Maria Chiara Pietrogrande

Determination of synthetic phenolic antioxidants and their metabolites in water samples by downscaled solid-phase extraction, silylation and gas chromatography-mass spectrometry.

The development and performance evaluation of an analytical method dedicated to the comprehensive determination of the most relevant antioxidants and their metabolites in aqueous environmental samples is presented. This was achieved by a miniaturised solid-phase extraction (SPE) with 10mg Oasis HLB cartridges, which allow to achieve a concentration factor of 200, reducing organic solvent wastes (1 mL of ethyl acetate suffices for complete elution) and SPE costs and eliminating the need for solvent evaporation that otherwise compromises the recoveries of butylated hydroxytoluene (BHT) and 2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione (BHT-Q). Analytes were then determined by gas chromatography-mass spectrometry (GC-MS) after derivatisation with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) in a single run. BHT-d(7) and n-propyl-paraben-d(4) (PrP-d(4)) were used as surrogate internal standards. These surrogates allowed obtaining relative recoveries in the 80-110% range for all analytes even with complex wastewater samples and LODs at the 2-44 ngL(-1) level taking into account blank issues often associated to antioxidants analysis. The method was applied to sewage and river waters, showing that the seven analytes could be detected in raw wastewater. BHT and BHT-Q were the most concentrated species in that type of sample (in the 275-871 ngL(-1) range). On the other hand two metabolites of BHT, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) and 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) appeared to be the most ubiquitous species, being found in all samples in the 10-150 ngL(-1) concentration range.

Seasonal variation and source estimation of organic compounds in urban aerosol of Augsburg, Germany.

This study reports a general assessment of the organic composition of the PM(2.5) samples collected in the city of Augsburg, Germany in a summer (August-September 2007) and a winter (February-March 2008) campaign of 36 and 30 days, respectively. The samples were directly submitted to in-situ derivatisation thermal desorption gas chromatography coupled with time of flight mass spectrometry (IDTD-GC-TOFMS) to simultaneously determine the concentrations of many classes of molecular markers, such as n-alkanes, iso- and anteiso-alkanes, polycyclic aromatic hydrocarbons (PAHs), oxidized PAHs, n-alkanoic acids, alcohols, saccharides and others. The PCA analysis of the data identified the contributions of three emission sources, i.e., combustion sources, including fossil fuel emissions and biomass burning, vegetative detritus, and oxidized PAHs. The PM chemical composition shows seasonal trend: winter is characterized by high contribution of petroleum/wood combustion while the vegetative component and atmospheric photochemical reactions are predominant in the hot season.

Spot overlapping in two-dimensional polyacrylamide gel electrophoresis separations: A statistical study of complex protein maps

A statistical approach able to extract the information contained in a two‐dimenisional polyacrylamide gel electrophoresis (2‐D PAGE) separation is here reported. The method is based on the quantitative theory of peak overlapping, a procedure previously developed by the authors and here extended to 2‐D separations. The whole map is divided into many strips in order to obtain 1‐D separations on which the statistic procedure is applied: the developed algorithms, on the basis of spot experimental data (intensity and spatial coordinates) permit to estimate the intrinsic number of components and to single out the specific order present in spot positions. The procedure was validated on computer‐simulated maps. Its applicability to real samples was tested on maps obtained from literature sources. The following important information on protein mixtures can be extracted: (i) the number of proteins can be accurately estimated, on the basis of the spatial coordinates and intensities of spots detected in the 2‐D PAGE map; (ii) the model describing distribution of interdistance between adjacent spots can be identified in both the separation dimensions; (iii) the presence of repeated interdistances in spot positions in the maps can be easily singled out: these regularities suggest specific protein modifications.

Study of the lipophilic character of xanthine and adenosine derivatives. I: RM and log P values

Abstract The RM values of a series of xanthine and adenosine derivatives were measured using silicone reversed-phase thin-layer chromatographic (TLC) and C18 reversed-phase high-performance TLC systems. The two series of data were well correlated. Both were compared with experimental log P and calculated CLOGP values. For xanthine derivatives a good linear relationship was shown between the RM values from the two chromatographic systems and the log P or CLOGP data. For adenosine derivatives the CLOGP values had to be corrected in order to fit the data to the same equation. The TLC data proved to be reliable parameters for describing the lipophilic properties of the test compounds.

Statistical study of peak overlapping in multicomponent chromatograms: importance of the retention pattern

Abstract A general method is reported for evaluating the statistical degree of overlapping (SDO) in a multicomponent chromatogram, whose retention pattern is known and described by the frequency function of interdistances between subsequent single component peaks (interdistance model, IM). The content of SDO is the expected numbers of singlet, doublet, triplet, etc., peaks, as a function of the number of components, the separation performance and the IM. The proposed method is exploited in practice for three cases of IMs: gamma, normal and uniform, which are known to represent a wide variety of cases. Two different approaches are presented and discussed: analytical expression and simulation computation, according to whether the IM can be analytically integrated or not. The advantages and differences of the two approaches are considered, even in the case of negative interdistances (normal case). A real case of chromatographic separation of a multicomponent mixture, composed of polychlorinated biphenyls, is also exploited. The separation requirements for obtaining a given separation goal are investigated and the relevance of the IM type in determining the overlapping pattern is proved. The basic underlying hypothesis of the present treatment is the stationarity of the component distribution along the chromatogram. Means to check this hypothesis are also reported.

