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There is an increasing interest in determining the concentration of furanic compounds naturally formed in food aqueous matrices, by in situ, fast and low-cost methods. A sensor presenting such characteristics is here proposed, and characterized. It is based on a molecularly imprinted polymer (MIP) as a receptor with electrochemical transduction on a screen printed cell (SPC). The molecularly imprinted polymer has been developed for a particular furanic derivative, 2-furaldehyde (2-FAL). The detection bases on the reduction of 2-FAL selectively adsorbed on the polymer layer in contact with the working electrode. The polymer layer is simply formed by in situ polymerization, directly over the SPC and it was characterized by IR, SEM and electrochemical methods. Even if based on an easy and fast preparation procedure, the layer sufficiently adheres to the cell surface giving a reusable sensor. Square wave voltammetry (SWV) was applied as the signal acquisition method. The sensor performance in aqueous solution (NaCl 0.1 M) was tested, obtaining that the dose-response curve is fitted by the Langmuir adsorption isotherm. The sensitivity, and so the limit of detection, were noticeably improved by a chemometric approach based on the Design of experiment method. (optimized conditions: Estep = 0.03 V, Epulse = 0.066 V, f = 31 s−1). In water solution at pH around neutrality the dynamic range was from about 50 μM to 20 mM. Similar results were obtained for a white wine containing 12% ethanol, which has been considered as a typical example of beverage possibly containing furhaldehydes. The higher limit of quantification can be modulated by the amount of MIP deposited, while the lower detection limit by the conditions of the electrochemical measurement.

Intelligent packaging represents an emerging trend in the food industry, especially for highly perishable foods like milk and dairy products. Despite the apparent simplicity, miniaturized BCP-EVOH@ sensor, made of bromocresol purple (BCP) covalently bound to ethylene-vinyl alcohol (EVOH) copolymer, meets the goal of milk freshness monitoring during chilled storage, allowing both naked-eye evaluation and chemometric-assisted spoilage modelling and measurements.

This work presents a simple, fast, disposable and low-cost colorimetric sensor for the simultaneous detection of Fe(III) and Al(III). It is obtained by fixing a classical dye, Alizarin Red S, on an inert solid support, i.e., a product of the washing powder market known as “Colour Catcher®” (here named under the acronym CC) generally used in the washing machine to prevent colour run problems. The device so obtained is called Aliz-CC@. Fe(III) and Al(III) interaction with the Alizarin Red S-based sensor, generates a change in the adsorption spectra of the fixed dye, allowing to highlight a naked-eye colour change. The relationship between the Fe(III) and Al(III) content and the colour change profiles of the sensor, is provided by using Partial Least Squares regression (PLS).

A wide range of substances is reported in the literature as emerging pollutants. Biomass sorption has been found an effective way to remove these pollutants from wastewaters. In this work the ability of cork for the removal of ofloxacin from aqueous solutions has been evaluated. Cork and ofloxacin have been chosen as representative of biomass and of antibiotics, respectively. Ofloxacin is one of the most used fluoroquinolones, a potent broad spectrum oral antibiotic class. The sorption of ofloxacin by cork has been studied by equilibrium isotherms at three pH values (4, 7 and 9) using cork of two different sizes. The K and Qmax values obtained by fitting the data with Langmuir equation are discussed as a function of pH and cork size. In order to know the variously protonated species of ofloxacin that interact with cork at different pH, a potentiometric–spectrophotometric characterization of the protonation equilibria has been performed. A new spectrophotometric method for the quantitative determination of ofloxacin, based on the formation of colored iron(III) complexes, has been developed.

A large number of new solid phases have been proposed in the literature during the past decade with a large variety of purposes: separation and preconcentration for the solid phase extraction, specific chromatographic applications, assemblies of devices for recognition of a family of substances, sensors for a single species identification. In spite of this variety of materials, their properties are mostly depicted by physical descriptors and operational exchange properties, instead of quantities independent of the experimental conditions. In the present review the methods proposed for the description of the sorption phenomena, from the thermodynamic, kinetic and dynamic point of view, will be critically reviewed, focusing on general methods to describe the sorption that could be used in alternative to descriptive and operational approaches.

