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Popescu Poli 5 12
  REV. CHIM. (Bucharest) ♦   63 ♦  No.5 ♦  2012 470 GC-MS Spectroscopy as Valuable Tool for the Study of Archaeological Ceramics POLIXENIA GEORGETA POPESCU 1,2* , CRISTIAN ENACHE-PREOTEASA  3 , FLORIN DINU BADEA  1 , EMANOIL PRIPON 4 ,MARIA MAGANU 5 1 University Politehnica of Bucharest, Faculty of Applied Chemistry and Material Science, 313 Splaiul Independenþei, 060042,Bucharest, Romania 2  Brukenthal National Museum, 4-5 Piaþa Mare, 550163, Sibiu, Romania 3   Central Phytosanitary Laboratory , 11 Voluntari Blv., 077190, Voluntari, Romania 4  Art and History County Museum, 9 Unirii Str., 450024, Zalãu, Romania 5 Romanian Academy, Organic Chemistry Center “Costin D. Neniþescu”, 202 B Splaiul Independenþei, 060023, Bucharest, Romania The identification of organic materials present in archeological findings by spectroscopic methods is important due to the information that can provide useful data both in archeological research and in the restoration and  preservation activities. Organic materials can be easily preserved on a ceramic support. This paper presentsanalytical results of microsamples taken from the surface of two neolithic ceramic fragments, found at the“Porþ Corãu” archaeological site. The fragments are decorated with a black colored layer, assumed to be natural bitumen due to the geographic area in which the fragments were excavated. The microsamples were characterized by means of gas chromatography coupled with mass spectrometry (GC-MS) and compared with reference samples. The analysis strategy being based on the detection of characteristic biomarkers. The results presented in this study were also supported by Fourier transform-infrared spectroscopy(FT-IR). Based on the analysis it can be concluded that the black layer is organic in nature, being a mixture of  birch bark tar with natural bitumen. This mixture is predominantly composed of birch bark tar. Keywords: GC-MS, birch bark tar, natural bitumen, Neolithic decorated ceramic In this paper we present the identification andcomposition analysis of the black material used ondecorated archeological ceramic objects found at “PorþCorãu” site. Preliminary research on the aforementionedceramic fragments was performed by means of by opticalmicroscopy and X ray diffraction, characterizing theceramic paste. Samples were collected from two ceramicfragments (C 137 and C 137 M) and subject to GC-MS andFT-IR spectroscopy.Located in the northwest of Romania, within the currentSãlaj and Bihor counties, the archaeological site at “PorþCorãu” is one of the most important Neo-Eneolithic sites inthis geographical area. The first systematic research herebegan in 1973 and continued until 1990. Due to the start of a construction project (dam reservoir) partially affectingthe site from “Porþ Corãu”, preventive research wasrequired for the investment approval. This research beganin 2002-2003 and was resumed in 2010 - 2011.The archeological research conducted in 2010 led tothe identification of levels of habituation belonging to theStarèevo – Criº culture, the Piºcolt culture, the so-calledSuplac group, the Coþofeni culture, the later bronze Hallstattculture, the Vekerzug Szentes culture and from the Romanperiod (second and third centuries A.D.). A possibledeepened dwelling (2.60 m x 2.60 m) was identified in theS5/2010 area. This residence, called Cx. 137, belongs tothe early Suplac housing level (4800-4500 B.C.) and exhibitsa rich ceramic inventory [1].Several fragments stand out among the discovereditems; these fragments belong to a large bowl with vertical,glossy black stripes, 2 to 2.3 cm wide. The archaeologicalmaterial obtained from the last two research campaignshas not yet been scientifically exploited or restored. Theblack colored layer is very well preserved and it is, by  * email: Tel.: +40 748 854082 macroscopic appearance, a bituminous substance. It is well known that a surface shale exploitation area waspresent in the immediate   geographical region from wherethe fragments were excavated. Furthermore, it is wellestablished from archaeological reports that black coloredlayer used for Neolithic ceramic decorations was oftennatural bitumen, obtained from shale. Birch bark tar wasalso used as black material, alone or mixed with naturalbitumen.Natural bitumen is found at surface level, as nativedeposits resulting from the seepage of crude petroleumthrough fissures or exposure by erosion, followed by evaporation of the more volatile components [2].Depending on the geological era and location, theassociated minerals and local water sources there aremany different bitumen compositions. Petroleum andbitumen composition determinations were and still remainan important topic, out gas chromatography coupled withmass spectrometry consistent results have been obtainedin this field [3]. Another useful characterization techniqueis represented by FT-IR spectroscopy which can provideefficient structural confirmation.In addition to the alkanes and cycloalkanes, there areseveral other classes of compounds which constituteimportant biological markers helpful in ‘fingerprinting’particular bitumen.Biological markers (biomarkers) are complex molecularcompounds once found in living organisms [4]. Biomarkersare very useful because they can provide information aboutthe entire petroleum or bitumen geology [5]. Due to theirgeneral resistance to weathering, biodegradation and otherpossible transformations, biomarkers are commonly employed as indicator of the contamination of petroleumas a result of its environment.  