12 May / June 2019
Table 4: Average observed volume % values for dimethoxymethane, n-methylaniline, and 2,5-dimethylfuran at spikes of 20%, 10%, 5%, 2%, 1%, 0.5%, 0.2%, 0.1%, and 0.05% v/v. Even over a very extended concentration range, each compound demonstrated a high degree of linearity.
Compound
Dimethoxymethane N-Methylaniline 2,5-Dimethylfuran
Compound
Dimethoxymethane N-Methylaniline 2,5-Dimethylfuran
20% Spike 20.9 22.8 20.7
0.5% Spike 0.49 0.54 0.47
10% Spike 9.85 11.2 9.96
0.2% Spike 0.22 0.22 0.16
these conditions, it was quantified over the 1% - 10% v/v linear range with an R2
value of 0.998. An example of spectral deconvolution can
be seen in Figure 2. The spectral differences between acetone and isopentane allowed them to be distinguished and characterised separately despite their similar retention indices.
4. Conclusions
GC-VUV is able to successfully analyse and quantify several NTGAs in a 34-minute run time. These NTGAs can be uniquely identified by their spectral fingerprints, and spectral deconvolution allows these compounds to be identified and quantified even if they coelute with other compounds in gasoline. Highly linear data can be obtained for each NTGA over a wide range of concentrations without sacrificing the PIONA and oxygenate analysis necessary for fuel stream monitoring and regulation. Additionally, the ability to analyse these compounds
5% Spike 4.90 5.62 4.88
0.1% Spike 0.09 0.07 0.06
2% Spike 1.83 2.20 1.83
0.05% Spike 0.06 0.03 0.02
1% Spike 1.00 1.11 1.01
R2
0.999 0.999 0.999
without changing the hardware configuration or method parameters greatly simplifies the analysis, making it a desirable alternative to cumbersome methods such as ASTM D6730 or ASTM D6839.
Despite its advantages, NTGA analysis with GC-VUV is limited in part by the VUV spectral library. Unlike mass spectral libraries such as the one from NIST, which have been built over multiple decades, the VUV spectral library is relatively small. It contains entries for a large number of gasoline compounds and is continually growing, but many NTGAs may not exist in the library. If data is not available, unknown NTGA peaks may need to be identified with another technique, such as GC- MS. Once identified, a reference standard of the compound must be purchased and analysed so it can be included in the spectral library. However, once the compound is in the library, it can be analysed and quantified using GC-VUV as described in this paper.
5. References:
1. M. Amine, M.A.H. Zahran, E.N. Awad, S.M.El-Zein, Y. Barakat. International Journal of Modern Organic Chemistry 2(3) (2013) 226-250.
2. United States Environmental Protection Agency. Gasoline Reid Vapor Pressure (2018).
https://www.epa.gov/gasoline-standards gasoline-reid-vapor-pressure#information.
3. United States Environmental Protection Agency. Final Rule for Model Year 2017 and Later Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards (2018).
https://www.epa.gov/regulations-emissions-vehicles-and-engines final-rule-model-year-2017-and-later-light-duty-vehicle
4. Renewable Fuels Association. E15 Retailer Handbook (2013). Figure 2a
Figure 2b
Figure 2c
Figure 2. a) Sample chromatogram of oxygenate-free gasoline containing 1% acetone v/v. Acetone and isopentane coelution is marked. b) Coelution of acetone and isopent- ane. Without spectral deconvolution, the acetone peak may have gone unnoticed under the isopentane peak; however, VUV can distinguish each compound and quantify them accurately. c) Observed spectrum at the coelution of acetone and isopentane. The observed spectrum has spectral features of both acetone and isopentane, and both com- pounds can be identified using VUV. d) Despite coeluting with isopentane, acetone can be quantified over the 1% - 10% v/v range with a high degree of linearity.
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