International Conference on Metrology of Environmental, Food and Nutritional Measurements
two scientific events at the same place and time
2nd IMEKO TC19 Conference on Environmental Measurements
1st IMEKO TC23 Conference on Food and Nutritional Measurements
10 – 12 September 2008, Budapest, Hungary
METROLOGICAL EVALUATION OF TITRATION TECHNIQUES FOR THE
DETERMINATION OF THE IODINE VALUE IN BIODIESEL
R. V. P. Leal 1, P. P. Borges 2, P. R. Seidl 3
1 Inmetro, Rio de Janeiro, Brasil, email@example.com
2 Inmetro, Rio de Janeiro, Brasil, firstname.lastname@example.org
3 Federal University of Rio de janeiro, Rio de Janeiro, Brasil, email@example.com
Abstract: Based on international standard procedures, the
degree of unsaturation on biodiesel was evaluated, called
iodine value. Two titration techniques were used to
determine the iodine value: colorimetric and potentiometric
techniques. The uncertainty of measurement was used to
evaluate the quality of the results.
The potentiometric technique showed better quality
in the determination of the iodine value because of its
accuracy as well as lower uncertainty result of the
measurements, with values between 0,613 g I2 / 100 g and
1,438 g I2 / 100 g), compared to the results from the
colorimetric technique, with values between 1,61 g I2 / 100 g
and 3,30 g I2 / 100 g.
The specification of biodiesel (B100) establishes the
degree of unsaturation which is present in its composition,
or its iodine value, which is related to factors in the quality
of the biodiesel fuel, such as polymerization, stability and
viscosity. The unsaturated fatty acids are susceptible to the
oxidation reactions, which can be accelerated by the
exposition to oxygen and high temperatures. Thus, they are
able to result in polymeric composites and gum formation,
influencing in the performance of the engine for the increase
of viscosity and acidity, capable of generating corrosive
The standard procedures use colorimetric titration,
with a starch indicator, as the main method for iodine value
measurement. Some of them also mention potentiometric
titration as an alternative.
Related to the accurate measurement of the biodiesel
quality parameter, the National Institute of Metrology –
Inmetro has been developing research activities aiming at
the production of certified reference materials for biodiesel.
Therefore, Inmetro needs to use adequate methods of
measurement to be adopted in the analyses, providing
guarantee and reliabity to the results.
Based on the standard procedures, a comparison of
the techniques was developed to determine the end point of
titration, either potentiometric or colorimetric. The
experiments were conducted varying the solvent for
dissolution of the biodiesel, either carbon tetrachloride or
cyclohexane / glacial acetic acid (1:1) and the temperature
of reaction, either 25 °C or 37 °C. The experiments were
performed on a biodiesel matrix from palm oil. The quality
of the measurements was evaluated through the uncertainty
of each result in accordance with the described method in
Eurachem Guide .
The experiments were carried out by using biodiesel
B100 of the palm oil produced from the esterification
process of fatty acid. All reagents were of analytical degree.
The water used in the preparation of the solutions was
deionized water by Milli-Q® system.
The potenciometric titrations were carried out by
using platinum ring electrode, model 6.0431.100 Pt Tirode
(Metrohm), connected to an automatic titrator, model Titrino
756 (Metrohm) with the use of software Tinet 2.5. The
colorimetric titrations were carried out in burette of 10 mL,
with 0,02 mL as the value of each division.
The methodology had its starting point in the
assessment of the techniques of titration in national and
international standards for measuring the iodine value.
The potentiometric titrations, whose end point was
determined by changes in the electrode potential, were
performed using a combined electrode of platinum ring
coupled to an automatic titrator with burette of 20 mL and
resolution of 0.0001 mL. The colorimetric titrations were
performed using burette glass of 10 mL, with value of each