REV. CHIM. (Bucharest) ♦   63 ♦  No. 5 ♦  2012  471 It is of real importance to make the correct assignmentif all black paint or layer found on archaeological objectssrcinates from natural bitumen. Other sources of blacklayers could be from burnt natural resins [6]. Such resins,for example pine pitch or birch bark, contain a huge numberof cyclic or acyclic terpenoid hydrocarbons and derivatives[7, 8]. Experimental part  Materials Chloroform and hexane of spectroscopic purity wereused as received from Riedel and Merck, respectively, 60-230 mesh chromatography alumina was purchased fromFluka. Helium, purchased from Linde, was used as carriergas. Gravimetric measurements were performed on an AX 210 Mettler electronic balance. A Towson&Mercerultrasonic bath was used for samples dissolution. Syringeequipped with 0.2 μ m disposable cellulose filters werepurchased from Schleicher & Schuell.Gas chromatography was performed on a Trace GC Ultragas chromatograph fitted with an AS 2000 automaticinjector and a 10 μ L Hamilton syringe, equipped with a TR5 MS column of 30 m length, 0.25 mm diameter and 0.25 μ m film thickness from Thermo. Detection was performedon a Polaris Q ion trap mass spectrometer, all fitted modulesbeing provided by Thermo. Data was processed with thehelp of the Xcalibur software suite, version 1.3 and forspectral identification was performed by employing theNIST ‘02 library.  Procedure Reference samples of natural bitumen from thecollection of Organic Chemistry Technology Departmentfrom the Politehnica University of Bucharest, approximately 50 years old, were used. Reference samples of birch barktar from the collection of Brukenthal National Museum, were used.The reference sample (1000 mg) was dispersed intohexane by sonication for 10 min and subject to achromatographic filtration onto an open tubular column(30 mm diameter and 40 mm height) loaded with aluminaand using as solvent hexane. The hexane fraction wasconcentrated under vacuum up to a volume of 2 mL andthen subjected to GC-MS analysis. The black residue waseluted with 100 mL chloroform and analyzed.The black deposit from the C 137 M and C 137 fragmentssurface were labeled sample 1 and sample 2, respectively.These samples of very small size (around 1 mg) weredissolved under sonication (10 min) in 0.5 mL chloroformand filtered using cellulose filters fitted to a luer locksyringe. The resulting solutions were analyzed by GC-MS.Chromatographic separation was performed at 1 mL/ min helium carrier gas flow rate using the followingtemperature program: start at 100 o C, ramping up to 320 0 C at a 10 degrees/min rate and then isothermal regime upto a final time of 60 min. Pressure increased from 81 psi atthe analysis start up to 165 psi at the finish. Injector port was heated to 250 0  C and the injection volume was 5 µL with a split flow of 10 mL/min. The high injection volumecoupled with low split flow assured a good sensibility andreliable detection. Electron impact provided the ionizationsource, at 70 eV. The scanning range was set at 50-650atomic mass units for 0.41 s, at 300 V multiplier offset.Infrared spectra were recorded on Tensor 21 infraredspectrophotometer with ATR module from Bruker. Results and discussions The chromatogram of the reference sample solutionobtained after hexane elution from open column can benoticed in figure 1. At the short retention time wereexpected the most volatile components, consisting mainly of linear or branched terpenoid hydrocarbons (fig. 2 A is anextended part of chromatogram from figure 1 up to min14). The mass spectra were almost identical and consistof fragmentation patterns characteristic for alkanes (fig. 2 A and 2 B). Fig. 1. Total ion chromatogram fromthe hexane solution of bitumenreference sampleFig. 2. Extended part up to min 14 (A) of chromatogram from figure 1, massspectrum of the 7.48 min peak (B) andmass spectrum of the11.44 min peak (C).  