208 / 413
Figure 2
Derivatized B100 samples resolve well on the 15m x
0.32mm MXT®-Biodiesel TG column, which is factory coupled to a
0.53mm retention gap using an Alumaseal™ connector.
•
10
•
2008 vol. 1
Chemical/Petrochemical
0
10
20
Time (min)
Column:
MXT
®
-Biodiesel TG, 15m, 0.32mm ID, 0.10µm (cat.# 70291) with
a 2m x 0.53mm MXT
®
retention gap connected with an
Alumaseal™ connector (17m total length)
Sample:
biodiesel (B100), derivatized
Inj.:
cool on-column injection
1µL in heptane
Inj. temp.:
oven track
Carrier gas:
hydrogen, constant flow
Flow rate:
3mL/min.
Oven temp.:
50°C (hold 1 min.) to 180°C @ 15°C/min. to 230°C @ 7°C/min. to 380°C @
30°C/min. (hold 5 min.)
Det.:
FID @ 380°C
GC_PC00968
Glycerin
butanetriol (IS)
tricaprin (IS)
Monoglycerides
Monoglycerides
Diglycerides
Triglycerides
Comparing Fused Silica and Metal Columns
Fused silica columns traditionally have been used
for GC biodiesel analysis, but metal columns offer
significant performance advantages. How can ana-
lysts determine which column is best for their lab?
Here we compare fused silica and metal column
performance for total glycerin analysis of biodiesel
and offer guidelines for column selection.
Excellent chromatography can be obtained using
Rtx®-Biodiesel TG fused silica columns. However,
for high temperature work (>380°C) metal
columns are much more rugged because the poly-
imide resin used to make fused silica hardens at
high temperatures, making columns brittle and
producing active sites in the column. To maximize
column lifetime, tubing choice should be based on
the maximum temperature setting in the GC tem-
perature program. If the temperature programwill
be 400°C or lower, high temperature fused silica
tubing is an acceptable choice; for GC tempera-
tures that will exceed 400°C, metal tubing should
be used.
Rtx®-Biodiesel TG Fused Silica Columns
Two fused silica GC column dimensions are available
for the analysis of total glycerin: 10m x 0.32mm ID
or 15m x 0.32mm ID, both of which are connected
to a 2m x 0.53mm ID retention gap for cool on-
column injection. The retention gap is factory
coupled using Restek’s unique Alumaseal™ con-
nector (Figure 1). This innovative connector is
leak-tight and low dead volume, making it advan-
tageous for high temperature work.
Metal Column Solutions: Two Options
for Increased Stability and Performance
• 0.32mm MXT®-Biodiesel TG columns with
factory-connected retention gaps.
• 0.53mm MXT®-Biodiesel TG columns with
built-in retention gaps.
The primary advantage of using metal MXT®
columns is that they are more stable at high tem-
peratures than fused silica columns. This means
they will exhibit lower bleed, improving analytical
performance, and have longer lifetimes, making
them a cost-effective option. High temperature
tolerance also means these columns can be brought
to high temperatures (430°C) allowing nonvolatile
material to be baked off of the column. MXT®-
Biodiesel TG columns are available in the same
dimensions as their fused silica counterparts:
Selecting a GC Column for Glycerin in Biodiesel
By Barry Burger, Petroleum Innovations Chemist, and Gary Stidsen, Product Marketing Manager
• Choose metal MXT®-Biodiesel TG columns for high temp. conditions; low bleed and leak-proof for more accurate results.
• Use Rtx®-Biodiesel TG columns up to 380°C when fused silica is desired; reliable, low bleed performance.
• Innovative Alumaseal™ and Integra-Gap™ technology; choose Restek for leak-proof retention gap options.
Figure 1
The Alumaseal™ connector
The Alumaseal™ connector is the best column connector for coupling fused silica and metal
columns, even columns of different internal diameters. Made of aluminum, it is designed for
high temperature performance. These connectors have been factory-coupled and tested using
temperature programmed mass spectrometry and have shown no signs of leaks, even at 430°C.
The Alumaseal™ connector offers:
•A leak-tight connection.
•Low dead volume.
•Low thermal mass.
•High inertness.