Analytical Instrumentation Analyte Naphthalene R2 0.998
1-Methylnaphthalene 0.998 2-Methylnaphthalene 0.997 Acenaphthylene Acenaphthene Fluorene
Phenanthrene Anthracene Fluoranthene Pyrene
Benz[a]anthracene Chrysene
0.999 0.998 0.998 0.998 0.999 1.000 1.000 0.998 0.999
Benzo[b]fluoranthene 0.996 Benzo[k]fluoranthene 0.996 Benzo[a]pyrene
0.998
Indeno[1,2,3-cd]pyrene 0.998 Benzo[ghi]perylene
0.998
Figure 3: Calibration curve for fluoranthene standard above shows linearity from 5 to 2500 ppb, with R2
=0.999.
As shown in Figure 4, the Used Oil (S) showed the highest levels of any quantitated PAH, with significantly higher levels of the smaller PAHs, naphthalene and methylnaphthalenes. Especially interesting was the fact that even after an oil change, engine oil from the car routinely driven short distances still showed significantly higher levels of these smaller PAHs than the used oils from other cars.
In addition to the quantified target components, alkylated PAHs, which may have higher environmental toxicity, were found in the used motor oils. Based on characteristic masses and position in the structured, two-dimensional chromatogram, various C0- C3-phenanthrene isomers were identified. In Figure 5 below, representative masses for C0-C3 clusters of phenanthrene isomers calculated from the chemical formula are plotted in the chromatographic contour plots. Two additional significant figures beyond the decimal available on the Pegasus BT 4D provide extra specificity. The deconvoluted Peak True spectra corresponding to the most intense peak of each cluster are compared to spectra from commercial libraries for tentative identification.
Besides the ability to separate the PAHs from hydrocarbon interferences, the second dimension in GCxGC allows for better deconvolution results due to enhanced chromatographic resolution of peaks. An example of this is shown in Figure 6 below, where two peaks clearly separated in the 2nd dimension had co-eluted in the first dimension, causing an incorrect analyte assignment in the 1D run. In the peak shown in the 1D chromatogram, the deconvoluted Peak True spectrum contains m/z 57.11 and m/z 141.10 as major features and yields a low library similarity score of 777/1000. Further investigation with GCxGC analysis yields two separate, chromatographically-resolved peaks in the same 1st dimension retention time, which can be identified as nonadecane with the characteristic m/z 57.11 and 2,6-dimethylnaphthalene with m/z 141.10. Their respective library similarity scores are 869/1000 and 884/1000.
With the combination of improved chromatographic resolution and extra mass precision beyond the decimal, identifying compounds with heteroatomic substitutions with more specificity is also possible using Peak Find with NonTarget deconvolution.
Table 2: PAH Standard Calibration Linearity
Figure 4: Summary of PAH and alkyl PAH levels found in engine oil sample, reported in ppm, as determined by the Pegasus BT 4D.
5
Figure 5: C0-C3-phenanthrene isomer clusters shown with corresponding library-matched spectra for the largest peak in each cluster.
In Figure 7 below, examples of a sulfur-containing and an oxygen- containing analyte are shown, with excellent library similarity scores: benzo(b)thiophene and 1,2,3,4-tetrahydro-4-methyl-4-phenanthrol.
Conclusion
In this article, calibration curves were built for a standard set of PAHs and applied to engine oil samples with various levels of PAHs and alkylated PAHs. Following expectations for combustion efficiencies, larger levels of each PAH correlated with engines driven shorter distances routinely. With mass accuracies better than traditional nominal mass instruments the Pegasus BT 4D provided the ability to accurately quantitate targeted, regulated
compounds, as well as identify other components of interest by separating them in the 2nd dimension of GCxGC from the complex matrix of used engine oil.
Author Contact Details Christina Kelly, Sep. Sci. Applications Chemist LECO Corporation • Address: 3000 Lakeview Ave, Saint Joseph, MI 49085 • Tel: 269-985-5806 • Email:
christina_kelly@leco.com
Figure 6: The deconvolution example shown here compares the results of 1D vs. GCxGC analysis.
Figure 7: Nontargeted compounds containing oxygen and sulfur were identified in used engine oil.
OCTOBER / NOVEMBER •
WWW.PETRO-ONLINE.COM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