Analysis of complex mixtures recovered from space missions: Statistical approach to the study of Titan atmosphere analogues (tholins)

To study Titan, the largest moon of Saturn, laboratory simulation experiments have been performed to obtain analogues of Titans aerosols (named tholins) using different energy sources. Tholins, which have been demonstrated to represent aerosols in Titans haze layers, are a complex mixture, resulting from the chemical evolution of several hydrocarbons and nitriles. Their chromatographic analysis yields complex chromatograms, which require the use of mathematical procedures to extract from them all the information they contain. Two different chemometric approaches (the Fourier analysis approach and the statistical model of peak overlapping) have been successfully applied to pyrolysis-GC-MS chromatogram of a tholin sample. Fundamental information on the mixtures chemical composition (number of components, m) and on the separation system performance (separation efficiency, sigma) can be easily estimated: the excellent correspondence between the data calculated by the two independent procedures proves the reliability of the statistical approaches in characterizing a tholin chromatogram. Moreover, the plot of autocorrelation function contains, in a simplified form, all the information on the retention pattern: retention recursivities can be easily singled out and related to specific molecular structure variations. Therefore, the autocorrelation function (ACF) plot constitutes a simplified fingerprint of the pyrolysis products of tholins, which can be used as a powerful tool to characterize a tholin sample.

Distribution of n-alkanes in the Northern Italy aerosols: data handling of GC-MS signals for homologous series characterization.

The paper describes the characterization of n-alkane homologous series present in PM samples performed by gas chromatography-mass spectrometry analysis. The PM samples were collected in three locations in northern Italy: Milan, a large urban area, Oasi Bine, a rural site far from big city centers, and Alpe San Colombano, a remote, high altitude site in the Alps. They represent different particle sizes (PM(1), PM(2.5), PM(10)) and seasons (summer, fall, and winter). The analyzed samples were characterized in terms of PM total mass, total concentration of C(20)-C(32) n-alkanes and carbon preference index, CPI, to quantify the relative abundance of odd versus even n-alkanes. As alternative to the conventional method based on peak integration, a chemometric approach based on autocovariance function (EACVF) computation was found reliable to characterize the homologous series. In particular two parameters have proven useful chemical markers for tracking the biogenic and anthropogenic origins of n-alkanes: CPI(EACVF) and series %, estimating the % n-alkanes abundance relative to total alkane concentration. The investigated samples display a large variation in the n-alkanes relative abundance: the lowest values (series % = 1-14%) were found in summer and the highest (series % = 24-48%) in winter. In addition, a considerable seasonal variation of CPI(EACVF) values can be identified for all the sampling sites: the CPI(EACVF) values are close to 1 (CPI(EACVF) = 0.8-1.2) in the cold seasons, revealing a strong contribution from anthropogenic emissions, while spreader values (CPI(EACVF) = 0.9-3) were found in the warm season, that is, reflecting a variable contribution from biogenic sources in combination with anthropogenic emissions.

Decoding complex multicomponent chromatograms by fourier analysis

SummaryThe present work discusses the many attributes—classified as observable, intrinsic or hidden—which can be conceived for any complex multicomponent chromatogram. Discussion ensues on how to decode such chromatograms, i.e. determining the intrinsic and/or hidden attributes from those which can be observed. There are two main steps. The first is based on Fourier Analysis (FA) and determines the intrinsic attributes: i.e., the number of single components which can be detected; their distribution over the available chromatographic space and peak capacity. The second evaluates the hidden attributes: i.e., the effects of incomplete separation, the number of peaks created by one or more single components as well as their degree of purity. The hidden attributes can be obtained by applying the theory of Statistical Degree of peak Overlapping (SDO) and the paper goes into the extent to which the SDO step depends on the FA results. In addition, the role Exponential distribution plays as a point of reference for the distribution of both single component peak position interdistances and peak heights is discussed. Finally, a simplified graphical FA procedure is presented and the main achievements in this field are reviewed.

High-performance liquid chromatographic determination of naphthols as 4-aminoantipyrine derivatives : Application to carbaryl

Abstract The high-performance liquid chromatographic determination of 1- and 2-naphthol after derivatization with 4-aminoantipyrine is described. The chromatographic analysis of the reaction mixtures showed two main coloured products for each naphthol. In order to investigate the nature of the reaction products a spectroscopic study ( UV — VIS , IR , NMR ) of the products separated by chromatography was performed. On the more stable 1-naphthol reaction product the quantitative determination of 1-naphthol was performed in the 0.05–10 ppm concentration range. Instability of the 2-naphthol products made their quantitative determination difficult; detection at two different wavelengths (460 and 412 nm) gave a very reliable criterion of qualitative identification. As 1-naphthol is the major degradation product of the insecticide carbaryl, this determination reaction of 1-naphthol was applied to carbaryl. The applicability and performance of the method was checked by determining the carbaryl content in commercial powder formulations and residues in apples.

Relationship between the chromatographic behaviour of dermorphin-related oligopeptides and the composition of the mobile phase in reersed-phase thin-layer chromatography: comparison of extrapolated RF values

Abstract The RT>F values of a series of dermorphin-related oligopeptides were determinded in two reversed-phase thin-layer chromatographic systems, the mobile phase being an aqueous buffer alone or mixed with various amounts of methanol or acetone. The linear relationship between the chromatographic behaviour and the composition of the mobile phase yielded very similar extrapolated RF values at 0% of organic solvent in both systems. This shows that the extrapolated RF values are independent of the nature of the organic solvent. In other words, the extrapolated RF values should be related to the partitioning of the compounds between water and silicone oil in a standard system where all the compounds can be compared.