Flame CARS measurements performed

In addition to temperature measurements, the gas-phase CARS technique also provides information on the fluctuating properties occuring for instance in turbulent combustion systems. However, concentration measurements are more difficult to perform than temperature ones because the absolute intensity is required, while temperature measurements are only based on the shape of the spectrum. Simultaneous information on the relative concentrations between several species are easier to obtain. For such investigations the technique called dual broadband CARS has been introduced by Eckbreth and Anderson (1985) which allowed the researchers to simultaneously generate CARS spectra of CO2, N2 and H2O in the postflame zone of a premixed C2H4-air flame. 

In the early 90s, a new technique called solid-phase-micro extraction (SPME), was developed (Arthur and Pawliszyn, 1990). The key-part component of the SPME device is a fused silica fiber coated with an adsorbent material such as polydimethylsiloxane (PDMS), polyacrylate (PA) and carbowax (CW), or mixed phases such as polydimethylsiloxane-divinylbenzene (PDMS-DVB), carboxen-polydimethylsiloxane (CAR-PDMS) and carboxen-polydimethyl-siloxane-divinylbenzene (CAR-PDMS-DVB). The sampling can be made either in the headspace (Vas et al., 1998) or in the liquid phase (De la Calle et al., 1996) of the samples. The headspace sampling in wine analyses is mainly useful for quantifying trace compounds with a particular affinity to the fiber phase, not easily measurable with other techniques. Exhaustive overviews on materials used for the extraction-concentration of aroma compounds were published by Ferreira et al. (1996), Eberler (2001), Cabredo-Pinillos et al. (2004) and Nongonierma et al. (2006). Analysis of the volatile compounds is usually performed by gas chromatography (GC) coupled with either a flame ionization (FID) or mass spectrometry (MS) detector. 

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