Odorous compounds such as Volatile Organic Compounds (VOC) can be analysed by using GC-MS system. On the other hand, odour concentration or intensity can be measured with sensory olfactometer.

The principal barrier in linking analytical and sensory concentration measurements is the effect of mixtures. It would be advantageous to combine two or more different techniques, such as gas chromatography (GC) and olfactometry. The combination of measuring odour and odorants is called gas chromatography-olfactometry (GC/O) (Friedrich and Acree, 1998) or gas chromatography-olfactometry-mass spectrometry (Hochereau and Bruchet, 2004) more commonly called GC-MS-Sniffer. Its application to environmental odour analysis is only recent and has mainly focused on the measurement taste and odours (or off-flavours) in drinking water such as geosmin, however the approach in using GC-MS-Sniffer for odorant analysis is well established in other fields such as food aroma's (Fuller et al., 1964).

This technique allows odorants in gas samples to be separated and identified individually, and allows the odour contribution for each compound to be characterized and roughly quantified (Lewis et al., 2004).

During the measurement, an extracted sample is injected into a GC that is modified with an olfactometer at the detector end. The GC column effluent is split into two streams, one is routed to the mass spectrometer for producing a mass chromatogram, and another is directed to the olfactometer. A sniffer or human detectors will experience the character of the odour at the olfactometry outlet and record the response. The olfactometer allows the human subject to describe the specific odour characteristics and hedonic tone (agreeability) of each odorant, and also allows estimation of the odour intensity to be made using a seven step intensity scale (Lewis et al., 2004).

Examples of a GC-MS-Sniffer system are shown in Figure 10 (Thermal Desorber - Gas Chromatography - Mass Selective Detector - Olfactometer) and Figure 11 (Sample Injection - Gas Chromatography - Mass Detector - Sniffer).

Figure 10 TD-GC-MS-O (UNSW)

Figure 11 GC-MS-Sniffer

The measured data from GC-MS-Snifferr systems is often expressed as odour dilution response chromatogram, odour spectrum chromatogram, odour activity value and can be used to produce odour wheels (Suffet et al., 1999) which relate to odour descriptors to the chemical composition of odorants (Figure 12).

Figure 12 Odour wheel for taste and odour in drinking water (Suffet et al., 1999)