Critical aspects of the determination of pentafluorobenzyl derivatives of aldehydes by gas chromatography with electron-capture or mass spectrometric detection: Validation of an optimized strategy for the determination of oxygen-related odor-active aldehydes in wine.

This work presents a thorough study of some aspects critical to the quantitative performance of methods for the determination of volatile aldehydes previously derivatized to pentafluorobenzyl hydroxylamine oximes. The conclusions of the study are further applied to the validation of an optimized procedure for the determination of oxidation-related aldehydes from wine. Aspects studied include the chromatographic injection, the analytical performance of electron-capture detection (ECD) or MS detection, and the way in which the derivatization is carried out. Different injection techniques have been optimized and compared (classical splitless-hot injection; cold splitless; and large volume solvent split injection). All of them were carried out in a programmed temperature vaporization (PTV) injector, with a 350 microL internal volume liner (3.4 mm internal diameter). Classical splitless injection of hexane extracts is troublesome and requires large carrier gas flows (>10 mL min(-1)). Cold splitless injection was clearly superior. Large volume solvent split injection has been also optimized. ECD has been found to lack the necessary selectivity for the determination of unsaturated aldehydes in wine, although the quantitation of several minor aldehydes is possible. MS detection has proven to be superior for the determination of these compounds in wine. The way in which the reagent is applied is also critical and for the case of wine is important to ensure that the reagent is applied after some of the major wine aldehydes have been eliminated. The finally proposed method is extremely sensitive. Method detection limits ranged from 0.002 microg L(-1) (for unsaturated aldehydes) to 0.73 microg L(-1) (for phenylacetaldehyde) and precision (measured as relative standard deviation) is < or =6% in all cases. The method makes it possible to determine quantitatively in a single run the wine aldehydes with sensory significance (isobutyraldehyde, 2-methylbutanal, isovaleraldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methional and phenylacetaldehyde).