The sorption of several metal ions on a solid, iminodiacetic based material, the Empore™ chelating membrane, is considered. Determination of the acid-base properties, kinetic of metal sorption and complexing properties, in solutions with different composition is undertaken. The results are compared with those obtained using the classical iminodiacetic resin Chelex 100 in beads. In particular, Cd(II), Fe(III), Pb(II), and Zn(II) are considered. The Gibbs–Donnan, the usual model we used to explain the protonation and the metal sorption on chelating sorbent, is applied also in the present study. On the other hand, the kinetic models selected to describe our data are the two widely applied for fitting ion-exchange data: the Homogeneous Particle Diffusion Model and the Sharing Core (Shell Progressive) Model. In general no significant differences between membrane and resin are found in the thermodynamic properties, but for some metals the kinetics of the sorption on the membrane is slower.

The sorption of copper(II) on a solid, iminodiacetic based, chelating material, the Empore membrane, in alcoholic solutions is considered. Determination of the acid-base properties, kinetic of metal sorption and complexing properties, in solutions with different percentages of ethanol, ranging from 0 to 40% is undertaken. The results are compared with those obtained using the classical iminodiacetic resin Chelex 100 in beads. No significant differences are found in the thermodynamic properties, but the kinetics of the metal sorption on the membrane is slower and a dependence of the process rate with the alcoholic content is observed. In the present investigation, the detection of copper(II) species both in alcoholic Italian distillate "grappa" and in its intermediate product ("flemma"), is carried out by the Resin Titration (RT) method using, as competitive reagent, the Empore membrane. To validate the procedure, synthetic solutions containing different percentages of ethanol are analysed.

Presented hereafter is the pilot-study of the applicability of resin titration (RT) to mixed solvents in regard to the studies of metal distribution in wines – a beverage that has attracted great attention and that has been extensively studied in the recent years. The RT method of studying the distribution of species is based on the determination of the concentration of metal ions sorbed on the iminodiacetic resin Chelex 100 at different V / w (solution volume/mass of resin). The total metal ion present in the considered solution and the free metal ion are estimated from the titration curves. The method, already applied for water solutions, was tested here in mixed solvent media, at the pH around 3, with known amounts of copper(II) and ligands with different complexing properties. Satisfactory results have been obtained and commented critically. In the application of the RT method, the protonation and the exchange reactions of copper(II) with the considered sorbent were investigated in 12% ethanol, in KCl 0.1 and 1.0 M solutions, according to a well established procedure. Finally, a white grape wine (Riesling) from a winery in Oltrepo Pavese was analyzed with RTs. In the sample obtained before processing the wine, 50% of the total Cu(II) (∼18 μM) was combined with ligands with log α M equal to 3.3; in the final product, the total Cu(II) was 4 μM, almost totally complexed. According to these findings, the ligands accountable for the copper complexation were not the major components in the wine, as they formed considerably weaker complexes.

A molecular imprinted polymer (MIP) membrane for atrazine, not containing macropores, was synthesized and implemented in a potentiometric sensor. It is expected to work like a solid ISE (where the specific carrier are the imprinted sites) the specific carrier being the imprinted site. The active ion is the protonated atrazine, positively charged. To form this species the determination is carried out in acidic solution at pH lower than 1.8, in which atrazine is prevalently monoprotonated. At these conditions the membrane potential increases with atrazine concentration over a wide concentration range (3 × 10 −5 to 1 × 10 −3 M). The slope of the function E versus log c is about 25 mV/decade, showing that the atrazine form sorbed on MIP is the biprotonated one. The detection limit is determined by the relatively high concentration of atrazine released by the membrane in the sample solution at the considered conditions. It seems to be independent of the atrazine concentration in the internal solution of the sensor, but it depends on the acidity of the solution. The response time is less than 10 s and the sensor can be used for more than 2 months without any divergence.

Very stable aluminium complexes may be present in natural waters, which can be detected only using appropriate methods. One of them is the resin titration based on the sorption of aluminium on a strongly sorbing resin, Chelex 100. It was here used to detect strong aluminium complexes, and to characterize them by determining their concentration, and the corresponding stability constant. High and low salinity waters were sampled in different sites in the North of Italy. In all the samples aluminium complexes with high stability constant, up to 10 17.4 M −1 in the less acidic solution, were detected. The stability constant depends mainly on the solution acidity, increasing with increasing pH up to 7. The concentration of the ligands responsible for the strong complexation is similar to that of aluminium (from 0.5 to 1.5 μM), or somewhat lower in the case of estuarine and sea waters. A small fraction of aluminium (from 0% to 2%) in freshwaters, higher in estuarine and sea waters (14% and 10%, respectively), is present in weakly bound forms which could also be the hydrolysis products. The conditional constants of the strong complexes were determined for the different samples examined. They were found to be slightly lower in the case of the high salinity waters, in which a value of 10 16.1 M −1 at pH 7.5 was obtained. This is probably due to the higher ionic strength in marine water, which strongly influences the complexation of trivalent metal ions, as seen for example also in the hydrolysis. It could be deduced that similar substances, but at different concentration, would be responsible for the aluminium complexation in the sea and freshwaters here examined. They could be natural organics like fulvic substances, or better some particular complexing sites in this substances with very high affinity for aluminium.

