Flow-injection analysis for malondialdehyde in plasma with the thiobarbituric acid reaction.

A simple, precise, and rapid method to measure plasma malondialdehyde (MDA) was developed by use of solvent extraction--flow-injection analysis. The reagent solution, containing thiobarbituric acid (TBA), 5 g/L in 100 mL/L phosphoric acid, and extraction solvent (methylisobutyl ketone, MIBK) were propelled with a double-plunger micropump at a flow rate of 0.3 mL/min, and 20 microL of sample was introduced into the reagent stream. After TBA-MDA reactant was extracted into MIBK, the organic phase was continuously separated by a successive phase-separation system equipped with two phase separators, and the absorbance of the TBA-MDA reactant was measured at 532 nm. This approach resulted in excellent sensitivity, a CV of < 1.5%, a good correlation with the conventional manual method, and a sampling frequency of 7 samples/h, suggesting that this semiautomated method is suitable for measuring plasma MDA.