Chemical/Petrochemical Article

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 analysis; 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 quantified. These results confirm the Rtx®-Biodiesel column is a wise choice for biodiesel oil analysis according to DIN EN14105 conditions. 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 standards butanetriol and tricaprin, silylated the mixture 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® constriction; 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 regarding biodiesel oil analysis, please call our technical service team, or contact your Restek distributor, for fast and reliable assistance.

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