Angelo Antonio D'Archivio

Comparison of different sorbents for multiresidue solid-phase extraction of 16 pesticides from groundwater coupled with high-performance liquid chromatography

A procedure based on solid-phase extraction (SPE) followed by high-performance liquid chromatography (HPLC) with diode array detection has been developed for the simultaneous analysis of 16 widely used pesticides in groundwater samples. The compounds analysed were: aldicarb, atrazine, desethylatrazine, desysopropylatrazine, carbofuran, 2,4-D, dicloran, fenitrothion, iprodione, linuron, metalaxyl, metazachlor, phenmedipham, procymidone, simazine and vinclozolin. Five different SPE sorbents, C(18) bonded silica (Isolute SPE C18 (EC)), graphitised carbon black (Superclean Envi-Carb), highly cross-linked polystyrene-divinylbenzene (Lichrolut EN), divinylbenzene-N-vinylpyrrolidone (Oasis HLB) and surface modified styrene-divinylbenzene (Strata X), were compared. HPLC separation and quantification of the selected pesticides was carried out under isocratic conditions by means of a new reversed-phase column (Gemini from Phenomenex) based on C(18) bonded to organic-silica particles. Oasis HLB and Strata X provided the best results in the preconcentration of 1-l samples, yielding average recoveries higher than 70%, except for phenmedipham that rapidly degrades in groundwater. Detection limits of the target pesticides provided by the proposed SPE-HPLC procedure were between 0.003 and 0.04microg l(-1).

Polybenzimidazole as a promising support for metal catalysis: morphology and molecular accessibility in the dry and swollen state

Polybenzimidazole (PBI) in beaded form (250-500 microm) has been characterized in the dry state by scanning electron microscopy (SEM), BET, and nitrogen porosimetry. In the swollen state, it has been characterized by inverse steric exclusion chromatography (ISEC) in tetrahydrofuran, toluene, and water, by ESR of TEMPONE (2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine), and pulse field gradient spin echo (PGSE) NMR spectroscopy, toluene, in tetrahydrofuran, ethanol and water. The dry-state results are in good agreement with the ISEC results obtained in tetrahydrofuran, toluene, and water with regard to the 40-80 nm macroporosity. The swelling-dependent surface area and pore volume detected by ISEC in toluene and water reveal the amphiphilic nature of PBI.

Photocatalytic degradation of linuron in aqueous suspensions of TiO2

The photocatalytic degradation of linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea), a widely used herbicide and potential environmental contaminant, in irradiated titanium dioxide aqueous suspensions is investigated. The photocatalytic performance of two nano-sized materials prepared by a sol–gel process, and the influence on the degradation rate of some operational parameters, such as catalyst amount, pH of the medium and hydrogen peroxide concentration, are evaluated. Within the range of the explored experimental conditions, degradation of linuron in an aqueous suspension of TiO2 at mg l−1 contamination levels is described by a pseudo-first-order kinetic model, the apparent half-life time of the herbicide being about 30 min in optimal conditions. Based on the evolution of total organic carbon and the fate of inorganic species, the disappearance of linuron seems to be accompanied by its almost quantitative mineralization.

Metal palladium supported on amphiphilic microporous synthetic organic supports. Part II. Catalytic investigations

Abstract Two sets of resin-supported Pd(0) catalysts were compared in the hydrogenation of cyclohexene in methanol, under ambient conditions. Two lightly crosslinked poly-{styrene/2-methacryloxyethylsulfonic acid/methylenebisacrylamide} with different degrees of crosslinking (1 and 3 mol%), have been used as catalyst supports. Two catalysts with different palladium loadings (0.22 and 2.2 wt%) have been prepared from each support. When the size of the particles was relatively small, the catalysts with 2.2% and 0.22% Pd were almost equally active with respect to the amount of palladium in the reaction mixture. In contrast, when larger catalyst particles were used, catalysts with 2.2% metal produced conversion profiles typical of diffusion-controlled regimes (productivity decreased with increasing crosslinking). These catalysts were characterised by combined ESR and static gradient spin echo NMR spectrometries, which have provided information about molecular motion inside the polymer networks.

Development of molecularly imprinted polymeric nanofibers by electrospinning and applications to pesticide adsorption

Novel polystyrene-based molecularly imprinted polymer nanofibers were synthesized through the electrospinning technique. The molecularly imprinted polymers were prepared using a non-covalent approach and atrazine as template. For comparison, nonimprinted polymer nanofibers were also synthesized. The morphology of the synthesized nanofibers was characterized using scanning electron microscopy. The adsorption of pesticides, atrazine, atrazine desisopropyl, atraton, carboxin, linuron, and chlorpyrifos was studied under equilibrium (batch) conditions. To describe the adsorption capability of the synthesized polymers, Langmuir and Freundlich models were used. The Freundlich model provided a better mathematical approximation of the sorption characteristic for polymers nanofibers. To evaluate the adsorption capacity in the presence of interferents experiments on river water samples spiked with a mixture of six pesticides were also performed. The results obtained for the highest concentration levels investigated, show a greater amount of pesticide adsorbed on molecularly imprinted polymers and non-imprinted polymers compared to those obtained using commercial stationary phases used as reference.

