Improved determination of malonaldehyde by high-performance liquid chromatography with UV detection as 2,3-diaminonaphthalene derivative

• Malonaldehyde (MA) is a marker used to follow lipid oxidation phenomena in food.
• MA reacted with 2,3-diaminonaphthalene giving a product suitable to HPLC-UV.
• The UV response was better than that obtained by MA with 2,4-dinitrophenylhydrazine.
• The method were optimized with respect to the longer previously reported one.
• The method was applied to estimate free MA in commercial canned mackerel fillets.

A rapid, specific and simple procedure is proposed for the determination of free malonaldehyde (MA) contained in fish tissue. The method is the optimization of the reaction of MA with 2,3-diaminonaphthalene to afford a naphtodiazepinium ion that present a UV absorption at 311 nm, useful for MA determination by HPLC with UV detection. The reaction proceeds in the presence of 25% acetonitrile at 37 °C in 20 min at pH 2 using 2,4-pentanedione as internal standard. The method has been applied to homogenized samples of canned mackerel fillets that were treated with 2,3-diaminonaphthalene in an acidic aqueous:acetonitrile mixture. The produced naphtodiazepinium ion was extracted in acetonitrile by a salting-out homogeneous liquid–liquid extraction. A standard calibration was carried out in the range 0.625–10 nmol/g. The reliability of the procedure is demonstrated by linearity (r2 = 0.998), limit of detection (0.16 nmol/g), limit of quantification (0.22 nmol/g), repeatibility (RSD 5.57%), and intermediate precision (RSD 8.92%).