Voltammetric methods applied to identification, speciation, and quantification of analytes from works of art: an overview

Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.     

THE INTERACTION OF IONIC SURFACTANTS-RESINS FOR IMPROVING EXHAUSTION ADHESION AND SPREADING OF PREPOLYMERS ON KERATIN FIBRES

A study of the effect of the aggregates formed between Hercosett and alkylsulphates (C₈-C₁₄) in preventing the shrinkage of wool samples pretreated with hydrogen peroxide is reported and a kinetic study of the formation of these aggregates as well as a mechanism by which they exhaust on wool fibres are suggested.     

The ternary system propyl propanoate+ hexane+chlorobenzene at 298.15 k

Differential thermal analysis shows many interesting properties that allow for prompt finding the place (p,T) and characteristics (endothermic, exothermic) of a phase transition or chemical reaction. In application to reactive sintering under active gas atmosphere at high pressure despite of numerous technical problems encountered during DTA measurements we found its unique possibilities. That allows for quantitative estimation of nitrogen involved in reaction of phase transition from the hexagonal phase to the cubic phase of MoN, and vice versa, in high gas pressure condition. DTA high gas pressure measurement system has the maximum operate temperature 2000°Cat pressure 2 GPa. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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 methodology is of considerable interest due to the requirements of minimum sampling that usually involves the analysis of works of art. A chemometric study has been developed to adjust the optimal working conditions of the proposed derivatisation method in which chromatographic peak areas of the larixyl acetate derivative and the abietic acid derivative referred to n-hexadecane as internal standard have been compared. Samples of Venetian turpentine naturally aged have been used in this study. Finally, the efficiency of the proposed derivatisation method has been tested on other diterpenic resins and pigments commonly used in fine arts such as Strasbourg turpentine, Canada balsam, colophony, copper resinate and a sample from a Renaissance Altarpiece.     

The evaluation of electronic extracule and intracule densities and related probability functions in terms of Gaussian basis functions

The evaluation of the basic two-electron integrals involved in the calculation of extracule and intracule densities is described. Expressions are given for the evaluation of the related spherically averaged, longitudinal, and transverse probability functions from wave functions constructed from Gaussian basis sets. All results are expressed in closed analytical forms which are suited to efficient coding. Given that certain pair densities can be related to experimental scattering cross sections, the formulae reported herein will facilitate further comparison between experiment and theory and lead to a more comprehensive understanding of the electronic structures of molecules.     

Application of XRF,XRD, thermal analysis,and voltammetric techniques to the study of ancient ceramics

An in-depth chemical-analytical study has been performed on biscuit and mortar from 17th-18th century tiles from a mediaeval hermitage in the province of Valencia (Spain). Representative samples were chosen from the tile fragments available, using appearance, essentially color and consistency, as the criterion. The chemical composition was analyzed by X-ray fluorescence of the samples in the form of glass disks after a previous qualitative study to choose the standard materials for calibration and the experimental conditions used in the analysis. X-ray diffraction of the samples provided information about the mineralogical composition which was consistent with the firing of the original materials; it also gave information about the range of temperatures used in the firing. From thermal gravimetric analysis of the limestone, and from historical considerations, it was possible to deduce the raw materials used and their approximate composition in the tiles. In the same way it was possible to determine the nature of the mortars used to fix the tiles. Cyclic voltammetric study of the iron(II) and iron(III) system in the biscuit showed the simultaneous presence of both oxidation states, corroborating the results.     

A Study on Corrosion Processes of Archaeological Glass from the Valencian Region (Spain) and its Consolidation Treatment

The combined use of scanning electron microscopy/energy dispersive X-ray microanalysis (SEM/EDX) and square wave voltammetry (SQWV), is used for studying the corrosion processes that have taken place in buried glass from different archaeological sites in the Valencian Region (Spain). The procedures permit a parallel investigation of morphology and chemical composition. Determination of the chemical composition of the glasses and their alteration crust and identification of the elements responsible for the colour has been also carried out using energy dispersive X-ray microanalysis. The electrochemical response of samples attached to paraffin-impregnated graphite electrodes reveals the presence of different iron and manganese oxide species in the browning areas of the corroded glass. Image analysis applied to microphotographs obtained by means of SEM led to the determination of morphological parameters concerning the corrosion phenomena occurring on the surface of the fragments such as thickness of the corrosion layer and its laminated structure. Additionally, measurement of the thickness of the film of polymer used as coating in the consolidation treatments has been carried out using cryo-scanning electron microscopy (cryo-SEM) combined with image analysis.     

Analytical study of canvas painting collection from the Basilica de la Virgen de los Desamparados using SEM/EDX, FT-IR, GC and electrochemical techniques

A new method, based on the combined use of scanning electron microscopy-x-ray microanalysis, Fourier transform infrared spectroscopy, gas chromatography and differential pulse voltammetry, is proposed which permits a parallel investigation of organic and inorganic materials and the characterization of the artistic technique employed in canvas painting. The proposed method has led to analyze succesfully the canvas painting collection exhibited in the Basílica de la Virgen de los Desamparados (Valencia, Spain) which includes art works from 17th to 20th century.