Advanced combined application of micro-X-ray diffraction/micro-X-ray fluorescence with conventional techniques for the identification of pictorial materials from Baroque Andalusia paintings.

The process of investigating paintings includes the identification of materials to solve technical and historical art questions, to aid in the deduction of the original appearance, and in the establishment of the chemical and physical conditions for adequate restoration and conservation. In particular, we have focused on the identification of several samples taken from six famous canvases painted by Pedro Atanasio Bocanegra, who created a very special collection depicting the life of San Ignacio, which is located in the church of San Justo y Pastor of Granada, Spain. The characterization of the inorganic and organic compounds of the textiles, preparation layers, and pictorial layers have been carried out using an XRD diffractometer, SEM observations, EDX spectrometry, FT-IR spectrometry (both in reflection and transmission mode), pyrolysis/gas chromatography/mass spectrometry and synchrotron-based micro-X-ray techniques. In this work, the advantages over conventional X-ray diffraction of using combined synchrotron-based micro-X-ray diffraction and micro-X-ray fluorescence in the identification of multi-layer paintings is demonstrated.

Gas chromatographic-mass spectrometric analysis of products arising from pyrolysis of amino acids in the presence of hexamethyldisilazane.

Alpha-amino acids were pyrolysed at 600 degrees C in the presence of hexamethyldisilazane (HMDS) and the formed volatile products were analysed on line by gas chromatography-mass spectrometry (GC-MS). Glycine, alanine, valine, leucine, isoleucine, norleucine, methionine, phenylalanine yielded principally the trimethylsilyl (TMS) ester of the parent amino acid. TMS esters of carboxylic acids arising from reductive deamination were observed for serine, threonine and aspartic acid. Decarboxylation resulted in the formation of amines which represented abundant products released from tyrosine, cysteine and methionine. Cyclic compounds arising from the condensation of two amino acids were revealed as characteristic products of glycine, alanine, serine, proline and hydroxyproline. Degradation products of the side chain were released at relatively high levels from tryptophane, tyrosine and hystidine. Since each amino acid produced a characteristic distribution of TMS products, in-situ pyrolysis/silylation with HMDS may find application as a screening technique for the detection of amino acids and related materials in complex matrices. The potentiality of the procedure was tested on a dipeptide (Tyr-Leu).

High performance liquid chromatography versus gas chromatography in the analysis of proteinaceous painting ligands.

High performance liquid chromatography (HPLC) and gas chromatography (GC) were compared for the analysis of the amino acid composition in painting ligands.

Examination of guanosine and xanthosine nucleotides by HPLC and electrochemical detection.

The suitability of electrochemical detection (ECD) following HPLC separation of guanosine, xanthosine and adenosine nucleotides has been evaluated. Separation of five monophosphates of guanosine was achieved by using a reversed-phase column; di- and triphosphates have also been separated from monophosphates. Adenosine compounds are insensitive to ECD.

Preparation, mesomorphic properties and behaviour of 4,4'-biphenylenedibenzoates as stationary phases in gas chromatography.

This paper describes the preparation, mesomorphic properties and behaviour as stationary phases of a series of biphenylenedibenzoates. These compounds exhibit broad mesomorphic ranges with high solid-crystal-liquid-crystal transition temperatures, and give relatively short retention times in the determination of polynuclear aromatic hydrocarbons. The chromatographic selectivity for linear and planar structures is confirmed.

Photometric and electrochemical detection of purine and pyrimidine compounds in reversed-phase and ion-exchange high-pressure liquid chromatography.

An investigation of the optimal conditions for the determination of selected purine and pyrimidine compounds has been made by studying the separation efficiency of reversed-phase columns and ion-exchange columns and comparing the sensitivity of photometric and electrochemical detectors. The combination of ion-exchange HPLC with electrochemical detection proved very good for the separation of electroactive compounds, under the experimental conditions studied. Both types of column allow detection at the picomole level. In general the electrochemical detector appears to be the more sensitive of the two types.

Use of enzymatic catalysis with E.C. 1.2.3.2 xanthine oxidase for the kinetic determination of V(V) at low concentrations.

An enzymatic kinetic method for the determination of V(V) is described, based on the activation of xanthine oxidase-catalysed NADH oxidation, in the presence of xanthine, dithiothreitol and Ag(+) ions. Under these conditions the activating power of V(V) was found to be enhanced. The linear relationship between relative enzyme activity and V(V) concentration allows the enzymatic determination of vanadium in the concentration range 20-500 ng ml , the maximum relative error being +/- 3%, and relative standard deviation less than +/- 2.2%. Possible interferences have been studied.

Pulse polarography of nitrosated GPC fractions of humic acids.

A pulse polarographic method for the analysis of humic acids fractionated by gel permeation chromatography is described. It is concluded that the pulse polarography of the nitroso-derivatives, already reported as an analytical method for the determination of humic acids, really gives responses due to the presence of iron in the samples. Atomic-absorption measurements confirm this conclusion quite unambiguously.