Abstract
Abstract Ascorbic acid is found in many food samples. Its clinical and technological importance demands an easy-to-use, rapid, robust and inexpensive method of analysis. For this purpose, this work proposes a new flow procedure based on the oxidation of ascorbic acid by periodate. A new potentiometric periodate sensor was constructed to monitor this reaction. The selective membranes were of PVC with porphyrin-based sensing systems and a lipophilic cation as additive. The sensor displayed a near-Nernstian response for periodate over 1.0 × 10 −2 –6.0 × 10 −6 M, with an anionic slope of 73.9 ± 0.9 mV decade −1 . It was pH independent in acidic media and presented good selectivity features towards several inorganic anions. The flow set-up operated in double-channel, carrying a 5.0 × 10 −4 M IO 4 - solution and a suitable buffer; these were mixed in a 50-cm reaction coil. The overall flow rate was 7 ml min −1 and the injection volume 70 μl. Under these conditions, a linear behaviour against concentration was observed for 17.7–194.0 μg ml −1 , presenting slopes of 0.169 mV (mg/l) −1 , a reproducibility of ±1.1 mV ( n = 5), and a sampling rate of ∼96 samples h −1 . The proposed method was applied to the analysis of beverages and pharmaceuticals.
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