0000000000047002
AUTHOR
M. T. Doménech-carbó
Characterization of bile acids and fatty acids from ox bile in oil paintings by gas chromatography?mass spectrometry*1
Characterization of ox bile, traditionally used in painting, is of interest in the fields of archaeometry and conservation and restoration of works of art. Bile acids, fatty acids (F), and cholesterol found in ox bile have been identified using a derivatization method that combines the formation of ethyl esters from the carboxylic groups and the trimethylsilyl ethers from hydroxyl groups. This method of analysis is consistent with these others proposed by the authors to analyze drying oils, proteins, and diterpenic resins usually used as binders and varnishes by the painters. Bile acids from binary samples such as animal glue/ox bile, casein/ox bile and Arabic gum/ox bile have been successf…
H-Point Standard Addition Method Applied to Voltammetry of Microparticles. Quantitation of Dyes in Pictorial Samples
A solid-state electrochemical application of the H-point standard addition method (HPSAM) for quantifying two electroactive compounds, A, B, that produce strongly overlapped voltammetric peaks is described. It is based on peak current measurement in square-wave voltammograms recorded for solid samples containing a reference compound R, upon additions of a A- (or B-) containing standard compound. The method allows to the determination of the mass fraction of A and B by applying the H-point standard addition method to solid state voltammetry. The quotients between the currents measured at two selected potentials and the peak current of R vary linearly with the mass ratio of the added standard…
Electrochemical Characterization and Dating of Archaeological Leaded Bronze Objects Using the Voltammetry of Immobilized Particles
Financial support from the MINECO Projects CTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P, which are supported by ERDF funds, is gratefully acknowledged. We wish to thank the Fondo de Arte y Patrimonio of the Universitat Politecnica de Valencia; the Museu de Prehistoria of Valencia, and its director Helena Bonet and curator Jaime Vives-Ferrandiz; and the Museu Municipal of Xativa and its director Angel Velasco. We also wish to thank Dr Jose Luis Moya Lopez and Mr Manuel Planes Insausti (Microscopy Service of the Universitat Politecnica de Valencia) for technical support.
Voltammetric Identification of Lead(II) and (IV) in Mediaeval Glazes in Abrasion-Modified Carbon Paste and Polymer Film Electrodes. Application to the Study of Alterations in Archaeological Ceramic
Direct identification of lead(II) and (IV) in glazed ceramics by cyclic voltammetry and differential pulse voltammetry is described. Characteristic cathodic and anodic profiles are obtained for microsample coatings in Paraloid B72-film electrodes immersed in NaCl and HAc/NaAc media. The electrochemical response of PbO, PbO2 and Pb3O4, and a series of test specimens of glaze is compared with that of microsamples extracted from the glaze of blue and white decorated ceramic produced in Manises (Spain) in the 15th century which have been buried in a damp place. Under abrasive conditions, striping peaks at –0.12 and –0.25 V (vs. SCE) appear for Pb(IV) centers and, at –0.55 and –0.75 V, for Pb(II…
Electrochemical identification of flavonoid dyes in solid work of art samples by abrasive voltammetry at paraffin-impregnated graphite electrodes.
Abstract An electrochemical method for identifying flavonoid-type dyes in microsamples from works of art is reported. Square wave voltammograms of natural insoluble dyestuffs based on flavonoid structure dragoon's blood, weld, old fustic, gamboge, Brazilwood and logwood (Campeche wood) attached to paraffin-impregnated graphite electrodes in contact with 0.25 M HAc + 0.25 M NaAc aqueous buffer display characteristic peaks in the potential region between +0.85 and −0.85 V versus AgCl/Ag. Sequential experiments in contact with 0.05 M AlCl 3 and 0.05 M Na 2 MoO 4 plus HAc/NaAc and 0.05 M H 3 BO 3 + 0.10 M NaOH solutions also provide dye-characteristic signals allowing for an unambiguous identi…
ELECTROCHEMISTRY AND AUTHENTICATION OF ARCHAEOLOGICAL LEAD USING VOLTAMMETRY OF MICROPARTICLES: APPLICATION TO THE TOSSAL DE SANT MIQUEL IBERIAN PLATE
The authors wish to thank the Museu de Prehistoria de Valencia, Museu Arqueologic de Borriana and Museu Municipal de Montcada for the access to their archives and funds. Financial support is gratefully acknowledged from the Spanish 'I+D+I MICINN' project CTQ2008-06727-C03-01 and 02/BQU, supported by ERDEF funds. The authors wish to thank Mr Manuel Planes i Insausti and Dr Jose Luis Moya Lopez, the technical supervisors responsible for the UPV Electron Microscopy Service.
