Alessio Ceccarini

Ion chromatography characterization of polysaccharides in ancient wall paintings

An analytical procedure for the characterisation of polysaccharides and the identification of plant gums in old polychrome samples is described. The procedure is based on hydrolysis with 2 M trifluoroacetic acid assisted by microwaves (20 min, 120 degrees C, 500 W), clean-up of the hydrolysate by an ion-exchange resin, and analysis by high-performance anion-exchange chromatography with pulsed amperometric detection. Using this method the hydrolysis time was reduced to 20 min and the chromatographic separation of seven monosaccharides (fucose, rhamnose, arabinose, galactose, glucose, mannose, xylose) and two uronic acids (galacturonic and glucuronic) was achieved in 40 min. The whole analytical procedure allows sugar determination in plant gums at picomole levels, with an average recovery of 72% with an RSD of 8% as tested on arabic gum. The analytical procedure was tested with several raw gums, watercolour samples and reference painting specimens prepared according to old recipes at the Opificio delle Pietre Dure of Florence (Italian Ministry of Cultural Heritage, Italy). All the data collected expressed in relative sugar percentage contents were submitted to principal components analysis for gum identification: five groups were spatially separated and this enabled the identification of arabic, tragacanth, karaya, cherry+ghatty, and guar+locust bean gum. Wall painting samples from Macedonian tombs (Greece) of the 4th-3rd Centuries B.C., processed by the suggested method, showed the presence of a complex paint media mainly consisting of tragacanth and fruit tree gums. Moreover, starch had probably been added to plaster as highlighted by the presence of a huge amount of glucose.

Supercritical fluid extraction combined on-line with cold-trap gas chromatography/mass spectrometry

Abstract On-line coupling of a supercritical fluid extraction (SFE) system with a gas chromatography/mass spectrometry (GC/MS) instrumentation was performed by a home-made suitably shaped accumulation cell. This coupling eliminates the effect of CO2 flow on the MS detector, and considerably reduces the effect of high boiling compounds on the Chromatographic efficiency in the determination of organic pollutants in environmental samples. Moreover, it enables multi-step extraction based on the addition of the CO2 modifier directly into the extraction cell. In particular, a three-step extraction of some selected polycyclic hydrocarbons (PAHs) from harbour certified marine sediment reference material was performed at 70 °C extraction temperature, 20 MPa extraction pressure, 400 μl min−1 supercritical CO2 flow for a total extraction time of 15 min (i.e. 5 min for each extraction step), and showed recoveries between 80% and 100% for all PAHs considered with a coefficient of variation of about 10%.

Comparison of sampling bags for the analysis of volatile organic compounds in breath.

Nalophan, Tedlar and Cali-5-Bond polymeric bags were compared to determine the most suitable type for breath sampling and storage when volatile organic compounds are to be determined. Analyses were performed by thermal desorption gas chromatography mass spectrometry. For each bag, the release of contaminants and the chemical stability of a gaseous standard mixture containing eighteen organic compounds, as well as the CO2 partial pressure were assessed. The selected compounds were representative of breath constituents and belonged to different chemical classes (i.e. hydrocarbons, ketones, aldehydes, aromatics, sulfurs and esters). In the case of Nalophan, the influence of the surface-to-volume ratio, related to the bags filling degree, on the chemical stability was also evaluated. Nalophan bags were found to be the most suitable in terms of contaminants released during storage (only 2-methyl-1,3-dioxalane), good sample stability (up to 24 h for both dry and humid samples), and very limited costs (about 1 € for a 20 liter bag). The (film) surface-to-(sample) volume ratio was found to be an important factor affecting the stability of selected compounds, and therefore we recommended to fill the bag completely.

