Antonio Doménech-Carbó

Electroanalytical chemistry for the analysis of solids: Characterization and classification (IUPAC Technical Report)

Solid state electroanalytical chemistry (SSEAC) deals with studies of the processes, materials, and methods specifically aimed to obtain analytical information (quantitative elemental composition, phase composition, structure information, and reactivity) on solid materials by means of electrochemical methods. The electrochemical characterization of solids is not only crucial for electrochemical applications of materials (e.g., in batteries, fuel cells, corrosion protection, electrochemical machining, etc.) but it lends itself also for providing analytical information on the structure and chemical and mineralogical composition of solid materials of all kinds such as metals and alloys, various films, conducting polymers, and materials used in nanotechnology. The present report concerns the relationships between molecular electrochemistry (i.e., solution electrochemistry) and solid state electrochemistry as applied to analysis. Special attention is focused on a critical evaluation of the different types of analytical information that are accessible by SSEAC.

Electrochemical Methods in Archaeometry, Conservation and Restoration

Application of Instrumental Methods in the Analysis of Historic, Artistic and Archaeological Objects.- Identification of Species by Electrochemical Methods.- Resolution of Multicomponent Systems and Speciation.- Quantitative Methods.- Electrochemical Basis of Corrosion of Cultural Objects.- Electrochemistry in Treatment and Conservation of Metal Artifacts.

Electrochemical identification of flavonoid dyes in solid work of art samples by abrasive voltammetry at paraffin-impregnated graphite electrodes.

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 dragoons blood, weld, old fustic, gamboge, Brazilwood and logwood (Campeche wood) attached to paraffin-impregnated graphite electrodes in contact with 0.25M HAc+0.25M NaAc aqueous buffer display characteristic peaks in the potential region between +0.85 and -0.85V versus AgCl/Ag. Sequential experiments in contact with 0.05M AlCl(3) and 0.05M Na(2)MoO(4) plus HAc/NaAc and 0.05M H(3)BO(3)+0.10M NaOH solutions also provide dye-characteristic signals allowing for an unambiguous identification of each one of the pigments. Individual pigments were satisfactorily identified in mixtures of pigments and real samples from textile pieces found in Castellfort (Valencian Region, Spain) attributed to the 15th century production of local textile workshops.

Dating Archeological Lead Artifacts from Measurement of the Corrosion Content Using the Voltammetry of Microparticles

A methodology for dating archeological lead artifacts based on the voltammetry of microparticles is described. This methodology is based on the comparison of the height of specific voltammetric features from PbO(2) and PbO corrosion products formed under long-term alteration conditions. Calibration of the method was performed with the help of a series of well-documented lead pieces from the funds of different museums of the Comunitat Valenciana (Spain) covering from the fifth century B.C. to present day. The variation of peak currents with the time of corrosion can be fitted to the same potential rate law as that found by Reich (α = 0.070 ± 0.005), using measurements on the Meissner fraction in the superconducting state of lead. The proposed electrochemical methodology enables the dating of archeological lead artifacts with a time-dependent uncertainty estimated to be ±150 years for the most ancient samples in this study.

Analytical study of proteinaceous binding media in works of art by gas chromatography using alkyl chloroformates as derivatising agents

In this work, we present the results obtained in an analytical study of the different types of proteinaceous binding media most commonly used in paintings, using GC-FID as the technique of analysis and GC-MS as a confirmatory technique. The application of this methodology requires prior hydrolysis of the proteins in the binding media to obtain free amino acids and then volatile derivatives, in this case by reaction with chloroformates due to advantages of speed, safety and the aqueous medium in which the reaction occurs. The method proposed for the proteinaceous binding media study is to calculate the proportions of the different amino acids with respect to alanine. This method provided good characterisation of different binding media, such as pork gelatine, beef gelatine, albumin, egg white and casein. The proposed method is used for the identification of binding media (including mixtures of binders) present in real samples from paintings in the city of Valencia, Spain.

