2.3. Analytical methods
The fatty acid profile of the vegetable oil was measured following
the International and European Standards ISO 5509 (to prepare
the methyl esters) and EN 14103 (to measure the methyl esters
profile), using a HP 6890 Series II Gas Chromatograph with a flame
ionization detector. The capillary column was a DB-WAX column
with a length of 30 m, a film thickness of 0.25 lm and an internal
diameter of 0.32 mm. Helium was used as carrier gas and also as an
auxiliary gas for the FID. One micro-litre of sample was injected
using a 6890 Agilent Series Injector (Knothe et al., 2005).
Kinematic viscosity was measured with a Canon-Fenske capillary
viscosimeter immersed in a constant temperature (40 C) bath
(TAMSON TV 2000) following the European norm EN ISO 3104.
Acid value is expressed in mg KOH required to neutralize the
free fatty acids present in 1 g vegetable oil. The procedure involves
titration of the diluted sample with ethanolic potassium hydroxide
solution using a Metrohm 702 SM Titrino. This procedure was
developed according to ISO 660.
The phosphorus content was measured following the European
norm UNE 14107, using a Varian 710-ES Optical Emission Spectrometer
with inductive coupled plasma (ICP).
Peroxide value is a measure of the concentration of peroxides
and hydroperoxides formed in the initial stages of lipid oxidation.
Milliequivalents of peroxide per kg of fat are measured by titration
with iodide ion following the European norm UNE 55-023-73.
Oxidative stability expresses the susceptibility to oxidation
upon exposure to air of oil. Metrohm 743 Rancimat was used to
determinate the induction period. This procedure was developed
according to UNE 55-116-75. Oxidative stability of alkyl esters
was measured following the European Norm UNE 14112.
Iodine value was measured by titration in a Metrohm 702 SM
Titrino following the European standard UNE-EN ISO 3961.
Specific extinctions at 232 and 270 nm were determined using a
Shimadzu UV 1700 PharmaSpec spectrometer. Samples were diluted
with cyclohexane to bring the absorbance within limits
(0.1–0.8).
Determination of tocopherol and tocotrienol were measured
according to the official method of the American Oil Chemist Society
(AOCS Ce 8-89), using an Agilent Technologies Series 1100
HPLC with a fluorescence detector (Thermo-Finnigan FL 3000).
Cold filter plugging point (CFPP) test calls for cooling a FAME
sample at a specified rate and drawing it under vacuum through
a wire mesh filter screen. CFPP is then defined as the lowest temperature
at which 20 mL of sample safely passes through the filter
within 60 s. An automatic tester ISL FPP 5Gs was used to carry out
the determination of the CFPP.
Thermal analytical methods such as subambient differential
scanning calorimeter (DSC) were successfully applied to neat
petrodiesel and engine oils. DSC analyses were conducted in a
differential scanning calorimeter model DSC Q100 of TA.Thecrystallization onset temperatures was determined by rapidly
cooling the sample, equilibration to 70 C, then heating from
40 to 40 C at 5 C/min and cooling from 40 to 40 C at 5 C/min