Polychlorobiphenyls in Anctartic matrices

Publisher Summary This chapter discusses the research, which shows that polychlorobiphenyls (PCBs) are present in every environmental matrix from Antarctica, though at very low levels. A very peculiar effect of the pack-ice melting process on the PCB content in sea water is highlighted. The snow/firn depth profile indicates that the amount of PCBs reaching the Antarctica via atmospheric transport is decreased. These data needs to be confirmed and should encourage governments to continue the financial support of such studies, since they are not only very important for a better understanding of the contamination processes in Antarctica, but are also a source of invaluable information on environmental global changes. The chapter also includes an overview on the analytical procedures used for the determination of PCBs in environmental matrices and a presentation of the data relevant to the presence of PCBs in the terrestrial ecosystem. It also emphasizes the results obtained during several Italian expeditions, particularly in the Victoria Land and the Ross Sea.

Analytical quality control for the determination of polychlorobiphenyls in environmental matrices

Analytical quality control procedures for ensuring reliable data in the determination of PCBs in environmental matrices are described. Several extraction procedures of PCBs from sediment samples are critically compared and recovery and reproducibility for PCBs determination in sediment and cod liver oil samples are evaluated. Extraction by 1:1n-hexane/acetone mixture in an ultrasonic bath and by supercritical fluids generally give a quantitative recovery and a coefficient of variation lower than 15%, while extraction by a Soxhlet system does not give such good results and requires much longer extraction times. Certified reference materials available from three international organizations, namely the Standards, Measurements and Testing programme of the European Union, the USA National Institute of Standards and Technology and the National Research Council of Canada were used. Finally, the on-going European Union QUASIMEME programme aimed at improving the analytical quality of marine pollution monitoring measurements of European laboratories is addressed.

Preliminary tests to select operating conditions for the accurate determination of stability constants by cation-exchange chromatography: the Cd2+Cl− and Cd2+NO3− systems

Abstract Ion chromatography (IC) has been demonstrated to be a powerful tool for equilibrium constant determination, related to various cation-ligand systems. Nevertheless, no systematic research has been carried out to develop preliminary checks in order to verify whether the variation in ligand concentration in the eluent at constant ionic strength affects the exchange mechanism for the system of interest in the selected chromatographic column. In this paper, tests are proposed which allow one to determine beforehand the experimental conditions to be used in cation-exchange chromatography, whereby parallel mechanisms of elution (mainly in the reversed-phase mode) are avoided. In this way IC becomes an independent rather than an auxiliary means to obtain accurate βi values. Cd(II)Cl− and Cd(II)NO3− systems were considered and are discussed.

Analysis of priority pollutants in environmental samples by on-line supercritical fluid chromatography cleanup–cryo-trap–gas chromatography–mass spectrometry

Abstract On-line coupling of a supercritical fluid chromatography cleanup system with gas chromatography–mass spectrometry (GC–MS) was performed using a custom-made cryo-trap cell. The cleanup system was based on a high-performance liquid chromatography (HPLC) column packed with about 100 mg of Florisil. This coupling considerably reduces the effect of high boiling compounds on the chromatographic efficiency in the determination of organic pollutants in environmental samples. Moreover, it enables multistep elution from the cleanup column by the addition of a suitable supercritical CO 2 modifier, which was performed automatically. The system was proved for the determination of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls in sediment reference material samples, and in spiked sea-water samples. In particular, a three-step elution of selected PAHs, which were the most retained, from the Florisil column was performed at 40°C and 25 MPa, at a supercritical CO 2 flow of 0.4 ml/min for a total elution time of 10 min. The recovery of all contaminants considered was always better than 75%, with a relative standard deviation of about 15%.

Enhancing the quality of information obtained by a comparison between experimental and deconvolved peak parameters in ion chromatography