Metal ion implantation onto acidic resins upon reaction of metal acetates and carbamates: Part I. Synthetic results

Abstract Moderately cross-linked gel-type resins bearing –SO3H, –COOH and –OH groups undergo facile metallation with PdII, CuII and NiII acetates with concomitant release of acetic acid. Successful and facile metallation is also observed upon reaction with PdII, CuII and NiII carbamates.

Artificial neural network modelling of retention of pesticides in various octadecylsiloxane-bonded reversed-phase columns and water-acetonitrile mobile phase.

Previously, retention of 26 pesticides in the reversed-phase column Gemini (Phenomenex) and water-acetonitrile mobile phase was modelled using a feed-forward artificial neural network (ANN) learned by error back-propagation, accounting for both the effect of solute structure and mobile phase composition. To this end, logK(ow) of solutes and four quantum chemical molecular descriptors (the dipole moment, the mean polarizability, the anisotropy of the polarizability and an hydrogen-bonding descriptor based on the atomic charges located on the acid and basic functional groups) and acetonitrile % (v/v) in the eluent (%ACN) were used as ANN inputs. The above ANN-based approach is here tested on further five similar octadecylsiloxane-bonded columns in water-acetonitrile mobile phase within the %ACN range 30-70%. A quite good predictive performance evaluated on three external solutes in the whole %ACN range is observed, prediction errors being lower than +/-0.1 log k units or slightly higher although still within +/-0.15 log k units. On the other hand, multilinear regression used in place of ANN provides a more diffuse and non-uniform residual distribution for all the investigated columns. ANN multiple-column retention prediction is attempted by adding to the above variables a column descriptor defined as the average retention of calibration solutes extrapolated to 100% water. This more general model is built using 16 solutes and five 5-microm columns in calibration, while its predictive performance is tested on the remaining 10 compounds. Under these conditions, prediction errors are generally within +/-0.2 log k units regardless of the kind of column. The possibility of cross-column prediction is evaluated by column leave-one-out cross-validation within the five 5-microm stationary phases and on a 4-microm external column. This analysis reveals that accuracy of retention prediction for unknown solutes in unknown columns is acceptable provided that the external column is not very dissimilar to those used in calibration.

Metal palladium dispersed inside macroporous ion-exchange resins: rotational and translational mobility inside the polymer network

Abstract Commercial macroporous strongly acidic ion-exchange resin (Bayer UCP 118) in its acidic and Na + forms and a resin/Pd composite were investigated by means of electron spin resonance (ESR) and pulse field gradient spin echo-nuclear magnetic resonance (PGSE-NMR) techniques, to determine their molecular accessibility to 2,2,6,6-tetramethyl-4-oxo-1-oxypiperidine (TEMPONE ) dissolved in water and the molecular mobility of both TEMPONE and water inside their accessible domains. The paramagnetic probe and water itself occupy both the micro- and macroporous domains of the resin particles, among which a rapid exchange is observed.

An ESR and PGSE-NMR evaluation of the molecular accessibility of poly(vinyl alcohol) hydrogels

Abstract Electron spin resonance spectroscopy (ESR) and pulsed-gradient-spin-echo nuclear magnetic resonance (PGSE-NMR) measurements on poly(vinyl alcohol) (PVA) hydrogels reveal that nanostructure is not appreciably affected by the number of freezing–thawing cycles.

Conformational Changes at the Active Site of Pantetheine Hydrolase During Denaturation by Guanidine Hydrochloride

Conformational changes at the active site of pantetheine hydrolase (EC3.5.1.-) during guanidine hydrochloride (GndHCl) denaturation were investigated by UV and circular dichroism spectroscopy and by electron spin resonance spectroscopy, following the spectral behaviour of the nitroxide radicals (N- (1- oxyl - 2,2,5,5, -tetramethyl-3-pyrrolidinyl) iodacetamide) covalently linked to the two active site cysteine residues. At low denaturant concentrations (0.2 M) no conformational changes may be observed, whereas the catalytic activity, is strongly affected. The results indicate that the active site of pantetheine hydrolase is labile and unfolds under conditions in which no global tertiary struscture modifications can be observed.