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• 8 • 800-356-1688 • 2004 vol. 3
Gasolines are complex mixtures of hundreds of
compounds. Information about concentrations
of the individual components is important for
evaluating raw materials and controlling refin-
ery processes. A high-resolution GC method for
detailed hydrocarbon analysis (DHA) of gaso-
lines is outlined in American Society of Testing
and Materials (ASTM) Method D-6730-01—often
referred to as the PONA (paraffins, olefins,
naphthenes, aromatics) or PIANO (paraffins,
isoparaffins, aromatics, naphthenes, olefins)
analysis.* ASTM D-6730-01 is specific for the
analysis of these hydrocarbon components, plus
oxygenated additives such as methanol, ethanol,
tert-butanol, methyl tert-butyl ether (MTBE), and
tert-amyl methyl ether (TAME) in spark-ignition
engine fuels.
To maximize resolution of these complex mix-
tures, the ASTM method recommends a 100-
meter x 0.25mm ID capillary column coated with
0.5µm of 100% dimethyl polysiloxane stationary
phase, and sets minimum 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 2-3 meters long, coated with 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 column meets all ASTM D-6730-
01 requirements for critical pair resolution, as
demonstrated by Figure 2. A 2.6-meter tuning
column was 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 ASTM D-6730-01
analysis, Rtx®-1PONA columns meet the similar-
ly stringent requirements of Canadian General
Standards Board (CGSB) methodology. For addi-
tional detailed hydrocarbon analysis chro-
matograms and more 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.
Improving Detailed Hydrocarbon Analysis
Using an Rtx® -1PONA Capillary GC Column
•Column meets or exceeds all ASTM D-6730-01 and Canadian General Standards Board
method requirements.
• 30% faster analysis (C13 retention = 97 minutes), 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, Petroleum Applications Chemist,
and Neil Mosesman, GC Columns Product Marketing Manager
Rtx®-1 PONA Column (fused silica)
(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
Figure 1 Sharp, symmetric peak for ethanol (gasoline oxygenate), using an Rtx®-1PONA column.
1
2
3
4
9 10 11 12 min.
*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®-5 PONA Tuning Column
(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 column ODs from 0.33–0.74mm (Restek
0.1mm–0.53mm ID).
• Angled connector reduces strain on connection.
Description 5-pk./price
Universal Press-Tight®
Connectors 20400 $38
Siltek™-treated Universal
Press-Tight® Connectors 20480 $48
Universal Angled Press-Tight®
Connectors 20446 $45
Siltek™-treated Universal
Angled Press-Tight® Connectors 20482 $65
Vu2 Union™ Connector
A Vu2 Union™ connector combines the simplicity of
a Press-Tight® union with the strength of a metal
union. The columns cannot unexpectedly discon-
nect, even at temperatures as high as 400°C.
Kits include: Vu2 Union™ 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
Vu2 Union™ Connector Kit
(0.15–0.25mm) 21105 $128
Vu2 Union™ Connector Kit
(0.28/0.32mm) 21106 $128
Vu2 Union™ Connector Kit
(0.45/0.50 & 0.53mm) 21107 $128