Odour perception in humans can sometimes discriminate different enantiomers of a chiral compound, such as limonene. Chiral discrimination represents one of the greatest challenges in attempts to devise selective and sensitive gas sensors. The importance of such discrimination for pharmacology is dear, as the physiological effect of enantiomers of drugs and other biologically active molecules may differ significantly. Here we describe two different sensor systems that are capable of recognizing different enantiomers and of qualitatively monitoring the enantiomeric composition of amino-acid derivatives and lactates in the gas phase. One sensor detects changes in mass, owing to binding of the compound being analysed (the 'analyte'), by thickness shear-mode resonance; the other detects changes in the thickness of a surface layer by reflectometric interference spectroscopys. Both devices use the two enantiomers of a chiral polymeric receptor, and offer rapid on-line detection of chiral species with high selectivity.

The discrimination of optical isomers (enantiomers) in the gas phase has been performed using two different analytical tools:  thickness shear mode resonators (TSMRs) and reflectometric interference spectroscopy (RIFS). The selective coatings included both enantiomers ((S)- and (R)-receptor) of a Chirasil-Val derivative (stationary phase material in GC) with octyl side chains. Successful discrimination of the enantiomers of different types of analytes (amino acids and lactates) was achieved. The results of both transduction methods were consistent and in good agreement with GC measurements. In addition, different mixtures of both enantiomers of the respective analyte were measured, and the enantiomeric composition could be quantitatively determined with excellent reliability. Since the sensors allow on-line monitoring (not possible with GC) of enantiomeric purity, an application in industrial synthesis (process control) of such compounds represents an interesting feature, especially with regard to the tested derivatives of lactic acid.

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We present a multiplexed fiber-optical sensor system for in-line monitoring ofvolatile organic compounds in air. The transducer consists of sensitive polymer films coated on glass substrates, a source of white light, a fibre-optical multiplexer and a photodiode array detector. It is based on the interferometric @hase sensitive) measurement of the change of optical parameters (thickness and refractive index) of the polymer film when exposed to volatile organic compound (VOCs) vapours. Polymer films swell fast and reversibly depending on the concentration of analyte in the vapour phase and the coefficient of distribution between ambient medium and polymer bulk. We shortly review the transducer's physical and chemical properties, and describe its applicability in sensor arrays, including internal referencing, and the perspectives in process control. This opens a way to rugged pattern recognition and multicomponent analysis of fairly complex mixtures of VOCs.