Voltammetric analysis of iron oxide pigments

Eighteen earthy and four pure synthetic pigments containing alpha-Fe2O3 (hematite), alpha-FeOOH (goethite) and poorly crystalline Fe and Mn oxide species were analyzed by voltammetry of microparticles. Three natural samples were subjected to an interlaboratory test to evaluate the reproducibility of the voltammetric peak potentials and peak shapes. The results confirmed that linear-sweep voltammetry is able to distinguish between poorly crystalline, ferrihydrite-like oxides and well-crystalline hematite and goethite and to detect XRD-amorphous Mn(III,IV) oxides via the peak occurrence. Voltammetry is further able to distinguish between pigments containing well-crystalline goethite (according to its structural features) and hematite (according to its particle size). The microsamples of primers from two baroque paintings were also analyzed by XRD and voltammetry and shown to be analogous to common clayey ochres.

Identification of lead pigments in nanosamples from ancient paintings and polychromed sculptures using voltammetry of nanoparticles/atomic force microscopy

Voltammetry of nanoparticles coupled with atomic force microscopy was used to identify lead pigments in nanosamples proceeding from works of art. Upon mechanical attachment of few nanograms of sample to a graphite plate, well-defined voltammetric responses were obtained for lead orange, lead yellow, lead white, litharge, minium, Naples yellow, and tin-lead yellow, allowing for an unambiguous identification of such pigments. Atomic force images provide evidence for the occurrence of pigment-characteristic reduction processes accompanied by metal deposition on the graphite substrate. Electrochemical parameters are used for pigment identification. Application to the method for identifying lead pigments in different model binder+pigment specimens and pictorial samples from the canvas painting collection (anonymous, 17th century) of the Saint Joseph Church in Taormina (Italy), the frescoes painted by Antonio Acisclo Palomino y Velasco (1698) in the vault of the Sant Joan del Mercat church in València (Spain) and an anonymous polychromed sculpture (16th century) representing a Martyr Saint from Alacant (Spain) is described.

Identification of Synthetic Resins Used in Works of Art by Fourier Transform Infrared Spectroscopy

Differentiation between the synthetic polymers used in former restorations of works of art and the original materials used by the artist is of great interest; such differentiation is needed to establish an adequate process of restoration for the work of art. A specific method of sample preparation based on a filtration and deposition-evaporation sequence is proposed, which permits the separation and preconcentration of the synthetic polymer that is being analyzed and avoids problems arising from the simultaneous interpretation of IR spectra obtained from complex mixtures of organic and inorganic compounds present in small artistic samples. In addition to the identification of characteristic IR absorption bands, quantitative diagnostic criteria based on two-dimensional diagrams of relative intensity of selected peaks have been developed. Standards of acrylic, alkyd, cellulose nitrate, epoxy, ketone, poly(vinyl acetate), polyurethane, silicone synthetic polymers and semi-synthetic wax used as binding media, adhesives, and coatings have been prepared by this proposed experimental procedure, and IR spectra have been obtained. Finally, several samples from paintings and artistic objects dating from the 16th to the 20th century have been analyzed, and synthetic and semi-synthetic organic materials have been successfully identified by comparison with the standards using the proposed method of analysis.

Application of the voltammetry of microparticles for dating archaeological lead using polarization curves and electrochemical impedance spectroscopy

The application of the voltammetry of microparticles methodology to date archaeological lead artifacts, based on the time-dependent formation of different layers of lead oxides, whose relative amount can be estimated from polarization curves and electrochemical impedance spectroscopy (EIS), is presented. This approach is complemented by additional data using square wave voltammetry data. Calibration of the method was performed with the help of a series of well-documented, lead pieces from the funds of different Spanish museums, covering since the 7th century BC to nowadays.

Electrochemical identification of metal ions in archaeological ceramic glazes by stripping voltammetry at graphite/polyester composite electrodes

The electrochemical response of metal ions in different samples of coloured ceramic tin-lead glazes attached to graphite/polyester composite electrodes is described. In addition to the ubiquous signals for lead, reductive dissolution processes are followed by anodic stripping peaks for Co, Cu, Sb, Mn, Sn and Fe, enabling the direct identification of such elements in microsamples proceeding from archaeological glazed tiles from Valencia (Spain) workshops (16th-18th century). Additional anodic and cathodic peaks corresponding to redox processes involving metal species in solution generated during stripping processes are also used. Peak potentials, Tafel plots and shape parameters are used for characterising the different species.