Amperometric determination of nitrite based on reaction with 3-mercaptopropanoic acid

The measurement of nitrite is based on the electrochemical reduction at gold electrode of thionitrite, which is the product of reaction between nitrite and 3-mercaptopropanoic (MPA). Visible absorption spectra show that S-N=O of thionitrite is involved in the electrochemical reduction at the gold electrode. The result of coulometric analysis indicates that the electrochemical reduction is a two-electron transfer process. The dependence of peak potential on pH provides evidence that two protons are involved in the electrochemical reaction. A mechanism for the reaction is proposed. The effect of MPA concentration on the current response in the presence of nitrite is also discussed. The detection limit is 5 mu mol/l and the peak current is linear with the concentration of nitrite over the 5x10(-6)-5x10(-3) mol/l range. This method is used for the determination of nitrite in pickled vegetable water and the results are satisfactory. (C) 1999 Elsevier Science B.V. All rights reserved.