Identification of off-odor compounds

The threshold limits of chemical compounds can lie over a range of 10 orders of magnitude or more (Table 13-3). The saturated hydrocarbons and organic solvents have high threshold limits and are as a consequence relatively odorless. Esters of acrylic acid and a,fl-unsaturated ketones and aldehydes belong to intensive aroma compounds. 

Descriptions of several methods of analysis are given in the following because of their relationship to sensory properties. These methods are not applied for the simple case mentioned in the introduction where a specific substance is studied and only its quantitation is of interest. 

10° Butylacetate, Vinylacetate, Acetic acid. Acrylic acid, 2-Ethylhexylmethacrylate, 2-Ethyl- 

The odor compounds retained on a sorbant are desorbed with a volatile solvent, e.g. ether, and after concentrating the solution are separated with a gas chromatograph (GC). It is necessary in this case to split the carrier gas stream coming off the column into two streams. One stream is directed to a mass spectrometer or other physical detector (Fig. 13-1) and the other stream is available for sniffing. With this detection method three cases shown in the figure can occur  

One obtains a physically detectable signal but no odor impression at the same retention time. 

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