Determination of Hydrocarbon Group Types in Spark Ignition Fuels
using Gas Chromatography with Vacuum Ultraviolet Absorption
Spectroscopy (GC-VUV)
Application Note
INTRODUCTION
The VUV detector is the next generation GC detector for
PIONA analysis; simplifying the complex analysis of
hydrocarbon samples with short analysis times, including
spark ignition fuels. There are many challenges within the
petrochemical industry and associated GC analysis
methods. As regulations continuously drive down the
accepted levels of impurities in gasolines, lower detection
and quantification levels must be observed when using GC
as a method for analysis. Fuel impurities must be removed
whilst also retaining and characterising paraffins, iso-
paraffins, olefins, napthenes and aromatics (PIONA) as well
as other hydrocarbon classes to maintain the octane value
of the system.
ASTM D6730 is the standard test method for the
determination of individual components in spark ignition
fuels using GC-FID. However, this detailed hydrocarbon
analysis (DHA) is time consuming with long analyses,
column tuning and extensive post processing times. DHA is
reliant on reproducible retention index values; requiring
optimal controlled operating, flow and temperature
conditions,
for
identification
and
quantification.
Additionally, full gasoline analysis can be completed using
multi-dimensional gas chromatography; a highly complex
column switching technique to determine carbon number
distribution for the different component classes. Due to
the sophisticated setup of the multi-dimensional GC;
which contains numerous valves, columns and traps, this
analysis is expensive and challenging to use.
VUV Analytics have developed a benchtop vacuum
ultraviolet (VUV) spectrometer that utilises an ultraviolet
spectrum (stored library), retention indices and relative
response factors to provide excellent sensitivity and
unparalleled selectivity for the analysis of spark ignition
fuels, when coupled to a GC. The VUV PIONA+ analyser is
preconfigured for the determination of bulk PIONA,
specific oxygenates and BTEX (benzene, toluene, ethyl
benzene and xylenes) compound content, in a single
measurement. In addition, ASTM D8071 is the standard
method for the determination of hydrocarbon group types
using GC-VUV.
This application note details the analysis of a reference
standards along with gasoline, alkylate, reformate and
racing fuel samples on the SCION 436 GC with VUV
detector according to the ASTM D8071 method.
EXPERIMENTAL
The SCION 436 GC equipped with a 8400 autosampler, S/SL
injector and VUV detector was used for the analysis of
alkylate, gasoline and a racing fuel sample. Reference
standards included a PIONA+ mix and a ASTM P-00800
reference and performance check. Repeatability of the
system was completed using a Supelco reformate sample.
System suitability was also tested using a benzene
standard, in order to calculate the benzene response.
Table 1 details the analytical parameters with Figure 1
showing the analytical instrumentation, used throughout
this application.
Conditions
S/SL
250°C, 0.3µL, split 20:1
Column
30m x 0.25mm x 0.25µm
Oven Programme
35°C (hold 10 min), 7°C/min to 200°C
Carrier Gas
Helium 1mL/min constant
Detector Flow Tube
275°C
Transfer Tube
275°C
Wavelength
125-240nm
Table 1. Analytical conditions of the GC-VUV
Fig 1. SCION 436 GC with VUV detector
AN0021
Fig 3. Separation of PIONA calibration standard
RESULTS
The retention indices (RI) and relative response
factors (RRF) of all hydrocarbon classes and individual
compounds are used during data processing. RRF of
the classes and compounds are prep-programmed in
the VUV Analyze software.
The VUV detector scans during the GC analysis at a
frequency of over 90Hz. The PIONA+ analyser
eliminates the issue of complex chromatographic
separation as the VUV Analyze software automatically
deconvolves overlapping spectral responses. The VUV
absorbance spectra is specific to the compound
chemical structure. The VUV software is not
dependent on very precise retention time. The built in
UV spectral library was used to confirm correct peak
identification. Additionally, spectral filters can be used
as a visualisation tool to assist in discriminating
between different compound classes. The spectral
filters are applied post data acquisition to enhance
analyte sensitivity.
