Real-time detection of L-ascorbic acid and hydrogen peroxide in crude foodsamples employing a reversed sequential differential measuring technique of the SIRE-technology based biosensor

Detection of the common electrochemical interferents, ascorbic acid and hyd rogen peroxide, using a SIRE (Sensors based on Injection of the Recognition Element) technology based biosensor in reverse mode operation is reported. The differential measuring principle employed in the SIRE biosensor during operation in reverse mode is such that the sample is measured first in the presence of enzyme (yielding matrix signal only), and then measured again in the absence of enzyme (yielding signal from matrix + analyte). Subtracti on of the signal obtained in the presence of enzyme from the signal obtaine d in the absence of enzyme gives a specific signal for the analyte only and correlates directly to its concentration in solution. The linear range for the determination of ascorbic acid and hydrogen peroxide was 0-3 mM and 0- 2 mM, respectively, with an enzyme concentration of 25 U ascorbate oxidase/ ml and 1000 U catalase/ml. The reproducibility was 5% for ascorbic acid (R. S.D. n = 15) and 10% for hydrogen peroxide (R.S.D. n = 18). The cost per me asurement was 0.28 USD for ascorbic acid analysis and 0.0008 USD for hydrog en peroxide analysis. The degradation of ascorbic acid in cereal was follow ed in real-time, as was the stabilization of low pH on the degradation proc ess. (C) 2001 Elsevier Science BY. All rights reserved.