Maria Pesavento

Analytical methods for determination of free metal ion concentration, labile species fraction and metal complexation capacity of environmental waters: a review.

Different experimental approaches have been suggested in the last few decades to determine metal species in complex matrices of unknown composition as environmental waters. The methods are mainly focused on the determination of single species or groups of species. The more recent developments in trace elements speciation are reviewed focusing on methods for labile and free metal determination. Electrochemical procedures with low detection limit as anodic stripping voltammetry (ASV) and the competing ligand exchange with adsorption cathodic stripping voltammetry (CLE-AdCSV) have been widely employed in metal distribution studies in natural waters. Other electrochemical methods such as stripping chronopotentiometry and AGNES seem to be promising to evaluate the free metal concentration at the low levels of environmental samples. Separation techniques based on ion exchange (IE) and complexing resins (CR), and micro separation methods as the Donnan membrane technique (DMT), diffusive gradients in thin-film gels (DGT) and the permeation liquid membrane (PLM), are among the non-electrochemical methods largely used in this field and reviewed in the text. Under appropriate conditions such techniques make possible the evaluation of free metal ion concentration.

Sorption of metal ions on a weak acid cation-exchange resin containing carboxylic groups

Abstract The sorption properties of a commercial resin containing a carboxylic active group, Amberlite® CG-50, for magnesium, calcium, copper and zinc were investigated on the basis of the Donnan model. It is assumed that the main driving force for the sorption of divalent metal ions is the complexation by the carboxylic groups inside the resin. Under typical batch conditions (large excess of ligand) only the 1:2 complexes are formed for all metal ioas considered, whereas in aqueous solution only 1:1 complexes are reported for calcium and magnesium and the monomeric analogues of the active group of Amberlite® CG-50. The intrinsic complexation constants obtained from the batch experiments agree well with those in aqueous solution. The same holds for the intrinsic complexation constant evaluated from Chromatographic experiments. This confirms some previous results obtained with a chelatteg resin containing an iminodiacetic group, Chelex 100. The values of the complexation constants for the carboxylic groups found with Chelex 100 are in agreement with those found with Amberlite® CG-50.

Solvent impregnated resins containing Cyanex 272. Preparation and application to the extraction and separation of divalent metals

Abstract Impregnated resins containing di-(2,2,4-trimethylpentyl)phosphinic acid (Cyanex 272) were prepared by adsorption of the extractant into Amberlite XAD-2 polymeric adsorbant. The distribution of Cyanex 272 between the aqueous and resin phase was studied as a function of pH and loading of the organophosphorous extractant on the resin. The concentration of organophosphorous compound was determined by ICP. XAD-2-Cyanex 272 impregnated resins were tested for the recovery and separation of Zn(II), Cd(II) and Cu(II) from aqueous solutions. The distribution coefficient of Zn(II), Cd(II) and Cu(II) between the aqueous phase and the resin phase were determined under different conditions. The separation factors between the three metal ions are sufficiently large to allow effective separation of Zn from Cd (100%) and Cu (90%). The selective recovery of Zn(II) from aqueous solutions has been carried out by using SIR as the column stationary phase. The retained metal ions were released from the resin quantitatively by elution with hydrochloric acid solutions at the correct concentration for each metal ion.

An easy way to realize SPR aptasensor: A multimode plastic optical fiber platform for cancer biomarkers detection.

The introduction of new compact systems for sensitive, fast and simplified analysis is currently playing a substantial role in the development of point-of-care solutions aimed to assist both prognosis and diagnosis. Here we report a simple and low cost biosensor based on Surface Plasmon Resonance (SPR) taking advantage of a plastic optical fiber (POF) for the detection of Vascular endothelial growth factor (VEGF), selected as a circulating protein potentially associated with cancer. Our system is based onto two crucial aspects. By one hand, the functional layer which allows the transduction signal is based on DNA aptamers, short oligonucleotide sequences that bind to non-nucleic acid targets with high affinity and specificity. By the other hand, the light guiding structure is based on a POF with a planar gold layer as the sensing region, which is particularly suitable for bioreceptors implementation. The sensor revealed to be really useful in the interface characterization. The developed system is relatively easy to realize and could well address the development of a rapid, portable and low cost diagnostic platform, with a sensitivity in the nanomolar range.

Sorption of protons and metal ions from aqueous solutions by a strong-base anion-exchange resin loaded with sulphonated azo-dyes.

Two sulphonated azo-dyes, which bear a nitrogen donor atom in the diazo group and are known to complex many heavy metal ions in aqueous solution, have been found to be sorbed by a strong-base anion-exchange resin (Dowex 1-X8) simply by ion-exchange. The resin containing the dyes behaves like a chelating resin, able to sorb copper(II) and nickel(II) from aqueous solution, if the proper conditions are chosen. The acidity, ionic composition and volume of the aqueous solution, and the amount and nature of the sorbed ligand are the factors which determine the fraction of metal ion sorbed when the batch technique is used. The experimental results are interpreted by using a model of the resin based on the Donnan equilibrium concept, which allows prediction of the sorption conditions on the basis of some independently determined quantities, such as the protonation and complex formation constants in aqueous solution, and the activity of the counter-ion in the resin phase. The exchange of protons between the resin and the aqueous solution can also be explained with this model.

