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Francesco Dondi

Publications and source records attributed to Francesco Dondi.

At least 19 recordsLinked to original sources
PubMed2005

Adsorption equilibria of benzodiazepines on a hybrid polymeric chiral stationary phase.

The chromatographic behavior of a series of racemic benzodiazepines was evaluated under linear and nonlinear conditions on a new hybrid polymeric (DACH-ACR) chiral stationary phase (CSP). Differently substituted benzodiazepines were employed as probes to make hypotheses concerning possible molecular interaction mechanisms originating between target compounds and active sites on the CSP. Hydrogen bonds were found to be pivotal for chromatographic retention and chiral selectivity. The competitive effect from a mobile-phase (MP) modifier able to interact with the CSP through H-bonds was investigated. The performance of the polymeric DACH-ACR CSP for preparative purposes was also evaluated. The competitive adsorption isotherms of two benzodiazepines, lorazepam and temazepam, were measured at different MP compositions through the so-called inverse method. The adsorption data were fitted with a competitive bi-Langmuir adsorption isotherm. Enantiomeric separations under nonlinear conditions were modeled by using the equilibrium dispersive (ED) model of chromatography. Theoretical overloaded band profiles (obtained by solving the system of partial differential equations described by the ED model) matched, in a significantly accurate way, the profiles experimentally measured.

Adsorption↗
PubMed2005

Stochastic theory of size exclusion chromatography: peak shape analysis on single columns.

The stochastic theory of size exclusion chromatography (SEC) was applied to analyze the peak shape of chromatograms obtained with a wide range of polystyrene standards on various columns. The columns were packed with stationary phases of different pore sizes. The stochastic-dispersive model of SEC results in a peak shape model that fits well the symmetrical and asymmetrical peaks observed in SEC. From the peak shape parameters obtained after nonlinear parameter estimation, information can be gained regarding the fundamental characteristics of the size exclusion process. When a series of polymer standards are analyzed on one column-in a manner similar to other methods of inverse chromatography-the stationary phase can be characterized. The dependence of the ingress and the egress processes on the relative size of the macromolecule to the pore size was determined. We found that for small molecules the selectivity in SEC arises from the ingress process, while when the size of the macromolecule is comparable to that of the pore-i.e., close to the exclusion limit-the egress process will also strongly affect the selectivity.

Journal Article↗
PubMed2005

Single-molecule observation and chromatography unified by Lévy process representation.

A renewed stochastic model of chromatography is proposed able to establish a conceptual link between the single-molecule dynamics observations in a given chromatographic system and chromatographic experiment results in the same media. The chromatographic peak is expressed through its Fourier transform as a function of the experimental sorption time distribution. The pertinent numerical procedure necessary for obtaining the chromatographic peak is described, and the numerical programming code is given. Two types of cases were considered, the first one where the sole discrete sorption time distribution is available, and the second one where the adsorption mechanism is made of a mixture of continuous and discrete sorption time distributions. The method is applied to experimental data found in the literature by determining typical chromatographic peak shapes on the basis of the experimental interface adsorption data. This renewed stochastic approach is based on the so-called Levy canonical description of stochastic processes and appears to be the most general basis for handling separation processes from a stochastic point of view.

Journal Article↗
PubMed2005

Spot overlapping in two-dimensional maps: a serious problem ignored for much too long.

In the analysis of a neuroblastoma xenograft implanted in mice using two-dimensional maps, some 85 proteins were found to be up- or down-regulated (out of a total of 264 detected by a medium-sensitivity colloidal Coomassie stain). When these spots were eluted and analysed by mass spectrometry in a quadrupole time of flight mass spectrometer, a number of spots were found to be envelopes of different polypeptide chains. Out of a total of 74 proteins identified, 52 (71%) were found to be singlets, 14 (19%) were doublets, 6 (8%) were triplets, 1 was a quadruplet and 1 a quintuplet. Analysis of the DeltapI and DeltaMr of all species contained in a single gel segment eluted helped point out potential errors in protein identification. This was a unique case, in that very minute bioptic sample loads were applied to the gel. In normal cases, where sample loads of ca. 1 mg of total protein are applied and typically at least 1000 spots are visualised, the singlets will be the minority, rarely exceeding 30% of all spots analysed. The experimental data on the abundance of overlapping spots were in excellent agreement with theoretical data calculated on the basis of the statistical theory of spot overlapping, originally proposed by Davis and further developed by some of the authors. Ways and means for minimizing spot overlap and visualising a greater number of spots in a two-dimensional map are discussed.

Adrenal Gland Neoplasms↗
PubMed2005

Validation of a human immunoturbidimetric assay to measure canine albumin in urine and cerebrospinal fluid.

