Flow injection spectrophotometric determination of L-ascorbic acid in pharmaceutical formulations with on-line solid-phase reactor containing copper (II) phosphate

An improved FIA-spectrophotometric method is proposed for the determination of ascorbic acid in pharmaceutical formulations by exploiting the reproducibility and stability of a solid-phase reactor containing copper(II) phosphate immobilized in a polymeric matrix of polyester resin. This determination is accomplished by the reduction of Cu(II) ion to Cu(I), which is transported to the liquid phase (acetate buffer (pH 4.5) carrier) and subsequently detected by monitoring the absorbance signal of the chelate produced in the reaction between Cu(I) and bathocuproine at a wavelength of 480 nm. The calibration graph for ascorbic acid was linear over the concentration range from 5.0x 10(-6) mol l(-1) to 4.0 x 10(-5) mol l(-1) with a correlation coefficient of 0.9998. The detection limit (three times the signal blank/slope) was 3.0x 10(-7) mol l(-1) of ascorbic acid. The relative standard deviation was 0.75% for a solution containing 2.0x 10(-5) mol l(-1) ascorbic acid (n =10) and 80 results were obtained per hour. The recovery of ascorbic acid from six samples ranged from 97.3% to 103.4% of the added amount. The results obtained for ascorbic acid by the proposed FIA-spectrophotometric method are in very close agreement with those obtained using the Pharmacopeia method. (C) 1998 Elsevier Science B.V.