Related Experiment Video
Updated: May 20, 2026

Determination of Carbonyl Functional Groups in Bio-oils by Potentiometric Titration: The Faix Method
Published on: February 7, 2017
A new method for determining the acid number of biodiesel based on coulometric titration
Fabiano Barbieri Gonzaga1, Sidney Pereira Sobral
1Chemical Metrology Division, National Institute of Metrology, Quality and Technology, Av. Nossa Senhora das Graças, 50, Xerém, 25250-020, Duque de Caxias, RJ, Brazil. fbgonzaga@inmetro.gov.br
Abstract:
A new method is proposed for determining the acid number (AN) of biodiesel using coulometric titration with potentiometric detection, basically employing a potentiostat/galvanostat and an electrochemical cell containing a platinum electrode, a silver electrode, and a combination pH electrode. The method involves a sequential application of a constant current between the platinum (cathode) and silver (anode) electrodes, followed by measuring the potential of the combination pH electrode, using an isopropanol/water mixture as solvent and LiCl as the supporting electrolyte. A preliminary evaluation of the new method, using acetic acid for doping a biodiesel sample, showed an average recovery of 100.1%. Compared to a volumetric titration-based method for determining the AN of several biodiesel samples (ranging from about 0.18 to 0.95 mg g(-1)), the new method produced statistically similar results with better repeatability. Compared to other works reported in the literature, the new method presented an average repeatability up to 3.2 times better and employed a sample size up to 20 times smaller.
Related Concept Videos
Titration in Nonaqueous Solvents
Controlled-Current Coulometry: Coulometric Titration
The fundamental requirements for coulometric titrations are (1) 100% efficiency in the reagent-generating electrode reaction and (2) a stoichiometric and preferably rapid reaction between the generated...
Titration of a Weak Acid with a Strong Base
Titrimetric Methods: Types and Commonly Used Strategies
Titration of a Weak Acid with a Weak Base
As a result, there is no simple...
EDTA: Indirect and Alkalimetric Titration

