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2007 vol. 3
Chemical/Petrochemical
Unsurpassed Stability
The high temperature programs required for
analysis of biodiesel oils (B100) by either ASTM
D-6584 or EN-14105 methodology present a sig-
nificant challenge to the analytical column. High-
temperature fused silica tubing breaks down under
these extreme conditions, but the metal MXT
®
tub-
ing does not degrade, even at temperatures up to
430°C (Figure 1). This allows analysts to bake out
any residue eluting after the triglycerides, prevent-
ing carryover without damaging the column.
So how well do the MXT
®
-Biodiesel TG columns
perform? We conducted a benchmarking experi-
ment comparing an MXT
®
-Biodiesel TG column
with Integra-Gap™ to a high-temperature fused
silica column coupled to a conventional 0.53mm
retention gap. Methodology followed ASTM
method D-6584, except the final temperature was
modified to 430°C. Both columns were subjected
to 100 temperature cycles up to 430°C and deriva-
tized B100 was injected.
This evaluation was performed using a Shimadzu
2010 gas chromatograph equipped with a flame
ionization detector, a model AOC 20i + S autosam-
pler with a 10µL SGE syringe and 42mm 26-gauge
needle, and a cold on-column programmable
injector with a stainless steel injector insert. A
Parker hydrogen generator supplied the carrier
gas. Peak symmetry and retention time were eval-
uated as indicators of thermal stability.
Peak symmetry of butanetriol on a commercial
high-temperature fused silica column deteriorates
after just 20 injections, compared to the excellent
symmetry that is maintained on the MXT
®
-
Biodiesel TG column (Figure 2). In addition to peak
shape, retention time stability was used to evaluate
column performance. The decrease in retention
time seen on the high-temperature fused silica col-
umn indicates the liquid phase is being lost
(Figure 3). In contrast, the consistent retention
times obtained on the MXT
®
-Biodiesel TG column
demonstrate its stability. Practically, this translates
into reliable performance and longer column life-
times.
Analytical Alternatives
Factory connected 0.32mm MXT
®
-Biodiesel TG
columns & 0.53mm retention gaps
For accurate analysis of heavy triglycerides, on-col-
umn injection is required. ASTMD-6584 describes
the use of a 0.32mm analytical column coupled
with a 0.53mm retention gap. The 0.53mm ID
retention gap allows the cool on-column technique
to be used, but care must be taken to minimize
dead volume and to establish a leak-tight connection.
Restek’s 0.32mm MXT
®
-Biodiesel TG columns are
factory-coupled to a 0.53mm MXT
®
retention gap
with an Alumaseal™ connector, ensuring a leak-
Figure 1
MXT
®
-Biodiesel TG columns are undamaged by high ther-
mal cycles compared to high-temperature fused silica columns
which breakdown under the same conditions.
100 temperature cycles to 430°C totaling 500 minutes at maximum temperature.
Figure 2
Stable and consistent peak shape for the internal standard
butanetriol gives you more accurate quantitation.
Figure 3
Retention time is stable on a metal MXT
®
-Biodiesel TG
column, even after 100 cycles up to 430°C.
0.8
1
1.2
1.4
1.6
1.8
2
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 100
Number of Injections
Asymmetry value
HT Fused Silica
MXT-Biodiesel TG
18.00
18.20
18.40
18.60
18.80
19.00
19.20
19.40
19.60
19.80
20.00
1 9 17 25 33 41 49 57 65 73 81 89 97 100
Number of Injections
MXT-Biodiesel TG
HT Fused Silica
Tricaprin RT
MXT
®
-Biodiesel TG
columns are
undamaged by
high thermal
cycles.
HT fused silica
columns, labeled
as stable to 430°C,
show pitting and
breakdown.
More stable than
fused silica!