Lynen, Frederic

Van de Velde, Thomas

Ghent University Academic Bibliography

Fingerprinting bitumen from archaeological sites using 2-Dimensional Flow-Modulated Gas ChromatographyThomas Van de Velde1, Frederic Lynen11Separation Science Group, Department of Organic and Macromolecular Chemistry, Ghent University, Krijgslaan 281 (S4), 9000 Ghent, BelgiumINTRODUCTIONREFERENCESCONCLUSION• Comprehensive flow-modulated two-dimensional GC has shown to bea useful tool for biomarker targeting in archaeological bitumen.• The setup is quite straightforward and easy to operate.• The parallel operation of an FID and Quadropole MSD offers flexibilityin data processing and makes compound identification possible.• The analysis on the samples used in this test-case makes clear thatboth archaeological sites were supplied with bitumen from at least twodifferent source areas.REFERENCES2-DIMENSIONAL GC IN BITUMEN RESEARCH1. Eiserbeck C., Nelson R.K., Grice K., Curiale J., Reddy C.M. & Raiteri P. 2011. Separation of 18α(H)-,18β(H)-oleanane and lupane by comprehensive two- dimensional gas chromatography. Journal ofChromatography A 1218: 5549-5553.2. Misselwitz M., Cochran J., English C. & Burger B. Fingerprinting Crude Oils and Tarballs Using Biomarkersand Comprehensive Two-Dimensional Gas Chromatography [Online].http://www.restek.com/Technical-Resources/Technical-Library/Environmental/petro_PCAN1789-UNV.[Accessed April 18 2017].3. Dallüge J., Beens J. & Brinkman U.a.T. 2003. Comprehensive two-dimensional gas chromatography: apowerful and versatile analytical tool. Journal of Chromatography 1000: 69-108.Biomarker analysis by means of GC-MS has been the standard for years in oil-spill analysis,sourcing unknown hydrocarbons, and in environmental assessments. The techniques developed forthis practice, however, do not limit themselves to present-day issues: the same analyticaltechniques have proven to be very useful to acquire archaeological and historical knowledge.Bitumen, currently mainly a by-product of petroleum exploration and –drilling, has been used bymankind extensively for over six thousand years. It was commonly used to either glue- orwaterproofing items, ranging from the smallest type of objects such as jewellery, to ships andmonumental architecture.Two-dimensional comprehensive Gas Chromatography is more and more becoming embedded inpetro-chemistry for the detailed analysis of biomarkers1,2. Its main advantages over the moretraditional one-dimensional GC include:• potential for higher peak capacity,• easier compound separation from matrix interferences,• signal enhancement due to analyte refocusing on the modulator3.However, this is generally achieved by employing cryogenic modulation and time-of-flight massspectrometry (TOF MS). Analyses using these techniques are relatively complex and costly tooperate. We are here presenting an experimental setup using a Forward fill/flush flow-modulatedsystem with FID and Quadrupole MS detector in parallel.GC InstrumentationAgilent 7890A GC-systemInjection Splitless injection                  4µL in iso-octaneInjector temperature 280°CTemperature GradientInitial T.Ramp 1Ramp 250°C hold 2 minutes10°C/min to 160°Chold 4 min.4°C/min. to 300°CHold 20 min.Modulation parametersModulation delay:Sample time:Modulation period0,02 minutes1,899 seconds2,0 secondsDimension 1 Dimension 2Columns Agilent HP5-MS30m 0,25mm 0,25µmAgilent DB17-MS3m 0,18mm 0,18µmFlow rates 0,6 ml/minHydrogen carrier gas25 ml/minHydrogen carrier gasDetector Agilent 5975C MSDMin50 cm x 0,10 mmDeactivated Fused Silica tubing120 cm x 0,25 mmDeactivated Fused Silica tubingHP-5MSDB-17MSInjector FIDMSDFlow Modulator Glass Y-splitter (1:12 split)For this research, a combination of a 30m HP-5MS and 2m DB-17MS column was used. A glass Y-splitter and deactivated fused silica tubing was used to achieve a 1:12 split (MSD:FID) prior todetection (see Figure 3). This was necessary due to the high flow rate of the second dimension(25mL/min), which would be problematic when introduced directly into the MSD.Employing one-dimensional GC, generally m/z 191 is targeted for specific compound identificationrather than the total ion chromatogram (Figure 4A). The FID data provided by our setup presentswell-separated peaks and the ability to easily determine molecular ratios, both with MSD and FID.The additional MSD data can be used to identify individual