The aim of this study was to validate an automated immunoturbidimetric assay used to quantify human albumin in urine and to accurately measure canine albumin concentrations in both urine and cerebrospinal fluid. The partial homology existing between human and canine albumin limited the accuracy of the human assays in measuring canine albumin without method modifications. Thus, the assay was modified by calibrating the analyzer with calibrators made in the laboratory containing known concentrations of canine albumin. To prepare the set of calibrators, the albumin concentration of pooled sera of healthy dogs was assessed in 5 replicates using the BromocresolGreen assay. Pooled samples were aliquoted and serially diluted to obtain the expected concentrations of albumin (0.5, 1, 5, 13, and 30 mg/dl) for establishing the canine calibration curve. Thereafter, the performance was assessed by analyzing canine urine and CSF The modified assay accurately quantified canine albumin in both specimens, as indicated by the following. Intra- and interassay variability was 0.92% and 2.74%, respectively; recovery was 99.66% and 99.07% in urine and 105.02% in CSF No interference was detected when hemolysate and glucose were added to urine. The test was linear within the verified range (0-225 mg/dl). These results demonstrate that the modified human albumin immunoturbidimetric assay can be a useful tool in the veterinary diagnostic laboratory. It is accurate and tends itself to automatization on chemistry analyzers.

Albumins↗
PubMed2005

Correspondence between chromatography, single-molecule dynamics, and equilibrium: a stochastic approach.

We report a detailed study concerning the correspondence between separations by chromatography, dynamic quantities coming from single-molecule measurements at the interfaces, and phase partition equilibrium by using the unifying approach of the stochastic description. The fundamental hypotheses allowing establishing the proper links between the three experimental techniques are discussed, and the full correspondence between the different quantities is determined from basic principles. The expressions of the errors on the retention factor which are intrinsically linked to the separation process, and which arise from peak splitting, peak tailing, stochastic bias, injection step, and number of the analyte molecules, are derived under general conditions and discussed in detail. Reference is made to the growing area of microsystems or nanosystems and chip technology, with numerical examples. How to determine the impact of single-molecule dynamics observations on the chromatographic peak shape of the experimentally observed sorption time distribution and, in general, of the behavior of the species at the stationary phase (surfaces, interfaces) is pointed out.

Journal Article↗
PubMed2004

Programmed field decay thermal field flow fractionation of polymers: a calibration method.

The universal calibration procedure typical of thermal field flow fractionation (ThFFF) under constant thermal field operation was extended to thermal field programming (TFP) operation. The method requires knowledge of the following: (a) the programming function, which only depends on the thermal field decay function, (b) the physicochemical properties of the solvent, and (c) the calibration plot under varying channel cold wall temperatures (T(c)). Two field flow fractionation field programming conditions, with either a constant or a variable in time carrier flow velocity, are exploited. The method is based on determination, for each retention time position, of the average lambda retention value typical of TFP ThFFF. This parameter is then used to obtain the calibration plot (i.e., the molecular weight of the species as a function of the retention time position) by using the programming function and the calibration plot under varying T(c) values. The procedure approximation errors are also derived as a function of the programming type and solute-solvent system. To properly test the procedure, the calibration plot for the system constituted by polystyrene (PS) in cis-trans Decalin was determined, under varying conditions T(c) and thermal gradients, by using a set of monodisperse PS standards of different molecular weights (M). The procedure was first validated by simulation under two typical cases of TFP ThFFF operation. The approximation errors were found acceptable (in the worse cases, the accuracy in M prediction was 3%) and are in agreement with the theory. The procedure was then experimentally validated under varying programming decay function conditions. The reproducibility and accuracy of the M determination are both better than 2%.

Journal Article↗
PubMed2004

Equivalence of the microscopic and macroscopic models of chromatography: stochastic-dispersive versus lumped kinetic model.

The microscopic model of chromatography is a stochastic model that consists of two fundamental processes: (i) the random migration of the molecules in the mobile phase, and (ii) the random adsorption-desorption of molecules on the stationary phase contained in a chromatographic column. The diffusion and drift of the molecules in the mobile phase is described with a simple one-dimensional random walk. The adsorption-desorption process is modeled by a Poisson process that assumes exponential sojourn times of the molecules in both the mobile and the stationary phases. The microscopic, or molecular model of chromatography studied here turns out to be identical to the macroscopic lumped kinetic model of chromatography, whose solution is well known in chromatography. A complete equivalence of the two models is established via the identical expressions they provide for the band profiles.

Chromatography↗
PubMed2004

Decoding two-dimensional complex multicomponent separations by autocovariance function.

