tion in high-temperature analysis. They combined
the unique properties of Siltek
™
deactivation, high-
temperature fused silica tubing, and a specially syn-
thesized dimethyl polysiloxane phase to create a
non-polar capillary columnwith thermal stability
up to 380°C. The result is the new Stx
®
-1HT col-
umn, which shows significant low bleed, even at
temperatures above 340°C (Figure 1).
Total petroleum hydrocarbon (TPH) analysis is a
common test performed in environmental laborato-
ries. In addition to gasoline range and diesel range
organics (GRO andDRO, respectively), samples
often contain highmolecular weight hydrocarbons
frommotor oil or hydraulic fluid. To elute these
highmolecular weight hydrocarbons from the col-
umn requires high oven temperatures. The Stx
®
-1HT
column has the necessary thermal stability and low
bleed to perform the analysis of hydrocarbons up
to C58 in approximately 50minutes (Figure 2).
To ensure continued low-bleed performance at high
temperatures, it is critical to prevent oxygen from
entering the column. Therefore, the system should
be leak-checked before heating the column. Even a
small leakwill cause air to enter and bleed to
increase. Also, we recommend using graphite fer-
Innovators of High Resolution Chromatography Products
the
in this issue
Fast Analysis of Dioxin and Related
Compounds
…pg. 6
TO-Can
™
Air
Monitoring Canisters
…pg. 7
Column Bleed and System
Contamination
…pg. 8-9
HPLCAnalysis of Carboxylic Acids
…pg. 10
Analyzing Heat Levels of Spicy Foods
…pg. 11
Trident
™
Direct Guard Column System
…pg. 12
Analysis of PAHs
…pg. 13
Rtx
®
-OPPesticides 2 Columns
…pg. 14–15
US EPAMethod 8260BReference
Materials
…pg. 16
MESI—Membrane Extraction
Sorbent Interface
…pg. 17
Peak Performers
…pg. 18-19
Behind the Scenes
…pg. 16
800-356-1688
814-353-1300
Spring
’01
by Neil Mosesman, GCColumns Product MarketingManager,
&Dinesh Patwardhan, Ph.D., Senior R&DChemist
INTERNATIONAL
Stx
®
-1HTColumns
LowBleed for High-TemperatureAnalysis
Advantage
Stx
®
-1HT
High-Temp.
Column
…pg. 1–2
Restek
On-the-Road
…pg. 3
Separating
m-
and
p-
Xylene Isomers
…pg. 4
NewReference Texts
…pg. 5
Analyzing highmolecular weight compounds by gas
chromatography (GC) has been difficult because of
the limited thermal stability of the stationary phases
and the fused silica tubing. At temperatures above
340°Cmost stationary phases exhibit high bleed that
can interferewith peak identification and affect
quantitaion. In addition, the polyimide coating on
standard fused silica tubing
canbecome brittle at tem-
peratures above 360°C,
causing spontaneous
breakagewhen the column
is exposed to elevated tem-
peratures too long.
Extensive research by
Restek R&D scientists has
led to a significant innova-
✔
Thermally stable to 380°C
✔
True dimethyl polysiloxane
polarity
✔
Low bleed (<10pa@ 380°C)
✔
Unique Siltek
™
-deactivated
high-temperature tubing
Stx
™
-1HT
0min.
20
40
60
30m, 0.32mm ID, 0.10µmStx
™
-1HT
(cat.# 11709)
& 30m, 0.32mm ID,
0.10µmRtx
®
-1 (cat.# 10109);
GC:
Agilent 6890;
Oven program:
100°C
to 340°C at 10°C/min. (hold 10min.) to
360°C@ 10°C/min. (hold 10min.) to
380°C@ 10°C/min. (hold 10min.);
Detector:
FID@ 380°C;
Injector:
split
at 250°C;
Septum purge:
4.0cc/min.;
Carrier gas:
helium;
Split vent flow
rate:
25cc/min., 20:1 split;
Head pres-
sure:
8.0psi;
Linear velocity:
26cm/sec.;
Make-up gas flow:
45cc/min., nitrogen
Figure 1
The Stx
™
-1HT column exhibits extremely low bleed at high temperatures.
GC_EX00397,
GC_EX00396
new
50
0
10
20
30
40
picoamps
380°C
340°C 360°C
