Routine high-performance liquid chromatographic determination of ascorbic acid in foods using L-methionine for the pre-analysis sample stabilization

The possibility of use of phosphoric acid (0.2% v/v, pH 2.1) in the mobile phase and co-existing compounds present in foods as the dissolving agent for the pre-analysis sample stabilization were examined for the routine determination of ascorbic acid (AA) in foods by high-performance liquid chromatography (HPLC) with electrochemical detection (ED). The applied potential was set at 400 mV versus an Ag/AgCl reference electrode. It was demonstrated that 0.2% v/v phosphoric acid was the useful mobile phase and L-methionine was the most effective dissolving agent for the pre-run sample stabilization of AA in foods after comparison with other amino acids and water-soluble vitamins. The proposed method was simple, rapid (retention time @ ca. 4 min), sensitive (detection limit: ca. 0.1 ng per injection (5 mul) at a signal-to-noise ratio of 3), highly selective and reproducible (relative standard deviation (R.S.D.); 2.5% (n = 7), between-day R.S.D.: 3.7% (5 days)). The calibration graph of AA was linear in the range of 0.1 - 12.5 ng per injection (5 mul). Recovery of AA was over 90% by the standard addition method. Relationship between structure of compounds and the stability of AA was also examined. (C) 2003 Elsevier Science B.V. All rights reserved.