Critical assessment of the elemental composition of Corning archeological reference glasses by LA-ICP-MS

Corning archeological reference glasses A, B, C, and D have been made to simulate different historic technologies of glass production and are used as standards in historic glass investigations. In this work, nanoseconds (193, 266 nm) and femtosecond (800 nm) laser ablation were used to study the elemental composition of Corning glasses using laser ablation inductively coupled plasma mass spectrometry. The determined concentrations of 26 oxides (Li2O, B2O3, Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, V2O5, Cr2O3, MnO, Fe2O3, CoO, NiO, CuO, ZnO, Rb2O, SrO, ZrO2, SnO2, Sb2O5, BaO, PbO, Bi2O3) are compared with values reported in the literature. Results show variable discrepancies between the data, with the largest differences found for Cr2O3 in Corning A; Li2O, B2O3, and Cr2O3 in Corning B; and MnO, Sb2O5, Cr2O3, and Bi2O3 in Corning C. The best agreement between the measured and literature values was found for Corning D. However, even for this reference, glass re-evaluation of the data was necessary and new values for PbO, BaO, and Bi2O3 are proposed

Intercalation compounds of graphite in atomic absorption spectrometry

The significance of the formation of intercalation compounds of graphite in the atomization process for atomic absorption spectrometric measurements was investigated. The inspection of the graphite surface and subsurface regions was performed by electron probe microanalysis with energy dispersive X-ray spectroscopic (EDX) detection. It was found that chloride forms thermally stable graphite intercalation compounds (GIC) with the graphite of tubes, which was either non-modified or modified with noble metals

Analysis of Fe valence states in iron-gall inks from XVIth century manuscripts by 57Fe Mössbauer spectroscopy

The charge state of Fe in iron-gall inks was studied by 57Fe Mössbauer spectroscopy. Three ancient manuscripts from the 16th century and a set of model samples were characterized. The chemical fingerprint was found to be well defined for the ancient manuscripts whereas the model samples show a larger spread of chemical states. Two different modes of Mössbauer spectroscopy were used in this work: (1) the detection of [gamma]-quanta in the usual transmission mode and (2) the detection of conversion electrons in backscattering geometry in a special parallel plate avalanche counter. The use of these two measuring modes allowed to reveal differences between the chemical features of the core and the surface of the iron-gall ink structures

Topochemical investigation of ancient manuscripts

Various modern instrumental techniques for surface analysis were applied for the non-destructive physico-chemical examination of works of art. As samples, pieces of ancient manuscripts endangered by iron-gall ink corrosion were used. Surface characterisation of the morphology of the cellulose fibres within corroded and non-corroded parts of the manuscript performed by scanning electron microscopy (SEM) showed seriously damaged cellulose fibres in the written parts. The elemental composition of selected parts of the manuscript was determined by energy dispersive X-ray fluorescence analysis (EDX). A more detailed study of the paper surface was then performed by electron probe microanalysis (EPMA). This technique yields the morphological characteristics of the surface as well as element distribution maps over the written area of the investigated manuscript

Modifiers and coatings in graphite furnace atomic absorption spectrometry--mechanisms of action (A tutorial review)

A multitude of different and often contradictory mechanisms for the effects of modifiers and coatings have been proposed. Many of these proposals lack sufficient experimental evidence. Therefore, a series of statements based on our own investigations is given as [`]facts'. Another series of statements is made as [`]fictions' related to erroneous proposals on the functioning of modifiers and coatings in the pertinent literature. Two basic concepts are developed for the sequence of processes leading to analyte stabilization for the two most important groups of modifiers: refractory carbide forming elements of the IVa-VIa groups of the periodic system on the one hand and Pt-group metals on the other hand. These concepts are based on the main reactions of graphite with elements and compounds: carbide formation and intercalation. Most important experimental results leading to this understanding are described: Penetration measurements for modifiers and analytes indicated the subsurface zone down to approximately 10 [mu]m as the essential place for graphite-analyte-modifier interactions. The reason for this phenomenon is an open porosity of the pyrocarbon coating of 5-10% (v/v) into which liquids penetrate upon sample application. This also indicates that modifiers are best applied by impregnation or electrolysis whereas dense coatings are not advantageous. It is also shown that graphite tube assemblies are dynamic systems with a limited lifetime and carbon losses are an essential feature of tube corrosion. Most frequently found erroneous statements are discussed: (a) Particles on the tube surface are responsible for analyte stabilization and retention during pyrolysis. (b) Analyte stabilization is taking place by formation of intermetallic compounds or thermally stable alloys. (c) Experiments are performed with unrealistic concentrations of analytes and/or modifiers. (d) Dense coatings are advantageous. Finally, a functional schedule is given for the three steps of graphite furnace atomic absorption spectrometry (GFAAS): sample application and drying; pyrolysis; atomization. Contrary to the vast amount of literature on this topic it tried to provide the analyst working with GFAAS and in an increasing number working with Solid Sampling-GFAAS with a set of most important statements. This might spare the experimentalist a lot of useless optimization procedures but should lead him to a basic understanding of the complex phenomena taking place in his instrument and during his analytical work