COON
COON
fling cleavage
COOH
OH
Monohydroxyphthalic acids
COON
COON Series of aliphatic oxidation COOH_products containing 1-4 carbon atoms Muconic acid
Fig. 6. Degradation scheme for plilltalic acid, by °zonation in aqueous solution
From these results we are able to propose a degradation scheme for plithalic acid by °zonation in aqueous solution (Fig. 6) involving two main reaction pathways, the first being hydroxylation of the aromatic ring, leading to the formation of monohydroxyphthalic acids, and the second decarboxylation of a carboxyl group to give salicylic acid and dihydroxybenzoic acids after hydroxylation of the salicylic acid. These two oxidation patterns are associated with ring cleavage to give muconic acids and a series of very polar short-chain oxidation products.
The technique of combined reversed-phase F IPLC - MS is useful for the analysis of model water samples containing a limited number of unknown organic pollutants, and where a reasonable separation of the products is possible. This technique avoids such procedures as extraction and derivatisa-tion, and can complement gas chromatography - mass spectrometry for the analysis of non-volatile or thermolabile compounds. The sensitivity of the system is reduced by the small amount of the total eluate (1%) that enters the mass spectrometer source. The concentration of the 4-hydroxyphthalic acid, for example, was about 2.5 lig in1-1 in the ozonised solution. It was necessary to concentrate this solution 20-fold in order to observe a distinct signal in the total ion current chromato-gram. Efforts must be made towards improving sensitivity, increasing the mass spectrometry fragmentation and addition reaction data for the various commonly used liquid chromatography solvent systems and mass spectrometry working parameters.
The authors are grateful to Mr. Y. George, Analytical Instruments Division, I lewlett-Packard, France, for his help and instrument facilities.
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