Giuseppe Chiavari

Pyrolysis—gas chromatography/mass spectrometry of amino acids

Abstract Nineteen α-amino acids were pyrolysed at 600°C using an integrated pyrolysis-gas chromatography/mass spectrometry system. Pyrograms, tabulated mass spectra and proposed identifications of the main pyrolysis fragments are reported. Diagnostic pyrolysis fragments were recognised for most of the α-amino acids (with the exception of histidine, glycine, serine, alanine and threonine) and their formation is rationalised by proposing four thermal degradation pathways.

Characterization of soil humin by pyrolysis(/methylation)-gas chromatography/mass spectrometry: structural relationships with humic acids

Abstract Pyrolysis-gas chromatography /mass spectrometry (Py-GC/MS) and Py-GC/MS in the presence of tetramethylammonium hydroxide (TMAH) (pyrolysis methylation-GC/MS) have been used to characterize humin of a representative agricultural soil. Analyses have been performed on humin de-ashed by treatment with HCl-HF (HU) and the results have been compared with those obtained from the corresponding humic acid (HA). Both semiquantitative conventional pyrolysis and pyrolysis methylation agreed in showing that the pyrolytic behaviour of HU is quite different from that of HA, the mass spectrometry pyrograms of the former being characterized by a larger amount of carbohydrates and aliphatic compounds. Pyrolysis/methylation of HU produced methyl esters of aliphatic and aromatic carboxylic acids, methylated carbohydrate derivatives and methyl pyrroles. Peaks diagnostic of the presence of glucose and cellulose have been proposed when pyrolysis is performed in the presence of TMAH.

Analytical pyrolysis of carbohydrates in the presence of hexamethyldisilazane

Abstract The paper describes gas chromatography/mass spectrometry (GC/MS) analysis of the products released from carbohydrates when flash pyrolysed in the presence of hexamethyldisilazane (HMDS). Monosaccharides ( d -glucose, d -mannose, d -galactose) and polysaccharides (cellulose, laminaran, agar) were pyrolysed with HMDS using an off-line apparatus and on-line Py-GC/MS. A series of characteristic trimethylsilyl (TMS) ethers of hydroxylated compounds were released which are proposed as useful markers for the recognition of carbohydrates in complex matrices. The detected products included TMS derivatives of anhydrosugars, hydroxylated pyranones and cyclopentenones, hydroxymethylfuraldehyde, hydroxymethylfurane, di- and tri-hydroxybenzenes. Monosaccharides and related polymers yielded the TMS ethers of the corresponding 1,6-anhydro- d -hexopyranoses and 1,6-anhydro- d -hexofuranoses which were identified by off-line pyrolysis of the parent carbohydrate followed by silylation with HMDS.

The potential of pyrolysis-gas chromatography/mass spectrometry in the recognition of ancient painting media

Abstract Pyrolysis—gas chromatography mass spectrometry is shown to be a rapid technique, requiring no sample work-up, for the recognition of organic materials, namely animal glue, egg yolk and glair, and linseed oil and casein, commonly used as binding media in ancient paintings. Major compounds originating from the thermal decomposition of proteins are identified by their mass spectra and have been diagnostic for glue, glair and casein. C-16, C-18 and other lower molecular weight free fatty acids are significant markers for yolk and linseed oil; however, they are not detectable in their free form when present in low quantities or as salts. In this case, the use of simultaneous pyrolysis—methylation (SPM), by addition of an aqueous solution of tetramethylammonium hydroxide to the sample, is recommended. Chromatograms of pyrolysates of binding media and of samples from original paintings are shown.

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).

In-situ pyrolysis and silylation for analysis of lipid materials used in paint layers

SummaryAlthough pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC-MS) is a useful technique for the rapid characterization of the organic materials used by artists, diagnostic pyrolysis products bearing polar groups, for example carboxylic acids, require derivatization (e. g. methylation) before GC separation. In this study we propose the use of hexamethyldisilazane (HMDS) as an effective on-line derivatizing reagent to prepare the trimethylsilyl (TMS) derivatives of fatty acids released from the pyrolysis of fats. Pyrolysis in combination with HMDS has been applied to the analysis of lipid materials employed as painting media, for example siccative oils and egg.

