• 8 •
800-356-1688 •
2004vol. 3
Gasolines are complexmixtures of hundreds of
compounds. Information about concentrations
of the individual components is important for
evaluating rawmaterials and controlling refin-
ery processes. A high-resolutionGCmethod for
detailed hydrocarbon analysis (DHA) of gaso-
lines is outlined in American Society ofTesting
andMaterials (ASTM) MethodD-6730-01—often
referred to as the PONA (paraffins, olefins,
naphthenes, aromatics) or PIANO (paraffins,
isoparaffins, aromatics, naphthenes, olefins)
analysis.*ASTMD-6730-01 is specific for the
analysis of these hydrocarbon components, plus
oxygenated additives such asmethanol, ethanol,
tert
-butanol, methyl
tert
-butyl ether (MTBE), and
tert
-amyl methyl ether (TAME) in spark-ignition
engine fuels.
Tomaximize resolution of these complexmix-
tures, the ASTMmethod recommends a 100-
meter x 0.25mm ID capillary column coatedwith
0.5µm of 100% dimethyl polysiloxane stationary
phase, and setsminimum resolution criteria for
several critical pairs of closely eluting com-
pounds.To retain the aromatics, and accomplish
the separations, a short tuning column, approxi-
mately 2-3meters long, coatedwith 5%
diphenyl/95% dimethyl polysiloxane polymer, is
connected to the inlet of the 100-meter analyti-
cal column.Through a series of trial analyses,
the length of the tuning column is adjusted to
ensure the critical resolutions are achieved.
Analytical columns used for this application
must exhibit high efficiency and exceptional
inertness, especially for polar oxygenates in
gasoline. Figure 1 illustrates a column efficiency
of 613,596 total theoretical plates, measured on
C5, and shows excellent peak symmetry for the
oxygenated additives, including ethanol and
t-
butanol (
t-
butanol skewness= 1.25).We test
every Rtx
®
-1PONA column for retention (k), effi-
ciency (n), stationary phase selectivity (RI), and
bleed, and guarantee reproducible column-to-
column performance.
An Rtx
®
-1PONA columnmeets all ASTMD-6730-
01 requirements for critical pair resolution, as
demonstrated by Figure 2. A 2.6-meter tuning
columnwas used to achieve the highlighted
resolutions, based on retention of the aromatics
(e.g., resolution for 1-methylcyclopentene /
benzene= 1.28.).
In addition to qualifying for the ASTMD-6730-01
analysis, Rtx
®
-1PONA columnsmeet the similar-
ly stringent requirements of CanadianGeneral
Standards Board (CGSB) methodology. For addi-
tional detailed hydrocarbon analysis chro-
matograms andmore information about these
high-performance columns, please request a
free copy of Applications Note 59568, or review
the applications note and chromatography on
our website.
ImprovingDetailedHydrocarbonAnalysis
Using an Rtx
®
-1PONA Capillary GCColumn
•Columnmeets or exceeds all ASTMD-6730-01 and CanadianGeneral Standards Board
method requirements.
•30% faster analysis (C13 retention= 97minutes), using helium.
•Excellent responses and peak symmetry for polar oxygenates.
•Guaranteed column-to-column reproducibility for retention, efficiency, selectivity, peak
skewness, resolution, low bleed.
by Barry Burger, PetroleumApplications Chemist,
andNeil Mosesman, GCColumns ProductMarketingManager
Rtx
®
-1PONAColumn (fusedsilica)
(Crossbond
®
100% dimethyl polysiloxane phase optimized
for hydrocarbon analysis) (temp. limits.: -60 to 300/340°C)
100m, 0.25mm ID, 0.50µm df, cat.# 10195,
$795
Figure1
Sharp, symmetricpeak for ethanol (gasolineoxygenate), usinganRtx®-1PONA column.
1
2
3
4
9
10
11
12min.
*In alternate terminology: paraffins & isoparaffins= alkanes; naphthenes= cyclic alkanes; olefins= alkenes.
Rtx
®
-1PONA, 100m, 0.25mm ID, 0.5µm (cat.# 10195)
w/ Rtx
®
-5 tuning column, 2.62m, 0.25mm ID, 1.0µm,
connected via Press-Tight
®
connector (cat.# 20446)
Sample:
custom detailed hydrocarbons analysis
(DHA) mix, neat
Inj.:
0.01µL, split (split ratio 150:1),
4mm cup inlet liner (cat.# 20709)
Inj. temp.:
200ºC
Carrier gas:
helium, constant flow
Linear velocity: 28cm/sec. (2.3mL/min.)
Oven temp.:
35ºC
Det.:
FID@ 250ºC
1. ethanol
2. C5
3.
t-
butanol
4. 2-methylbutene-2
C5 efficiency: 613,596 total theoretical plates
k' (C5): 0.489
t-
butanol skewness: 1.25
Resolution (
t-
butanol/2-methylbutene-2): 5.60
Rtx®-5PONATuningColumn
(
Crossbond
®
5% diphenyl/95% dimethyl polysiloxane phase)
5m, 0.25mm ID, 1.0µm df, cat.# 554206,
$75
Press-Tight®Connectors
•Made from inert fused silica.
•Fit columnODs from 0.33–0.74mm (Restek
0.1mm–0.53mm ID).
•Angled connector reduces strainon connection.
Description
5-pk.
/price
Universal Press-Tight
®
Connectors
20400
$38
Siltek
™
-treatedUniversal
Press-Tight
®
Connectors
20480
$48
Universal Angled Press-Tight
®
Connectors
20446
$45
Siltek
™
-treatedUniversal
Angled Press-Tight
®
Connectors 20482
$65
Vu2Union™Connector
AVu2Union
™
connector combines the simplicity of
aPress-Tight
®
unionwith the strength of ametal
union.The columns cannot unexpectedly discon-
nect, even at temperatures as high as 400°C.
Kits include: Vu2Union
™
body, 2 knurled nuts,
2 Press-Tight
®
unions, and 4 ferrules
Secure, reliable
column-to-column
connections!
Connector Kit
(Ferrules Fit Restek Column ID)
cat.#
price
Vu2Union
™
Connector Kit
(0.15–0.25mm)
21105
$128
Vu2Union
™
Connector Kit
(0.28/0.32mm)
21106
$128
Vu2Union
™
Connector Kit
(0.45/0.50& 0.53mm)
21107
$128
