Threshold values pyridines

There are some circumstances where permanent ventilation cannot be installed to remove solvent fumes and the only method to make an atmosphere fit to breathe is by providing so much ventilation air that the solvent vapours will be diluted to a safe level. This will not necessarily produce pleasant working conditions since safe dilution is based on TLV and vapour pressure. A solvent (e.g. pyridine) with a very low odoiu threshold may have a nasty smell at a concentration well below its TLV as the values for odour safety factor indicate. 

This characteristic feature appears to be required for a roasted odor. In fact, aU the pyrroUnes and pyridines listed in Table 5.23 as weU as 2-acetyl-thiazole, 2-acetylthiazoline (cf. Table 5.22) and acetylpyrazine (cf. Table 5.23) contain this structural element and have a roasted or cracker-hke odor. However, the thresholds of these compounds vary greatly. The lowest values were found for 2-acetyl-and 2-propionyl-l-pyrrohne. The length of the alkanoyl group also influences the aroma activity because in the transition from 2-propionyl- to 2-hutanoyl-l-pynoline, the roasted note suddenly disappears and the odor threshold increases hy several powers of ten. 2-Acetyl-l-pyrrohne (Apy) is responsible for the typical aroma of the cmst of white bread and it... 

The effect of the emitter surface temperature, electric field and gaseous environment around the emitter on the analyte response should be considered. Figure 3 shows the curve of i T) for ions with mass [M -t H] of pyridine in ASI, with [M - H] of xylene in DSI, and with M of aniline in MSI [11]. An ionization threshold temperature (7),) was observed around 400°C, which is compound dependent. The To value for all the compounds is less than T (475°C) for the appearance of sodium ions (Na ) and potassium ions (K ) from Na and K impurity atoms in Re. The i versus T curve for aniline resembles that for the ionization... 

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