A search for the cause of Edmonton's spring time taste and odour events occurring in two successive years implicated four low molecular weight aldehydes: 2-methyl propanal, 2-methyl butanal, 3-methyl butanal and phenylacetaldehyde. Food science literature reports threshold odour values at µ.g/l levels for these chemicals. Observations of a more intense odour in treated than in raw water suggested the possibility of these compounds being produced in the treatment process. The chemistry literature suggests the likelihood that these chemicals could arise as oxidation products of corresponding amino acids. This expectation has been experimentally confirmed for chlorination and chloramination of water supplies.
Low molecular weight aldehydes have been quantitatively measured in distilled water at levels similar to their published threshold odour concentrations by a simple and sensitive purge and trap method. Isobutyraldehyde, isovaleraldehyde and 2-methylbutyraldehyde were isolated from aqueous samples by purge and trap onto Tenax-TA m adsorbent. The aldehydes were thermally desorbed onto the head of a cryogenically cooled gas chromatography column and eluted by temperature programmed gas chromatography. The method has a linear range of 0.5 μg -1 to 100 μgL -1 with an average precision of 10.9% relative standard deviation for the aldehydes studied.
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