Solvent-impregnated resins containing di-(2,4,4-trimethylpentyl) phosphinic acid II. Study of the distribution equilibria of Zn(II), Cu(II) and Cd(II)

Abstract The extraction of Zn(II), Cu(II) and Cd(II) from nitrate solutions at 0.1 ionic strength by impregnated resins containing di-(2,4,4-trimethylpentyl)phosphonic acid (HL) has been studied at 25°C. The distribution coefficient of the metal ion was determined as a function of both pH and extractant concentration in the resin phase, and the data were analyzed graphically using the slope analysis method and numerically using the program LETAGROP-DISTR. Analysis of the results showed that the extraction of these metal ions can be explained by the formation of metal complexes in the resin phase with a general composition ML2(HL)q where the value of q depends on the metal. Extractions reactions are proposed and the extraction constants of these reactions are presented. Finally, a comparison between the extraction of Zn(II), Cu(II) and Cd(II) with di-(2,4,4-trimethylpentyl)phosphinic acid sorbed into Amberlite XAD-2 and the extraction using an organic solvent as Isopar H has been made.

Solvent-impregnated resins containing di-(2,4,4-trimethylpentyl) phosphonic acid I. Comparative study of di-(2,4,4-trimethylpentyl)phosphinic acid adsorbed into Amberlite XAD-2 and dissolved in toluene

Abstract Solvent-impregnated resins (SIR) containing di-(2,4,4-trimethylpentyl)phosphinic acid (DTMPPA) were prepared by adsorption of the organophosphorus extractant into Amberlite XAD-2 polymeric macroporous support. The distribution of DTMPPA between the aqueous phase and resin phase was determined as a function of both pH and loading of the organophosphorus extractant on the resin. The distribution ratio of the organophosphorus compound was obtained after determining the total phosphorus concentration in the aqueous phase by coupled plasma atomic emission spectroscopy. The data were analyzed numerically by the program LETAGROP-DISTR, in order to determine the distribution constant K D , the aggregation constant K n , and the acidity constant K a . Moreover, in order to clarify the interactions between the polymeric adsorbent and the extractant, Fourier transform infrared spectroscopy studies have been carried out. Finally the distribution of DTMPPA dissolved in toluene has been compared with its distribution in Amberlite XAD-2.

Determination of the total concentration and speciation of Al(III) in tea infusions.

The aluminium species in different tea infusions were investigated, by determining their stability constants and concentration. This was done for some particular samples using a simple experimental method based on the sorption of aluminium on the strongly sorbing resin Chelex 100, by a batch procedure. From the thermodynamic information obtained it is possible to calculate the concentration of the different species, and in particular that of the free metal ion, which is very important for evaluating the adsorption of aluminium on biological membranes. It was found that aluminium in the tea infusions here considered is present at high total concentration, approximately 0.1 mM, but mainly linked to strong complexes, for instance with side reaction coefficient higher than 10(5.11) at pH 3.95 in one case (tea 1). This could be the reason for the low toxicity of aluminium in tea. These strong complexes were not dissociated even in the presence of Chelex 100. In this case only a limiting value of the reaction coefficient could be evaluated. The presence of the very strong complexes was found in all the tea sample here considered. In two of the considered samples (one black and one green tea) a part of Al(III) was linked to less strong complexes, for example with a reaction coefficient 10(4.14) (tea 2, pH 4.20). The presence in the considered tea infusions of other substances able to complex aluminium was also detected, by the well known ligand titration procedure, at concentration ranging from 0.65 to 3.37 mM in three tea infusions, and at somewhat higher concentration in the case of the ready drink, which was also considered for comparison.

Sorption of divalent metal ions on an iminodiacetic resin from artificial seawater

Abstract The sorption of some bivalent metal ions on the iminodiacetic resin Chelex 100 was examined in artificial seawater as an example of a complex matrix, and in the presence of an organic chelating substance in the aqueous phase. The curves reporting the fraction of sorbed metal ions in function of the solution pH were determined experimentally under different conditions and the exchange coefficients were calculated. The intrinsic complexation constants, which are independent of the conditions, were evaluated on the basis of the Gibbs-Donnan model for the resin and agree with those previously obtained in the case of the sorption of the same metals on Chelex 100 from solutions of simpler composition. In some instances the intrinsic complexation constants were similar to the corresponding complexation constants in aqueous solution, while in other cases they were different, depending on the activity coefficient ratio of the species inside the resin. It has been demonstrated that the method derived from the Gibbs-Donnan model can be used for describing and predicting the sorption equilibria also from complex solutions, if all the equilibria set up in the considered system are known.

Localized Surface Plasmon Resonance with Five-Branched Gold Nanostars in a Plastic Optical Fiber for Bio-Chemical Sensor Implementation

In this paper a refractive index sensor based on localized surface plasmon resonance (LSPR) in a Plastic Optical Fiber (POF), is presented and experimentally tested. LSPR is achieved exploiting five-branched gold nanostars (GNS) obtained using Triton X-100 in a seed-growth synthesis. They have the uncommon feature of three localized surface plasmon resonances. The strongest LSPRs fall in two ranges, one in the 600–900 nm range (LSPR 2) and the other one in the 1,100–1,600 nm range (LSPR 3), both sensible to refractive index changes. Anyway, due to the extremely strong attenuation (>102 dB/m) of the employed POF in the 1,100–1,600 nm range, only LSPR 2 will be exploited for refractive index change measurements, useful for bio-chemical sensing applications, as a proof of principle of the possibility of realizing a compact, low cost and easy-to-use GNS based device.