Fausto Munari, Daniela Cavagnino and Andrea Cadoppi, Thermo Fisher Scientific, Milan, Italy.
Interest in biodiesel as a clean-burning alternative fuel produced from renewable sources such as vegetable oils has increased
tremendously over the last few years, mainly because of its reduced environmental impact in comparison with conventional petro-diesel.
Biodiesel can be used as a pure fuel or blended at any level with petroleum diesel. For biodiesel to be commercialized as
pure biofuel or blending stock for heating and diesel fuels, it must meet a set of requirements as defined in ASTM D6751 and
EN 14214 standards. These standards indicate maximum allowable concentrations of contaminants in B100 finished product, along
with other chemical-physical properties necessary for safe and satisfactory engine operation.1
One indicator of biodiesel quality is free and bonded glycerine content. Low levels of total glycerine ensure high conversion
of the oil, while high levels of glycerine and glycerides can cause injector deposits, clogged fuelling systems and poor cold
weather operation. The analysis of glycerine, mono, di and triglycerides by gas chromatography requires a non-discriminative
injection system able to transfer both volatile and heavy compounds without discrimination or degradation. This application
describes the use of the Thermo Scientific TRACE GC Ultra for the analysis of free and total glycerine according to EN14105.2
Experimental ConditionsA TRACE GC Ultra equipped with a cold on-column inlet and a flame ionization detector (FID), with automated injections performed
by a TriPlus Autosampler, was used for this study. The analytical column was a Thermo Scientific TRACE TR-Biodiesel (10 m
× 0.32 mm i.d. 0.1 μm f.t.), with a 1 m × 0.53 mm i.d. pre-column. For the connection between the pre-column and the analytical
column, a low dead volume leak-free metal tee was developed that provides long-term reliability even at elevated temperatures.
The TRACE GC Ultra was programmed as follows: initial temperature 80 °C, hold for 1 min, ramp at 15 °C/min to 180 °C, no hold,
ramp at 7 °C/min to 230 °C, no hold, ramp at 10 °C/min to 365 °C, hold for 4 min. The TriPlus was programmed to inject 1 μL
on-column. Using an automated system for performing the on-column injections allowed enhanced productivity.
Results
Figure 1
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A typical chromatogram for Biodiesel is shown in Figure 1. Calibration is achieved by the use of two internal standards —
1,2,4-butanetriol (IS1) for glycerine and tricaprin (IS2) for mono, di and tri-glycerides, and four reference compounds —
glycerine, mono-olein, di-olein and tri-olein. Total glycerine is calculated as the sum of free glycerine plus a percentage
of total mono-, di-and triglycerides, as indicated in EN14105. System linearity and repeatability complied with the requirements
of EN14105.
Conclusion
With increasing interest in biodiesel production, the issue of product quality is an ongoing concern.
The TRACE GC Ultra provides simple and reliable determination of free and total glycerine in pure biodiesel, in full compliance
with the EN specifications. The true cold on-column injector offered on the TRACE GC Ultra prevents discrimination of the
heavier fraction, and eliminates any risk of degradation of labile components like triglycerides, thus granting excellent
recovery and proven sample integrity. Automation of on-column injections ensures increased productivity for performing this
analysis.
References
1. EN14214: Standard specification for biodiesel fuel blend stock (B100) for middle distillates fuels.
2. EN14105: Test method for determination of free and total glycerine in B-100 biodiesel methyl esters by gas chromatography.
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Website: http://www.thermo.com/gc/