Baseline resolution is not vital using the PIONA+ as
the specific UV spectra still accurately identifies and
quantifies compounds.
Figures 2-6 show the chromatograms of the ASTM
P-00800
reference
standard,
PIONA
reference
standard, gasoline sample, alkylate sample and racing
fuel sample, respectively.
Fig 4. Separation of Alkylate sample
Fig 5. Separation of Gasoline sample
Fig 2. Separation of ASTM D8071 calibration standard
Fig 6. Separation of Racing Fuel sample
Data processing is an automated process through the
VUV Analyze software. The PIONA+ analyser divides the
total chromatogram time region into individual time
slices. Each time slice is then used to calculate the total
absorbance. Both mass% and volume% are calculated
from the total response contribution of Figures 7-9
detail the comparison of the expected values and actual
values of the ASTM P-00800 calibration standard and
the PIONA standard results when analysed via the GC-
VUV.
The actual and expected results gave comparable
results, for both ASTM P-00800 and PIONA standards,
highlighting the accuracy of the VUV system.
Table 2 details a typical PIONA report generated by the
VUV Analyze software. The hydrocarbon class values, as
well as a selection of individual compounds obtained
when a gasoline sample was analysed via GC-VUV, is
shown.
P
I
O
N
A
C4
1.70
1.92
0.32
C5
2.86
22.31
1.21
0.45
C6
1.14
6.05
0.61
1.92
0.92
C7
1.00
3.85
0.78
0.54
11.54
C8
0.26
1.81
0.11
0.73
13.00
C9
0.08
0.47
0.05
7.85
C10
0.02
0.11
0.03
0.07
2.17
C11
0.01
0.01
0.15
C12
0.09
C13
C14
Total
7.07
36.52
3.07
3.76
35.72
ETBE
9.15
Ethanol
4.16
Xylenes
9.73
Table 2. Composition of a gasoline sample (mass%)
The Supelco reformate sample was analysed in five
consecutive injections in order to determine the
repeatability of the system. Table 3 details the
repeatability values as well as the reference values
stated in method D8071. The repeatability of benzene,
the system suitability sample is also detailed, however,
no D8071 reference is specified.
The values in Table 3 show excellent repeatability
of
the
GC-VUV
system,
well
within
the
specifications set in ASTM D8071. The excellent
repeatability of benzene shows that the system
was suitable for subsequent analyses.
Mass %
SD
D8071 Ref
P
6.71
0.03
0.05-0.14
I
22.33
0.05
0.14-0.34
O
0.38
0.03
0.06-0.26
N
1.13
0.05
0.16
A
75.66
0.10
0.06-0.15
Benzene
6.08
0.01
Table 5. Repeatability of reformate sample (n=5)
Fig 7. Expected and actual values of hydrocarbon groups ASTM standard (mass%)
Fig 8. Expected and actual values of individual components ASTM standard (mass%)
Fig 9. Expected and actual values of hydrocarbon groups PIONA standard (mass%)
CONCLUSION
The SCION GC with VUV detector offers the ideal
solution for eliminating typical time consuming and
difficult methods, when analysing spark ignition fuels
for the determination of hydrocarbon classes and
individual compounds. The PIONA+ analyser offers
PIONA compound class characterisation in a single
measurement whilst being operated to ASTM D8071
standards. Easy analysis of complex
samples
combined with automated data processing and
confirmation via a spectral library, ensures a reliable
performance with reproducible results in under 35
minutes.
SCION Instruments HQ
SCION Instruments NL BV
Livingston Business Centre,
4462, Goes,
Kirkton Road South, Livingston,
Stanleyweg 4.
EH54 7FA, Scotland, UK.
The Netherlands
Tel: +44 1506 300 200
Tel: +31 113 348 926
www.scioninstruments.com
www.scioninstruments.com