compounds based on their mass specs.However, this setup has one major disadvantage; small trace compounds visible in the FID datacould often not be identified in the MSD data. This is the result of the split introduced right after thesecond column. To resolve this issue, possible solutions included more concentrated samples, ahigher injection volume, or the usage of cryogenic modulation.Figure 3: Schematized version of the experimental setup and all relevant parameters.Figure 1: Several examples of artefacts where bitumen was used. Bitumen used as a sculpting material to fabricate jar stoppers are a commonly found item on archaeological sites (left image, ca. 1900 B.C.). The Standard of Ur (right image,ca. 2500 B.C.) was excavated from the Royal Cemeteries and consists of a wooden core to which shell and lapis lazulielements were glued with bitumen.Figure 5: chromatogram of an archaeological bitumen samples  analysed by the experimental setup. Hopanes and steranes are clearly separated. The highlighted compounds are, amongst others, commonly used for fingerprinting. (1) 18α(H)-22,29,30-trisnorneohopane (Ts), (2) 17α(H)-22,29,30)trisnorhopane (Tm), (3) 17α(H), 21β(H)-30-norhopane, (4) oleanane, (5) 17α(H), 21β(H)-hopane , (6) 17β(H), 21α(H)-hopane (moretane), (7) 17α(H), 21β(H), 22(S)-homohopane &17α(H), 21β(H), 22(R)-homohopane (8) Gammacerane. Bitumen surfaces naturally at specific locations (o.a. in southwest Iran and in Iraq) where it could beeasily collected. Already in the Palaeolithic period there is (rare) evidence of the usage of bitumenby mankind’s ancestors. However, it is from around 5000 B.C. onwards that the material becomesexploited on large scale and shipped over long-distance and overseas. By analysing bitumen foundon archaeological sites and determining where it originated, archaeologists obtain valuableknowledge on trade networks and interregional contacts. This holds especially true for bitumen, asthere was an extensive trade in this specific product which can be labelled as a true industry.SOURCING ARCHAEOLOGICAL BITUMENFigure 2: Map of the Near East  highlighting the areas were major bitumen extraction occurred in Antiquity.These areas are:1. The Mosul Area (Iraq)2. The Hit Area (Iraq)3. The Deh Luran Plain (Iran)4. Susiana Plain (Iran)Almost all bitumen excavated fromArchaeological sites in the Near East can beTraced back to one (or several) of theseareas.00,20,40,60,811,21,41,61,8Molecular ratio's (FID)Failaka Tell Abraq 1 Tell Abraq 2 Tell Abraq 3 Tell Abraq 4Five archaeological samples originating from two different archaeological sites were selected toinvestigate the potential of flow-modulated comprehensive GC for sourcing ancient bitumen. Bothsites are located in the Persian Gulf (see Figure 2):• F6 on Failaka Island (Kuwait)• Tell Abraq in the Sharjah Emirate (U.A.E.)Bitumen was found in considerable quantities on both sites, despite the absence of nearbyseepages, indicating import.ARCHAEOLOGICAL SAMPLES1234Figure 4: (A)Traditional GC-MS chromatogram (m/z 191) of an archaeological bitumen sample. Figure 4B exhibits several molecular ratios commonly used in biomarker analysis. It is immediately evident that only the sample from F6 Failaka shows the presence of the chemical compound Oleanane, which is indicative of oils coming from the Tertiary Padbeh Source Rock formation (in case of this geographical area). Molecular ratios support this hypothesis, o.a. with a significant higher 29ab/30ab ratio than any other sample. The ratios in figure 4B are: • Ts/Tm: 18α(H)-22,29,30-trisnorneohopane / 17α(H)-22,29,30-trisnorhopane• 29ab/30ab: 17α(H), 21β(H)-30-norhopane / 17α(H), 21β(H)-hopane• 30ba/30ab: 17β(H), 21α(H)-hopane (moretane) / 17α(H), 21β(H)-hopane• 31abS/31abR: 17α(H), 21β(H), 22(S)-homohopane / 17α(H), 21β(H), 22(R)-homohopaneFigure 4C shows the structures of the compounds 17α(H), 21β(H)-hopane (C1), 18α(H)-22,29,30-trisnorneohopane (C2), and 17α(H)-22,29,30-trisnorhopane (C3)BSETUP12305000010000015000020000025000045 46 47 48 49 50 51 52 53TsTm29ab30abGCRN31abS/ROLNm/z 19130baA C

Fingerprinting bitumen from archaeological sites using 2-dimensional flow-modulated gas chromatography

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Fingerprinting bitumen from archaeological sites using 2-dimensional flow-modulated gas chromatography

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