The characterisation of thiobarbituric acid reactivity in human plasma and urine.

The specificity of the thiobarbituric acid reaction (TBA) has been investigated using techniques of high-performance thin-layer chromatography and spectrofluorimetry. It was found that malondialdehyde (MDA) derived from different lipid and nonlipid origins formed the same MDA-TBA complex. This complex could be separated from other TBA-reactive compounds by both chromatography and spectrofluorimetry. Normal human plasma and urine both formed an MDA-TBA complex along with other TBA-reactive compounds. In plasma this was associated mainly with phosphatidylcholine and appeared to be peroxidic in reaction. Urine, however, contained polar MDA-forming compounds probably resulting from the oxidation of 2-deoxyaldoses during the acid-heating stage of the TBA test.