A competion method is proposed to characterize natural metal complexes present in a high salinity spring water. The competitor is a strong complexing resin containing the iminodiacetic group, Chelex 100. Its sorbing properties towards the metal ions here considered, Cu(II), Mn(II) and Al(III), are well known and could be quantified through K*, the ratio of the concentration of the metal in the resin phase to that of the free metal in solution. It can be calculated for the considered metal ion for the particular experimental conditions. From the fraction of metal experimentally sorbed on the resin it is possible to obtain information about the distribution of the metal in the original water solution. Two different methods are proposed. In the resin titration (RT), different volumes of sample are treated with the same amount of resin. RT allows to determine the total metal concentration and the reaction coefficient of that metal in solution. In the ligand titration (LT), the free metal is added stepwise into the original sample, and the ligand concentration and the complexation constant are determined. This was done by the Ruzic linearization method, modified to take unto account the variation of the pH of the solution. Also the data from RT were elaborated by the modified Ruzic linearization. The study of metal ions distribution among different chemical species by the combined methods is discussed in detail. The three metal ions in the considered high salinity water were found to be mainly combined in complexes with high complexation constant. The concentration of the strong ligands involved was near to that of the metals.

Sorption mechanism of bivalent metal ions on a weak cationic resin containing the carboxylic group is studied. The Gibbs-Donnan model is used to describe and then to predict the sorption through the determination of the intrinsic complexation constants. These quantities characterize the sorption being independent of experimental conditions. They are determined according to a well established procedure and using a recently proposed iterative method for calculation of counter ion concentration in the resin phase. Sorption mechanisms are also studied adding appropriate soluble ligands whose complexing properties are exactly known to the solution containing the resin and the metal ion. Competing with the resin for the complexation of the metal, they shift the sorption curve to higher pH and often this allows detecting other complexes between the metal and the resin. In this way for Mn(II), besides the 1:1 complex formed in the more acidic solution, with logbeta(110)=-4.55, the complex ML(2), characterized by logbeta(120)=-9.80, is found; for Cd(II), besides the ML complex, with logbeta(110)=-3.01, at pH higher than 7, the specie MLOH with logbeta(11-1)=-8.28. For Cu(II) the complex ML(2) is detected, confirming previous findings, with logbeta(120)=-7.24. In the presence of two different ligands, sulphosalicylic and malonic acid, a different complex, ML(2)OH, is identified, with the same intrinsic complexation constant for the two ligands, logbeta(12-1)=-13.35. As expected from the model, the intrinsic complexation constants, especially for the 1:1 complex, are in a good agreement with the complexation constants of acetic acid.

The intrinsic protonation and complexation constants of an ion-exchange complexing resin, previously determined in condition of trace metal ions on the basis of the Gibbs–Donnan model of ion-exchange resins, were here used to evaluate the concentration of metal ions sorbed on the resin when the metal ion is in excess. The resin considered was a commercial one, containing carboxylic groups at a concentration of 10 mmol g−1 of dry resin. Metal ions complexable by the active groups present in the resin phase, i.e. alkaline earth metals and cadmium(II), were investigated, together with a not complexable metal ion, sodium, which enters in the resin phase only by diffusion and ion-exchange. The calculation method is an iterative one, taking into account the diffusion and ion-exchange in the case of the not complexable metals, and the complexation in the case of the complexable metal ions. The concentration of metals in the resin phase calculated by the proposed procedure was compared with that obtained experimentally in some representative solutions at different composition and acidity. The agreement was acceptable, showing that the intrinsic complexation constants are of help not only in conditions of trace metal, but also for evaluations at completely different conditions. In the case of complexable metal ions it was shown that the complexation in the resin phase is the most important sorption mechanism, even if ion-exchange takes place at high acidity, when the complexation is negligible.

