solvent vapours such as tetrahedrofuran (THF), chloroform and tetrachloroethylene is favoured in comparison to polar ones, i.e., methanol and ethanol. Increasing solvent vapour concentrations shift the absorbance maximumto smaller wavelengths, e.g., as observed for THF. Additionally, CLCs have been coated on acoustic devices such as the quartz crystal microbalance (QCM) to measure the frequency shift of analyte samples at similar concentration levels. The mass effect for tetrachloroethylene was about six times higher than chloroform. Thus, optical response can be correlated with intercalation in accordance to mass detection. The mechanical stability was gained by combining CLCs with imprinted polymers. Therefore, pre-concentration of solvent vapours was performed leading to an additional selectivity.
Keywords: cholesteric liquid crystals; organic solvent vapours; pitch; optical absorbance; QCM
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Mujahid, A.; Stathopulos, H.; Lieberzeit, P.A.; Dickert, F.L. Solvent Vapour Detection with Cholesteric Liquid Crystals—Optical and Mass-Sensitive Evaluation of the Sensor Mechanism. Sensors 2010, 10, 4887-4897.
Mujahid A, Stathopulos H, Lieberzeit PA, Dickert FL. Solvent Vapour Detection with Cholesteric Liquid Crystals—Optical and Mass-Sensitive Evaluation of the Sensor Mechanism. Sensors. 2010; 10(5):4887-4897.
Mujahid, Adnan; Stathopulos, Helen; Lieberzeit, Peter A.; Dickert, Franz L. 2010. "Solvent Vapour Detection with Cholesteric Liquid Crystals—Optical and Mass-Sensitive Evaluation of the Sensor Mechanism." Sensors 10, no. 5: 4887-4897.