Analytical Sciences

Nickel-Chromium Electrode as a Detector in Flow-Injection Amperometry: Determination of Glycerol

Ivanildo Luiz de MATTOS, Denise MELO and Elias Ayres Guidetti ZAGATTO *

Centro de Energia Nuclear na Agricultura, Universidade de Sao Paulo, P.O. Box 96, Piracicaba-SP 13400-970, Brazil

A flow-injection amperometric method for glycerol determination in samples relevant to the industrial production of soaps, detergents and such is presented. A nickel-chromium alloy micro-cylindric electrode was used as the electrochemical detector, which after a pretreatment exhibited good repeatability and stability. The method involved glycerol oxidation by an inactive Ni(OH)₂ surface film to a Ni(III) layer, usually described as NiOOH (formed in the range from 0.40 to 0.50 V vs. Ag/AgCl), and reduction back to the starting hydroxide. The influence of sodium hydroxide (0.1 - 1.0 mol l^-1) and potassium chloride (0.5 - 3.0 mol l^-1) concentrations and sample-injected volume (10 - 100 ml) on the linear dynamic range, stability and response time of the electrode were evaluated. The proposed system handles about 60 samples per hour and is very stable and suitable for industrial control. Results within 20 and 80%(w/v) glycerol are precise (rsd <2%) and in agreement with the conventional procedures. (Keywords: Glycerol, nickel-chromium alloy, cyclic voltammetry, flow-injection, amperometry)

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