Abstract Chromatographic peaks are generally asymmetric owing to extra- and intra-column effects. This implies that the experimental retention time, t R,p , and variance, σ p 2 , do not properly describe the shape of a peak under the experimental conditions used, nor do they allow one to predict how this shape will change when the composition of the eluent is varied. Consequently, some of the conclusions drawn from these experimental parameters may contain an extent of error that cannot be evaluated. This may occur for instance when some of the lower order statistical moments are used to estimate thermodynamic properties related to the solute–eluent–chromatographic column system. The aim of this paper is to test whether and to what extent information can be improved in ion chromatography when the moments estimated by some suitable fitting functions are compared to the experimental ones. The following fitting functions were tested: the exponentially modified Gaussian (EMG) (the peak deconvolution leads to the Gaussian curve which would be obtained in the absence of distortion), the bi-Gaussian (bi-G) (the deconvolution leads to the sum of two half-Gaussians), and the two-Gaussians (2-G) (the deconvolution leads to two Gaussians). The last one is proposed in this paper for the first time. Once we had evaluated how each component of a modern IC chromatograph (namely loop, column, post-column conditioning module and detector) affects the peak shape, the three fitting models were tested: (i) to compute β 1 and β 2 stability constants for the Cd +2 /Cl − system from the measurement of the first-order moments at a variable Cl − concentration and constant ionic strength (0.22). It was found that: β 1 =28.86 (EMG), 28.53 and 28.59 (2-G), 28.99 (bi-G) and β 2 =57.96 (EMG), 59.01 and 58.98 (2-G), 53.92 (bi-G). The β values calculated from the experimental retention times referred to the peak maximum were: β 1 =27.89 and β 2 =64.95; (ii) to evaluate, for the various solutes, the dependence on the first order moment ( m 1 ) of some parameters of the i fitting functions, such as τ (the time constant of the exponential modifier in the EMG), σ i (the square root of peak variance) and the asymmetry a / b (graphically measured as the ratio of the distances of the peak contour from the abscissa of peak maximum, at 0.1 peak height). A linear dependence on m 1 was found for: σ i with a slope which depends on the fitting model used and not on the type of solute; τ and a / b with a slope which depends on the solute type. These findings are of interest: (i) to provide a sound tool for the accurate IC estimate of stability constants based on the Gaussian first order moment computed from the deconvolution of the experimentally distorted peak (ii) to evaluate how the shape of the solute peak changes with m 1 when the shift of the peak along the time (or volume) scale due to variations in the eluent composition can be thermodynamically predicted. In the last case the optimized peak separation conditions, which take the effect of peak shape variation into account, might be more efficiently found.

Multispecies reactive transport modelling of electrokinetic remediation of harbour sediments

We implemented a numerical model to simulate transport of multiple species and geochemical reactions occurring during electrokinetic remediation of metal-contaminated porous media. The main phenomena described by the model were: (1) species transport by diffusion, electromigration and electroosmosis, (2) pH-dependent buffering of H+, (3) adsorption of metals onto particle surfaces, (4) aqueous speciation, (5) formation and dissolution of solid precipitates. The model was applied to simulate the electrokinetic extraction of heavy metals (Pb, Zn and Ni) from marine harbour sediments, characterized by a heterogeneous solid matrix, high buffering capacity and aged pollution. A good agreement was found between simulations of pH, electroosmotic flow and experimental results. The predicted residual metal concentrations in the sediment were also close to experimental profiles for all of the investigated metals. Some removal overestimation was observed in the regions close to the anode, possibly due to the significant metal content bound to residual fraction.

Capillary injection device for in situ pre-concentration of trace elements in graphite furnace-atomic absorption spectrometry☆

Abstract A device for in situ pre-concentration of trace elements in graphite furnace-atomic absorption spectrometry (GF-AAS), which is based on the direct introduction of the sample solution into the furnace by a fused silica capillary, is described. Experimental conditions have been optimized for the determination of several elements at the sub pg/g level with a CV always better than 15%. A deposition yield of approximately 95% was estimated by depositing a solution containing NaCl 0.002 M. A very simple and effective device for handling a sample under contamination-free conditions is also described which allowed a CV less than 10% to be obtained for replicate determinations of Cd in blank samples at 0.4 pg/g. The overall analytical system was validated by recovery studies carried out on standard solutions and spiked snow samples. Measurements were performed at 1, 5 and 50 pg/g, and the error was always lower than 20, 10 and 5%, respectively. The evaluation of the experimental detection limits which ranged in the interval 0.1–4 pg/g is finally discussed.