Giovanni Sacchero

Ion chromatographic separation and on-line cold vapour atomic absorption spectrometric determination of methylmercury, ethylmercury and inorganic mercury

The ion chromatographic separation of methylmercury, ethylmercury and inorganic mercury as cysteine complexes was investigated. The chromatographic apparatus was interfaced with cold vapour atomic absorption spectrometry for detection using an on-line continuous flow cell coupled with a reduction system (sodium tetrahydroborate). The influence of the composition of the eluent (pH, ionic strength, cysteine concentration) and stripping gas flow-rate was investigated. The method was optimized by coupling an on-line preconcentration step. The detection limits, evaluated on 100.0-ml samples, were 2, 10 and 4 ng for Hg, CH3Hg and C2H5Hg, respectively. The method was applied to synthetic mixtures and natural samples (tap water) and furnished satisfactory results.

Comparison of prediction power between theoretical and neural-network models in ion-interaction chromatography

The separation by ion-interaction chromatography (IIC) of metal complexes having single and double charges has been studied in order to compare the prediction power of soft (neural-network) and hard modelling (IIC equation). The two approaches have been used to model the retention behaviour as a function of the composition of the mobile phase. With ion-interaction mobile phases, the parameters involved included the concentrations of ion-interaction reagent, organic modifier and ionic strength. From a set of 69 experimental design points (the different mobile phase compositions at which capacity factors are measured), one test set of ten design points and ten training sets, containing from 59 to 11 design points, have been extracted. Chromatographic and chemometric considerations for the selection of the data sets and minimum number of observations required have been discussed. The study showed that the IIC equation predicted more accurately when few experimental data were available, while a similar prediction power was obtained with both models when the number of data was more than 17. Nevertheless the neural-network accounted for a greater versatility without the need to develop an equation.

Determination of copper, cadmium, iron, manganese, nickel and zinc in Antarctic sea water. Comparison of electrochemical and spectroscopic procedures

Abstract Different procedures for the determination of ultratrace metal ions in Antarctic sea water have been adopted and critically compared. The investigated metal ions were Cd, Cu, Fe, Mn, Ni and Zn. Sea water samples were analysed with adsorptive cathodic stripping voltammetry and with graphite furnace atomic absorption spectroscopy. Different treatments, such as UV irradiation, acidification and on-line sample enrichment were adopted and the results for samples collected in different sites and on a vertical profile were discussed and compared.

Simultaneous determination of methyl-, ethyl-, phenyl- and inorganic mercury by cold vapour atomic absorption spectrometry with on-line chromatographic separation

Abstract A fully automated system for on-line high-performance liquid chromatographic separation, reduction and determination by cold vapour atomic absorption spectrometry (CVAAS) of methyl-, ethyl-, phenyl- and inorganic mercury is described. Reversed-phase chromatography on an ODS column and elution with an acetonitrile-water-ammonium tetramethylenedithiocarbamate buffered mixture was investigated with or without ammonium tetramethylenedithiocarbamate precomplexation. A simple glass flow cell, properly designed as an interface between the chromatographic system and CVAAS, is proposed. The influence of the composition of the eluent, reducing solution and stripping gas flow-rate was investigated and optimized in order to obtain better detection limits. The method, applied to synthetic mixtures and natural samples of tap water furnished satisfactory results. It is shown that, with the on-line preconcentration procedure, sub-ng/ml concentration levels can be determined for all the species considered.

Retention model for the separation of anionic metal-EDTA complexes in ion chromatography

Abstract A retention model is derived for complex anions eluted from an anion-exchange column with multiple ionic eluents containing hydrogencarbonate, carbonate, and hydroxyl species and the sample solution, containing transition metals, anions and complexing ligand. The theory is based on the generalized ion-exchange equilibrium, protonation and complex-formation equilibria. The unknown parameters of chromatographic ion-exchange equilibrium constants for sample and eluent species are determined from the experimental retention data by iterative minimization, using a non-linear regression algorithm. The model was utilized to predict the retention behaviour of CdEDTA2−, CoEDTA2−, MnEDTA2− and NiEDTA2− ions. The capacity factors of complex ions were determined for wide ranges of pH values and eluent concentrations. Good agreement was obtained between the observed and predicted retentions.

On-line preconcentration and ion chromatography of triazine compounds

Abstract An ion chromatographic method was developed for the determination of triazine herbicides in environmental samples. Considering the polar nature of triazines, a cation-exchange column with a multi-mode pellicular packing was used. Optimization of the eluent (organic modifier concentration and ionic strength) is described with reference to the separation, on-line clean-up and preconcentration procedure. Several enrichment materials were evaluated and detection limits below 100 ng/l were achieved with a reversed-phase silica. The determination of triazines in tap water and river water samples was performed with UV detection (220 or 263 mm).

Reversed-Phase Ion-Interaction Chromatography of Metal Ions by EDTA Precomplexation

SummaryConditions for the isocratic separation by reversed-phase ion-interaction chromatography of Bi(III), Fe(III), Co(III), Ni(II), Cu(II) and Pb(II) chelates with ethylenediaminetetraacetic acid have been studied using UV-Vis detection. Both chromatographic and spectrophotometric conditions for the determination of these metal chelates are discussed including ion-interaction reagent concentration, water/methanol ratio, ionic strength, pH and absorbing wavelengths. Detection limits are particularly satisfactory for Bi(III), Fe(III) and Co(III) chelates.

On-line preconcentration and separation of neutral and charged aromatic compounds by ion interaction chromatography

An ion-interaction based chromatographic procedure was developed for the on-line preconcentration, separation and UV detection of benzene and naphthalene sulphonic derivatives having different charges. The retention behaviour of the species was studied on an octylsilica stationary phase, using cetyltrimethylammonium chloride (CTACl) as ion pair reagent and methanol as organic modifier in the presence of sodium chloride. The effect of CTACl, CH3OH and NaCl concentrations was evaluated for the separation of neutral compounds (benzene and naphthalene), monosulphonic acids (benzenesulphonic, toluene-4-sulphonic and 1-naphthalenesulphonic acids), disulphonic acids (benzene-1,3-disulphonic and naphthalene-1,5-disulphonic acids) and naphthalene-1,3,6-trisulphonic acid. The preconcentration recoveries, after the optimization of CTACl concentration added to the sample, made it possible to reduce the detection limits from ppm to sub-ppb levels for some analytes.

Distribution of minor and trace metals in Carezza Lake (Antarctica) ecosystem

Abstract This paper reports the distribution of a series of metals in natural samples collected at Carezza Lake in Antarctica, during the Italian Expedition in the austral summer 1989/90. The considered elements are: water, sediments and soil sampled from the surroundings of the lake and algae. The determination of the total concentration of the following metals was performed: Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Zn. In addition, for sediment and soil samples, a speciation study was performed for some metals, namely Cd, Co, Cr, Cu, Fe, Mn, Ni, Zn, using the Tessier procedure.

Chromatographic behaviour of triazine compounds

A comparative study was made of the chromatographic behaviour of eight 1,3,5-triazine compounds, including Cl-triazines and S-triazines (Ametryne, Atrazine, Cyanazine, Prometryne, Propazine, Simazine, Terbutryne, Terbutylazine). The techniques investigated included liquid-liquid partitioning and ion interaction chromatography with UV detection. Capacity factors are discussed as a function of mobile phase parameters: pH, ionic strength and organic modifier and ion interaction reagent concentrations.