REV. CHIM. (Bucharest) ♦   63 ♦  No.5 ♦  2012 472 The reconstructed ion chromatograms, presented infigure 3 (the first 25 min), were obtained by using thecharacteristic biomarkers for terpanes (m/z=191) andsteranes (m/z=217). As these biomarkers arecharacteristic to a large number of petroleum types, it wasconcluded that this sample srcinates from petroleumsource.Identical results were obtained for sample 1 and 2, withbetter amplitude for the former. The total ionchromatogram of the chloroform solution from fragmentC137 M, named sample 1, is presented in figure 4 A. Twomajor peaks, corresponding to retention times of 18.37and 22.79 min can be noticed. The other peaks are due tocolumn bleeding and their spectra consist mainly of m/ z=73 and m/z=281 ions, characteristic for silanes. Thenormalized current ion level of this chromatogram is around10 5 counts, which is two orders of magnitude lower thanthat of the reference sample. The baseline subtraction of this weak signal is presented in figure 4 B (for the 18.37minutes peak) and in 4 C (for the 22.79 min peak). Thebase peak intensity of 10 4 counts, characteristic for thesepeaks, indicates the low concentration of the maincomponents in the mixture. The characteristic peaks of 4B, found at 189 and 207 m/z were assigned to lupeol(scheme 2) using the library search function [8]. Similarly,the 189 and 203 m/z peaks of 4 C were assigned to betuline(scheme 2). These two substances are known biomarkersfor birch bark tar, especially when found together [9]. Thelupeol mass spectrum has characteristic peaks at 189 and207 m/z but also at 55, 69, 81, 95, 109 and 121 m/z [9]. A careful analysis of 4 B and 4 C spectra has shown thepresence of the former series of peaks shifted. This can beexplained by the dehydration of lupeol and betuline [10].To a more careful analyze of chromatogram from figure4 up to retention time to 15 min we can see a series of peaks due to of column bleeding. However chromatogramhas very small peaks with normalized level of ion currentabout 10 3  counts that correspond to alkanes (fig. 5chromatogram and spectra). These facts shows a mixtureof birch bark tar with natural bitumen.IR spectrum of lupeol presents a very intensely broadband at 3384 cm -1  was observed for the O-H bond vibration Fig. 3. Reconstructed ionchromatograms fromfigure 1 for m/z=191indicating terpanes andreconstructed ionchromatograms m/z=217indicating steranesFig. 4. Chromatogram for sampleno 1, fragment C 137 M. Total ionchromatogram (figure 4 A) withmajor peaks: 18. 37 min., figure 4B the corresponding spectrumand 22.79 min. - figure 4 C thecorresponding spectrum.  REV. CHIM. (Bucharest) ♦   63 ♦  No. 5 ♦  2012  473 of hydroxyl group and moderately intense band at 1192cm -1  was observed for the C-O bond vibration of C-OH group.The out of plane C-H vibrations of the unsaturated part wasobserved at 826 cm -1 . The corresponding C=C vibrations were shown around 1654 cm -1 as weakly intense band.The stretching and bending vibrations of methyl part werenoticed by the intense band 2916 cm -1  and mediumintensity band at 1460 cm -1 . Vibration of the methylenicpart was shown by the band at 2851 cm -1  and the mediumband at 1548 cm -1 . The moderate intense band at 764cm -1  was attributed to the rocking movement of methylenicpart. The corresponding C-C vibration was shown as weakintense band at 1033 cm -1  [11, 12].IR spectra of an extract of birch bark tar were compared with IR spectrum of black organic layer used on Neolithicdecorated ceramic. Both spectra contains specific bandsto 2850 cm -1  and 2919 cm -1  corroborated with mediumintensity band from 1458 cm -1  confirm that the blackorganic layer from Neolithic decorated ceramic containingmainly    birch bark tar than natural bitumen. Conclusions The black colored layer found on neolithic ceramicfragments, excavated from the “Porþ Corãu” archaeologicalsite was analyzed by GC-MS and FT-IR. The layer was foundby comparison with the reference samples to be composedof a mixture of birch bark tar and natural bitumen. Thismixture is predominantly composed of birch bark tar. Scheme1. Characteristic fragmentation of polycyclic terpenoidhydrocarbonFig. 5. Extended chromatogram from sample no. 1, fragment C 137 M. (A) and alkanesmass spectra (B, C)Scheme 2 The analysis of this ancient material represented achallenge due to the chemical complexity of the material.The results obtained in this study are in accordance withhistorical data and come to enrich our knowledge aboutthe past, being of great importance for future archeologicalresearch. The results presented in this paper are also highly relevant for the choosing of restoration methods andmaterials as well as in making the right choice of adequatepreservation conditions for the ceramic fragments.GC-MS has proved as a tool suitable for the analysis of the very small samples of archeological materials. Basedon the target analysis of characteristic biomarkers we havedemonstrated the organic nature of the samples. Moreover,the biomarker analysis has enabled the determination of the chemical composition of the investigated samples. Thisinstrumental analysis approach, presented herein, is partof a larger ongoing study aimed at the identification andcharacterization of black layers found on various ceramicfragments, found in different Romanian archeological sites.  Acknowledgement: Polixenia Georgeta Popescu thanks for the financial support offered by the University „Politehnica” of Bucharest - POSDRU  ID 7713. References 1. BÃCUEÞ-CRIªAN S., ªantierul arheologic “Porþ Corãu”, CCA, 2010,p. 2202. PETERS K.E, WALTERS C.C, MOLDOWAN J.M., The Biomarker guide, 2 , Cambridge University Press, Second edition, 2005, p. 495
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