A new method for decoding two-dimensional (2D) multicomponent separations based on the use of the 2D Autocovariance function (2D-ACVF) has been developed. Theoretical models of single component (SC) spot distributions in 2D separations, both random and structured, are developed as the basis for a nonlinear estimation of both sample and separation system parameters from experimental 2D separations. The number of SCs, the average spot size, the spot capacity, and the saturation factor can be evaluated in the case of random SC spot patterns. The procedure was validated by extensive numerical simulation under conditions close to those usually found in GC x GC or 2D-polyacrylamid gel electrophoresis of proteins. The worse precision degree was no greater than 10% in the case of maximum spot density. This imprecision was fully accounted for, and it seems acceptable owing to the intrinsic statistical character of the estimation method. Structured multicomponent 2D separations, where SCs are linked by linear relationships, give rise to specific structured patterns in 2D-ACVF plots from which the parameters (phase and frequency) of the structured SC sequences can be evaluated: the study of 2D-ACVF makes it possible to decode multicomponent 2D separation, that is, to determine the number, relative abundance, and structural similarities of the single components. Pertinent expressions of the theoretical 2D-ACVF were derived for simple cases, and a procedure for decoding cases of structured 2D separations was developed and applied. It was shown that 2D separations containing both random and structured patterns of SC spots give rise to 2D-EACVF, which is the superimposition of the two component parts. This feature allows one, in principle, to decode the two components. The relevance of these results for Giddings sample dimensionality and separation dimensionality and their effective experimental evaluation is discussed.

Journal Article↗
PubMed2004

Study of mechanisms of chiral discrimination of amino acids and their derivatives on a teicoplanin-based chiral stationary phase.

The behavior of a series of amino acids and some of their methyl ester hydrochloride, N-acetyl and N-tert-butyloxycarbonyl derivatives has been investigated on a teicoplanin-based chiral stationary phase by changing the chromatographic conditions, namely, the type and amount of mobile phase organic modifier and the ionic strength of the solutions. By using species with significantly different characteristics and chemical reactivity, some general conclusions regarding the chiral recognition process on this kind of stationary phase have been formulated. The importance of the carboxylic moiety for the formation of the complex between enantiomers and the aglycone basket of teicoplanin has been demonstrated via chromatography. Additionally, the increased possibility to make an hydrogen bond between the amidic hydrogen of the acetylated compounds and an amidic group on the stationary phase has been proposed to be pivotal for the stability of the complex aglycone D-enantiomer. Phenomena leading to the exclusion from the chiral stationary phase of one or both enantiomers have been rationalized by considering the ionic interactions between stationary phase, molecules to be separated and the surrounding medium and/or steric hindrance effects. The understanding of some of the observed phenomena may be important for optimizing the performance of the separation on aglycone-based media.

Acetylation↗
PubMed2003

Decoding of complex isothermal chromatograms recovered from space missions. Identification of molecular structure.

A chemometric approach, based on the study of the autocovariance function, is described to study isothermal GC chromatograms of multicomponent mixtures: isothermal GC analysis is the method of choice in space missions since it is, to date, the only method compatible with flight constraints. Isothermal GC chromatograms look inhomogeneous and disordered with peak density decreasing at higher retention times: a time axis transformation is proposed to make retention an homogeneous process so that CH2 addition in terms of an homologous series yields a constant retention increment. The time axis is transformed into a new scale based on the retention times of n-alkanes, as they are the basis of the universal Kovats indices procedure. The order introduced into the chromatogram by retention time linearization can be simply singled out by the experimental autocorrelation function (EACF) plot: if constant inter-distances are repeated in different regions of the chromatogram, well-shaped peaks are evident in the EACF plot. By comparison, with a standard mixture it is possible to identify peaks diagnostic of specific molecular structures: study of the EACF plot provides information on sample chemical composition. The procedure was applied to standard mixtures containing compounds representative of the planetary atmospheres that will be investigated in the near future: in particular, those related to Titan's atmosphere (Cassini-Huygens mission) and cometary's nucleus (Rosetta mission). The employed experimental conditions simulated those applied to GC instruments installed on space probes and landers in space missions. The method was applied to two specific investigations related to space research, i.e., a comparison of retention selectivity of different GC columns and identification of the chemical composition of an unknown mixture.

Chromatography, Gas↗
PubMed2003

Spot overlapping in two-dimensional polyacrylamide gel electrophoresis maps: relevance to proteomics.

Proteomics requires a large-scale, simultaneous separation of proteins from a mixture, assessment of the relative abundance of these molecules, and identification and characterization of each component. In 2-D PAGE separations, the best method of choice for protein analysis, separation of all the proteins present in the sample is still far to be achieved and comigrating proteins in the same spot are in general present. A statistical estimation of the degree of spot overlapping present in a 2-D PAGE separation is here described: for different conditions of spot overcrowding in the map, the degree of overlapping can be quantified in terms of purity degree of each spot or percentage of proteins that will appear in the map as a single spot. A computer simulation approach is described: it is based on the protein separation pattern present in the experimental maps. The results thus obtained are compared to a theoretical model (statistical degree of peak overlapping model) based on random spot position. The described procedures were applied to an experimental reference map of human plasma. The severity of spot overlapping in 2-D PAGE maps is estimated and the influence of different experimental conditions (strip dimension, detector system performance, pI range) is discussed. These informations are useful to quantitatively estimate the degree of error associated with identification and quantitation of each protein and to set-up experimental conditions which will increase resolution and greatly decrease the probability of spot overlapping.

