Guido C. Galletti

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.

Pyrolysis/gas chromatography/mass spectrometry monitoring of fungal-biotreated distillery wastewater using Trametes sp. I-62 (CECT 20197)

Distillery wastewaters generated by ethanol production from fermentation of sugar-cane molasses, named vinasses, lead to important ecological impact due to their high content of soluble organic matter and their intense dark-brown color. Taking advantage of the well-known ability of white-rot fungi to degrade an extensive variety of organic pollutants, the capacity of Trametes sp. I-62 (CECT 20197) to detoxify this type of effluents was evaluated. In this work, pyrolysis/gas chromatography/mass spectrometry was applied to the chemical characterization of several fractions of Cuban distillery wastewater as well as to monitoring the changes which occurred after fungal treatment with this white-rot basidiomycete. Maximum effluent decolorization values and chemical oxygen demand reduction attained after seven days of fungal treatment were 73.3 and 61.7%, respectively, when 20% (v/v) of distillery vinasses was added to the culture medium. Under these conditions a 35-fold increase in laccase production by Trametes sp. I-62 was measured, but no manganese peroxidase activity could be detected. The pyrolysis/gas chromatography/mass spectrometry results showed a decrease in a number of pyrolysis products after seven days of fungal treatment, mainly furan derivatives. The decrease in the relative areas of these compounds could be related to the vinasse color-removal associated with melanoidin degradation. All these results indicated the potential use ofTrametes sp. I-62 in the detoxification of recalcitrant distillery vinasses.

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.

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.

Absolute quantitation of lignin pyrolysis products using an internal standard

Abstract A simple method to obtain absolute quantitation of lignin pyrolysis fragments by on-line pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) is proposed. Three compounds were tested as internal standards, i.e. 1,3,5-tri-tert.-butylbenzene, 1,2,4-benzenetricarboxylic acid trimethyl ester and 1,3,5-trimethoxybenzene. The characteristic of the proposed internal standards is that they vaporize in the hot pyrolysis interface during the 3-min equilibration and focus on the top of the GC column, thus avoiding loss of internal standard due to thermal fragmentation. The linearity and reproducibility of response of the standards over a range of concentrations are reported. 1,3,5-Tri-tert.-butylbenzene was selected as the most appropriate among the tested standards to be used in Py–GC–MS of lignin. The correction factors for the main lignin pyrolysis fragments were calculated and a practical application of the proposed method to the analysis of a wheat straw sample is discussed.

Studies on wheat lignin degradation by Pleurotus species using analytical pyrolysis

Abstract The aromatic-ring substitution patterns of p -hydroxyphenyl ( H ), guaiacyl ( G ) and syringyl ( S ) lignin-units are conserved after pyrolytic breakdown enabling analysis of the composition of lignins with different origins. Analytical pyrolysis has been used to investigate lignin degradation by several white-rot fungi including Pleurotus eryngii , a species characterised by the ability to degrade lignin selectively. Using Py-GC/MS it was found that the composition of wheat lignin was modified by P. eryngii causing a decrease of S / G ratio in the residual lignin. Simultaneously, degradation products were incorporated into lignin-polysaccharide complexes. In order to get additional insight on wheat lignin modification by these fungi, the biodegraded samples were permethylated before Py-GC/MS. In this way it was shown that the free phenolic lignin-units (around 50% of the total H and G units and only 6% of S units) were preferentially removed as compared with the etherified ones. Moreover, it was possible to demonstrate that the lignin side-chains were attacked in situ resulting in the increased amounts of ether-linked vanillic and syringic acids, identified as the corresponding methyl esters by Py-GC/MS of permethylated samples. When 50% of wheat lignin was degraded by P. eryngii , the relative abundance of aromatic acids was over 15% of the total lignin derived products. These results validate some of the mechanisms postulated for lignin degradation by white-rot fungi, which were based on simple model compounds.

High-performance liquid chromatographic determination of sulfonylureas in soil and water

Abstract Isocratic and gradient conditions for the separation of four sulfonylurea herbicides, namely chlorsulfuron, metsulfuron, chlorimuron and thifensulfuron, by reversed-phase high-performance liquid chromatography (HPLC) on C6 and C18 columns were established. Liquid-liquid (LL) and solid-phase extraction (SPE) procedures for the extraction and concentration of the herbicides from water and soil samples were tested. LL and SPE recoveries, HPLC detection limits and repeatability and dependence of the capacity factor on mobile phase composition are discussed. Typical chromatograms are shown.

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.

Pyrolysis-gas chromatography/Mass spectrometry analysis of phenolic and etherified units in natural and industrial lignins

Milled-wood lignin (MWL) from Carpinus betulus, Eucryphia cordifolia, Picea abies, Pinus sp. and Bambusa sp., Kraft lignin from Fagus sylvatica and Eucalyptus globulus, and alkali lignin and hemicellulose-linked lignin from Triticum aestivum, were investigated with respect to their composition in phenolic and etherified phenylpropanoid H (p-hydroxyphenyl), G (guaiacyl) and S (syringyl) units. For this purpose, a methodology based on lignin permethylation, followed by pyrolysis-gas chromatography/mass spectrometry, and quantitation of marker compounds (H-, G- and S-type vinylphenols and their methylated derivatives) in single-ion chromatograms, was developed. The phenolic content in the samples analyzed ranged from 2% of total units in hemicellulose-linked lignin to near 70% in Kraft lignins. Softwood MWL showed higher amounts of phenolic units than MWL from annual plants and hardwoods. It was found that the phenolic content of MWL from the Austral tree species E. cordifolia was unexpectedly high for a hardwood lignin. The significance of this finding in terms of lignin degradability by white-rot fungi, of biotechnological interest, is discussed. Copyright # 1999 John Wiley & Sons, Ltd.

The chemical composition of Black Sea suspended particulate organic matter : pyrolysis-GC/MS as a complementary tool to traditional oceanographic analyses

Abstract A “traditional” description of the abundance and chemical composition of suspended particulate organic matter (POM) in open and coastal waters of the southern Black Sea in June 1996 has been confirmed and extended by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) analyses. Py-GC/MS provided depth profiles of the relative concentrations of twenty three marker compounds characteristic of chlorophylls (CHL), lipids, carbohydrates (CBH) and proteins produced by thermal degradation of the POM retained on the filters. No terrestrial markers, characteristic of lignin or of plant waxes, were observed. Evidence was found for considerable changes in the chemical composition of POM in the water column from the surface down to the sulphidic water layer. In surface-mixed layer, both POC:CHL-a ratios and relative abundances of CBH markers were notably high, suggesting that the suspended POM was mainly composed of detritus. The profiles of both CHL and protein markers exhibit coherent maxima at the base of the euphotic zone, coinciding with the nutricline depth in the central cyclonic eddy, where the bulk POM possessed relatively low C:N ratios. Beneath the 0.1% light depth the absence of intact phytoplankton cells and the presence of bacteria and faecal pellets was accompanied by a change in the protein composition of the POM as shown by the changes in the ratio of pyrrole:indole markers. Lipid markers increased markedly from the euphotic zone into the oxycline and remained almost constant in the suboxic waters; they then decreased in the sulphidic interface, presumably due to consumption of lipids by anaerobic bacteria.