Optimization of the thiobarbituric acid-malonaldehyde reaction in non-aqueous medium. Direct analysis of malonaldehyde in oil samples by HPLC with fluorimetric detection

The reaction of thiobarbituric acid (TBA) with saturated and unsaturated aldehydes in organic medium, 1-propanol, compatible with lipid samples, has been studied using spectrophotometric and fluorimetric techniques. With saturated aldehydes, the formation of non-fluorescence yellow derivatives was observed. Unsaturated mono-aldehydes, trans, trans-2,4-hexadienal and trans, trans-2,4-nonadienal, give fluorescent TBA-derivatives. In presence of malondialdehyde (MDA), a derivative with an absorption maximum located at 532 nm and a fluorescence maximum located at 552 nm, exciting at 532 nm, were observed. The structures of the derivatives generated in organic medium were achieved by high performance liquid chromatography (HPLC) using a mass spectrometer as detector. A heterogeneous propanol-water-oil medium was optimized for the direct analysis of MDA in oil samples by HPLC with fast scanning fluorescence detection. Good linearity over the range of 0.05–1.0 μg mL−1 was obtained. Without any pre-treatment, olive oil and dermatologic oil samples were analysed. MDA was selectively determined in presence of other potential TBARs. The proposed HPLC-fluorimetric method is more selective than the spectrophotometric method because only MDA, and no other TBARs, is determined.