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2007.01
Chemical/Petrochemical
Biodiesel Analysis by European Methodology
Exceptional Peak Symmetry, Using an Rtx®-Biodiesel GC Column
By Barry L. Burger, Petroleum Chemist
• Excellent peak shape, even for free glycerin.
• Low column bleed at >350°C.
• Quantify oil components more easily and more reliably.
In less than a decade biodiesel oil has become a significant fuel source, especially in European countries, where current usage has
soared to 1,800,000 tons annually.1 Transesterification of the rapeseed oil or other fats from which biodiesel oil is prepared yields two
products: methyl esters – biodiesel oil – and glycerin. Glycerin is extremely challenging to analyze by GC, but because excessive
amounts in biodiesel products can cause problems during storage or in the engine it is necessary to monitor glycerin levels. In the
US, American Society for Testing and Materials (ASTM) Method D6584-00e1 is an accepted GC procedure for biodiesel oil analy-
sis; the standard European method is Deutsches Institut fur Normung (DIN) EN14105. Both methods set limits on free glycerin and
glycerides in biodiesel oil product. While these methods differ in GC column specifications and chromatographic conditions, both
require a column that can perform reliably at elevated temperatures, with minimal bleed.
Figure 1 shows the chromatography for the DIN analysis, using an Rtx®-Biodiesel column. Peaks for glycerin and the glycerides
exhibit minimal tailing, and bleed is low, even at 370°C. Thus, components of the oil can be more easily and more reliably quanti-
fied. These results confirm the Rtx®-Biodiesel column is a wise choice for biodiesel oil analysis according to DIN EN14105 condi-
tions. The Rtx®-Biodiesel column also has proven well suited for analyzing biodiesel oil according to the ASTM method.2
To obtain Figure 1, we spiked a soybean oil-based
sample of B100 biodiesel oil with internal stan-
dards butanetriol and tricaprin, silylated the mix-
ture with MSTFA and, using simple on-column
injection mode, injected a 1µL aliquot into a low
dead volume direct injection liner in a Shimadzu
2010 GC equipped with an on-column injector
(OCI). The liner has a 1mm internal diameter and
a Press-Tight® constriction one-third of its length
from the outlet end. The Rtx®-Biodiesel column
forms a seal with the liner at the Press-Tight® con-
striction; the sample is injected into, and vaporizes
in, the top two-thirds of the liner.
Glycerin is a notoriously difficult challenge in GC,
particularly at the levels involved in biodiesel oil
analysis, yet an Rtx®-Biodiesel column provides a
symmetric peak that makes quantification easier
and more reliable. Restek chromatographers
always are happy to help you with your toughest
analytical problems. If you have questions regard-
ing biodiesel oil analysis, please call our technical
service team, or contact your Restek distributor, for
fast and reliable assistance.
References
1.
2. Restek Advantage 2006.04, pp 3-5 (2006).
Reference 2 available from Restek – request lit. cat.# 580120.
Figure 1 Biodiesel oil analysis using an Rtx®-Biodiesel column
and DIN EN14105 conditions: peaks for glycerin and glycerides are
symmetric, and bleed is low, even at 370°C.
GC_PC00901
Column: Rtx® -Biodiesel, 10m, 0.32mm ID, 0.10µm (cat.# 10292)
Sample: B100 biodiesel oil plus butanetriol and tricaprin, in heptane, derivatized with MSTFA
Inj.: 1µL onto Shimadzu on-column injector (OCI) equipped with low dead volume
Shimadzu direct injection liner
Inj. temp.: oven track
Carrier gas: hydrogen, constant flow
Flow rate: 4mL/min.
Oven temp.: 50°C (hold 1 min.) to 180°C @ 15°C/min., to 230°C @ 7°C/min., to
370°C @ 10°C/min. (hold 5 min.)
Det.: FID
Det. temp.: 390°C
glycerin
butanetriol (IS)
tricaprin (IS)
triglycerides
diglycerides monoglycerides
Rtx®-Biodiesel Column (fused silica)
ID df (µm) temp. limits length cat. # price
0.32mm 0.10 330º/380ºC 10-Meter 10292 $245
did you know?
We also offer biodiesel calibration standards.
For more information visit us online at
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