Electrochemical Characterization of Archaeological Tin-Opacified Lead-Alkali Glazes and Their Corrosion Processes
The electrochemical response of weathered and unweathered archaeological tin-opacified glazes attached to paraffin-impregnated graphite electrodes is described. Upon comparison with the square wave voltammetric response of SnO2, PbO and PbO2, Sn- and Pb-centered reduction processes can be characterized. Reduction of Sn(IV) involves the stepwise formation of solid Sn(II) and Sn metal, successively, at potentials of −0.08 and −0.55 V vs. AgCl/Ag. Reduction of network-modifier Pb(II) in glazes occurs at −0.5 V and is accompanied by the reduction of network-forming Pb(IV) at potentials ranging from +0.65 to +0.20 V, confirming the presence of such centers in glazes. Voltammetric data suggest th…
Identification of Manganese(IV) Centers in Archaeological Glass Using Microsample Coatings Attached to PolymerFilm Electrodes
Identification of MnO2 nodulae in archaeological glass by linear scan and differential pulse voltammetry using abrasive-conditioned microsamples attached to polymer film (Elvacite 2044) electrodes is described. Voltammetric responses for manganese-containing samples parallels to those obtained for β- and γ-MnO2 upon immersion of modified electrodes into NaCl, KCl and acetic/acetate aqueous media. The observed electrochemical response provides information on the open microporous structure of the MnO2 forms and the conditions of their formation during the weathering process of buried glass.
Suppression of pigment interference in the gas chromatographic analysis of proteinaceous binding media in paintings with EDTA.
A method to suppress the interference of pigments in the analysis of proteinaceous media used in paintings is presented in this paper. This method is based on the formation of metallic ion-ethylenediaminetetraacetic acid (EDTA) complexes previous to the derivatisation process, using ethyl chloroformate (ECF), to transform the amino acids in N(O,S)-ethoxycarbonyl (EOC) ethyl esters. Test specimens, containing different proteinaceous media such as albumin, porcine gelatine and casein mixed with lead white, chalk, verdigris and raw Sienna have been prepared for carrying out this study. Different pH conditions have been probed for the different pigments studied. Values of peak area ratio of ami…
Quantitation of Metal Ions in Archaeological Glass by Abrasive Stripping Square-Wave Voltammetry Using Graphite/Polyester Composite Electrodes
A method for identifying Co, Cu, Sb, Sn, Fe, Zn, and Zr pigments in glasses using square-wave voltammetry as the detection mode is described. It is based on the abrasive attachment of glass microsamples to graphite/polyester composite electrodes. Sample amounts less than 1 μg are used allowing for the study of archaeological samples. In all cases well-defined anodic stripping peaks corresponding to the oxidation of metal deposits generated at potentials ranging from −0.6 to −1.6 V (vs. SCE) are obtained. This response is in agreement with that displayed by the corresponding metal oxides. Quantitative estimates of the relative population of metal ions in glasses are obtained from peak area m…
Electrochemical analysis of the alterations in copper pigments using charge transfer coefficient/peak potential diagrams. Application to microsamples of baroque wall paintings attached to polymer film electrodes
The alteration of copper pigments in art samples was studied by linear scan and cyclic voltammetry using sample-modified Elvacite 2044 film electrodes on the basis of two-dimensional diagrams of charge transfer coefficients calculated from Tafel plots of reductive dissolution processes vs. peak potential. Characteristic voltammetric peaks were obtained for pigments used in the baroque vault frescoes of the Basílica de la Virgen de los Desamparados painted by Antonio Palomino. Results obtained by voltammetric techniques were compared with those from SEM/EDX and FT-IR analysis obtaining a good agreement and leaving to an unambiguous identification of pigments used by Palomino and their altera…
Electrochemical Determination of the Fe(III)/Fe(II) Ratio in Archaeological Ceramic Materials Using Carbon Paste and Composite Electrodes
A method for determining the iron(III)/iron(II) ratio in ceramic materials based on microsample attachment to graphite/polyester composite electrodes is presented. This quotient is of considerable interest for determining the nature and firing conditions of the original materials in archaeological ceramics. The electrochemistry of iron in ceramic materials in acetic/acetate and Na2EDTA aqueous solutions is described in terms of reductive dissolution processes of iron(III) materials and oxidative dissolution processes of iron(II) ones. The iron(III)/iron(II) ratio is determined from peak area measurements in linear scan voltammograms performed in 0.10 M acetic/acetate buffer (pH 4.70) and 0.…
Analytical Study of a Resinous Material Used as Sealing in Ancient Pottery Found in an Archaeological Site by Thermally Assisted Hydrolysis Methylation–Gas Chromatography–Mass Spectrometry, Vibrational Spectroscopy and Light Microscopy
Abstract A resin sample was found in the archaeological site of Lixus (Morocco), belonging to the second century BC. The resinous material was found inside an amphora containing iron remains used in the plug as sealing material to hermetically close the pottery. The resinous sample was studied by several analytical techniques, as thermally assisted hydrolysis and methylation–gas chromatography–mass spectrometry (THM–GC–MS), Fourier transformed infrared spectroscopy (FTIR), and light microscopy. The material was identified as a Pinaceae resin. Therefore, a modern pine resin was also analyzed to consider the influence of aging in the archaeological sample. The ancient material was found not t…
Identification of diterpenes in canvas painting varnishes by gas chromatography-mass spectrometry with combined derivatisation.
A derivatisation method that combines the formation of ethyl esters from the carboxylic groups and trimethylsilyl ethers from hydroxyl groups of the components of diterpenic resins is presented in this paper. This methodology involves two experimental steps: (1) formation of ethyl esters using ethyl chloroformate; and (2) the esterified compounds are lead to react with trimethylsilylimidazole to form the corresponding trimethylsilyl ethers. The main advantage of the proposed method is the possibility of performing simultaneously the analysis of amino acids from proteins, fatty acids from drying oils, and diterpenic compounds from natural resins usually found in works of art. This methodolog…