Computer Simulation↗
PubMed2003

Experimental approaches for size-based metal speciation in rivers.

A review of the different methodologies employed to fractionate and characterize riverine suspended particulate matter is presented. The importance of size-based metal speciation is underlined and the possibility of studying it by the Sedimentation Field Flow Fractionation (SdFFF) technique is illustrated. The studies on the metal load in river Suspended Particulate Matter (SPM) performed over the last ten years are critically reviewed focusing on the different methods employed to collect, concentrate and size-fractionate samples. The fact that there is no homogeneity in methods and data collection in this field is underlined. Among the different fractionation techniques, Field Flow Fractionation (FFF) methodologies have proved to be a good approach to study the role of SPM in metal load and transport. The possibility of studying size-based metal speciation using the SdFFF technique is presented and the importance of metal speciation in rivers is underlined.

Environmental Monitoring↗
PubMed2002

Monte Carlo model of nonlinear chromatography: correspondence between the microscopic stochastic model and the macroscopic Thomas kinetic model.

The Monte Carlo model of chromatography is a description of the chromatographic process from a molecular (microscopic) point of view and it is intrinsically based on the stochastic theory of chromatography originally proposed by Giddings and Eyring. The program was previously validated at infinite dilution (i.e., in linear conditions) by some of the authors of the present paper. In this work, it has been further validated under nonlinear conditions. The correspondence between the Monte Carlo model and the well-known Thomas kinetic model (macroscopic model), for which closed-form solutions are available, is demonstrated by comparing Monte Carlo simulations, performed at different loading factors, with the numerical solutions of the Thomas model calculated under the same conditions. In all the cases investigated, the agreement between Monte Carlo simulations and Thomas model results is very satisfactory. Additionally, the exact correspondence between the Thomas kinetic model and Giddings model, when near-infinite dilution conditions are approached, has been demonstrated by calculating the limit of the Thomas model when the loading factor goes to zero. The model was also validated under limit conditions, corresponding to cases of very slow adsorption-desorption kinetics or very short columns. Different hypotheses about the statistical distributions of the random variables "residence time spent by the molecule in mobile and stationary phase' are investigated with the aim to explain their effect on the peak shape and on the efficiency of the separation.

Journal Article↗
PubMed2002

Stochastic theory of size exclusion chromatography by the characteristic function approach.

A general stochastic theory of size exclusion chromatography (SEC) able to account for size dependence on both pore ingress and egress processes, moving zone dispersion and pore size distribution, was developed. The relationship between stochastic-chromatographic and batch equilibrium conditions are discussed and the fundamental role of the 'ergodic' hypothesis in establishing a link between them is emphasized. SEC models are solved by means of the characteristic function method and chromatographic parameters like plate height, peak skewness and excess are derived. The peak shapes are obtained by numerical inversion of the characteristic function under the most general conditions of the exploited models. Separate size effects on pore ingress and pore egress processes are investigated and their effects on both retention selectivity and efficiency are clearly shown. The peak splitting phenomenon and peak tailing due to incomplete sample sorption near to the exclusion limit is discussed. An SEC model for columns with two types of pores is discussed and several effects on retention selectivity and efficiency coming from pore size differences and their relative abundance are singled out. The relevance of moving zone dispersion on separation is investigated. The present approach proves to be general and able to account for more complex SEC conditions such as continuous pore size distributions and mixed retention mechanism.

Chromatography, Gel↗
PubMed2002

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.

Computer Simulation↗
PubMedDate not supplied

Metal content in river suspended particulate matter: data on Po River.

The present study summarizes the last ten years of literature on heavy metal distribution in Suspended Particulate Matter (SPM) and dissolved phase in the Po River (Italy). The work compares different methodologies employed to collect, concentrate and fractionate the samples. The importance of metal speciation as a function of particle size is underlined and two approaches to metal speciation in the colloidal fraction of Po River SPM are presented: Sedimentation Field-Flow Fractionation (SdFFF) and pH-dependent extractions. Finally, emphasis is placed on the need for comparison with a reference "natural background level" of the metal load in Po River particulate matter in order to determine the real human contribution to river pollution. The high values of some trace transition elements, such as Cr and Ni, have been compared with clay sediments around Ferrara and with bricks in historic buildings. The highly comparable natural concentration of these metals in Po fine sedimentary rocks and in historic brick buildings of Ferrara (XII-XVI centuries) can provide information on natural geochemical anomalies.

Environmental Monitoring↗