Nature and decay effects of urban soiling on granitic building stones

A detailed microscopical and chemical examination by SEM + EDAX, XRD and PyGC-MS of black patinas coating the surfaces of urban granitic monuments in Aberdeen and Dublin has revealed a variety of decay features together with a complex chemical composition. Beside sulphate-rich thick patinas composed of a framework of gypsum crystals in which both particulate and gaseous inorganic/organic pollutants are deposited and which are similar to gypsum crusts developing under polluted atmospheric conditions on calcite-bearing stones, thinner, gypsum-free, black surface layers made up of particulate matter embedded in a fine-grained, iron-rich matrix are commonly found. These soiling layers show, relative to the substrate, higher % of P, Ca, S, and Cl. The occurrence of a patinas type against the other is probably controlled by the availability of local SO2 sources. Physical and chemical decay effects on the granitic substrate are more severe when gypsum is present but dissolution and micro fracturing episodes are also observed in iron-rich patinas. The chemical inorganic/organic composition of these surficial layers suggests that pollution induced soiling processes are the main factors resoonsible for their build-up on building facades. On the other hand, microscopic and preliminary chemical evidence does not exclude biological activity as an important agent in the development of iron-rich thin black layers.

Analysis of anthraquinoid and indigoid dyes used in ancient artistic works by thermally assisted hydrolysis and methylation in the presence of tetramethylammonium hydroxide

Abstract Thermally assisted hydrolysis and methylation (THM) in the presence of tetramethylammonium hydroxide (TMAH) was applied to the analysis of red dyes based on the 9,10-anthracenedione skeleton (anthraquinone), namely alizarin, quinizarin, purpurin, carminic acid, and the blue pigment indigo. Alizarin and purpurin are the principal coloured compounds of madder, and carminic acid of cochineal red. Synthetic dyes were dissolved in aqueous TMAH, pyrolysed at 700°C for 10 s and the evolved thermochemolytic products were analysed by gas chromatography/mass spectrometry (GC/MS). The resulting chromatograms of all the madder dyes were characterised by the presence of the methyl esters of 1,2-benzenedicarboxylic acid (dimethyl- o -phthalate) and benzoic acid. In addition, thermochemolysis of alizarin and quinizarin afforded 1,2-dimethoxyanthraquinone and 1,4-dimethoxyanthraquinone, respectively. Carminic acid produced a series of methylated fragments deriving from both the substituted anthraquinoid moiety and the glycosidically-C-linked glucose. Finally, the principal thermochemolysis products of indigo were the N -methylated derivatives of 2-amino benzoic acid methyl ester followed by methylated aniline and indoles. The potential of THM as a rapid technique for the identification of dyes in real samples was illustrated by the analysis of madder lake, cochineal lake, and natural indigo dispersed in a binder.

Electrochemical detection in the high-performance liquid chromatographic analysis of plant phenolics.

The electrochemical behaviour of several phenolic compounds of biological interest in vegetable materials was studied. Oxidation potentials of the examined compounds and voltammetric curves of some representative phenols are reported. As a practical application of electrochemical detection in HPLC, the analysis of monomeric units emanating from nitrobenzene oxidative hydrolysis of wheat straw lignin is described. Electrochemical detection simplifies the analysis, permitting the direct injection of the reaction mixture without interference from nitrobenzene. Aniline formed by the reduction of nitrobenzene is also detectable and may be used as an oxidisability index of the vegetable matter.

Characterisation of Natural Resins by Pyrolysis - Silylation

SummaryMany organic materials release polar compounds containing-OH groups when subjected to pyrolysis. To improve GC detection of such polar compounds derivatisation with the silylating reagent hexamethyldisilazane (HMDS) can be achieved in situ while pyrolysing the sample (pyrolysis—silylation).In this study pyrolysis—silylation in combination with GC-MS was applied for the analysis of natural resins, utilised in artistic fields namely sandarac (Cupressaceae), Manila copal (Araucariaceae), colophony, Venice turpentine, Strasbourg turpentine (Pinaceae), dammar, mastic, and shellac.Pyrolysis-silylation of natural resins resulted in the formation of several silylated compounds characteristic of the different kinds of resins.The trimethylsilyl (TMS) ester of sandaracopimaric acid was a prominent compound released from sandarac. Pinaceae resins produced TMS esters of pimaric, isopimaric, methyl dehydroabietic and abietic acids. TMS esters of linear aliphatic and aromatic acids were generated from shellac. Distinctive though as yet unidentified silylated compounds were released from Manila copal and triterpenic resins.