A chelating resin containing iminodiacetic groups, Chelex 100 which is often employed for sorbing metal ions from complex matrices, was used for separating and preconcentrating heavy metal ions from seawater samples. The resin titration method was applied for determining the total concentration. The experimental procedure consists of measuring the concentration of the metal sorbed on Chelex 100 from solutions with different ratios volume of aqueous phase/amount of resin. The total metal ion concentration is obtained from the experimental data by a model for the sorption on the resin, the parameters of which are obtained by a non-linear regression procedure. In this way not only the total metal ion concentration can be determined, but also the side reaction coefficient α M(I) , if the sorption equilibria of the considered metal ion on the resin are exactly known, as is the case of Chelex 100 considered here. The resin titration with Chelex 100 was utilized for determining the total metal ion concentration in certified seawater samples and real samples from the Ligurian Sea. It allowed the simultaneous determination of the total concentration of manganese(II), cadmium(II), nickel(II) and copper(II), in acceptable agreement with the certified values. Moreover, the side reaction coefficients of some complex species could be evaluated. They were very high, and strongly dependent on the acidity of the sample solution. For instance, values varying from 10 9 to 10 11 were obtained for copper (II) in the different samples considered, at pH around 7. Chelex 100 is such a strong sorbing substance that it is able to compete with the stable complexes for the combination with the heavy metal ions considered here.

A macroporous resin containing iminodiacetic groups (Lewatit) was investigated for its sorption properties towards proton and nickel(II) and cadmium(II). Different compositions of the aqueous phase, and different temperatures were examined. The stoichiometry, the exchange coefficients and the intrinsic constants of the sorption equilibria were obtained from the experimental data by using the Gibbs-Donnan model for the ion exchange resin. The intrinsic constants were found to be independent of the composition of the solution, so that they were used for characterizing the sorption equilibria. While the first intrinsic protonation constant of the active groups in the resin was found to depend on the temperature, the second one was independent. The sorption equilibrium of nickel in the resin was different from that of cadmium, being ascribable respectively to the formation of the complexes NiL and Cd(HL)(2). inside the resin. Their intrinsic complexation constants were found to be 10(-1.84) and 10(-3.64) at 25 degrees C. Compared to those of another resin with the same active groups, but not macroporous, they are higher. The dependence of the intrinsic constant on the temperature was also different for the two metals, allowing to evaluate a DeltaH degrees of +30.9 and of +13.7 kJ mol(-1) respectively. When a comparison is possible, these values are near to those in aqueous solution for the complexation with ligands of similar structure. These results can be used to achieve metal ion separation based on temperature variations.

The sorption properties of the strong anion exchange resin AG1X8 towards aluminium(III) were investigated in view of the study of the speciation of this metal ion in drinking waters. This was done by determining the side reaction coefficients of the metal ion in the sample solution in the presence of the resin. It was found that aluminium(III) is sorbed on AG1X8 by the formation of Al(OH)3 and Al(OH)−4. The exchange coefficients were determined at different conditions and the intrinsic complexation constants were evaluated on the basis of the Gibbs–Donnan model. From the exchange coefficients the ratio of metal ion sorbed on the resin to the free metal ion in solution, K* was evaluated. It is a measure of the sorbing properties of a resin towards a metal ion at a given pH. AG1X8 was used for the determination of total aluminium(III) concentration in drinking water samples by the resin titration (RT) method at pH 7.5 and 6.2. In the first case the total concentration obtained by RT was equal to that determined directly, showing that all aluminium is either quantitatively sorbed or in equilibrium with AG1X8. The side reaction coefficient αM(I) was evaluated to be around 1012 in the considered drinking water samples at this pH. Not any aluminium(III) was sorbed on AG1X8 from the considered drinking water samples at pH=6.2 suggesting that aluminium is present here as species with αM(I)>107. These results were compared with those obtained using Chelex 100, which is able to sorb aluminium(III) also at pH 6.2. More information about the speciation of aluminium can be obtained by comparing the results from two different sorbing resins.

The Gibbs-Donnan model for ion-exchange resins is used to describe and predict the sorption equilibria of metal ions on chelating resins. These are characterized by their intrinsic complexation constants, which, according to thel model, are related to the complexation constants in solution with ligands having structure similar to that of the active groups in the resin. The intrinsic complexation constants are independent of the experimental conditions, for instance the composition of the solution phase. The model is applied to two different kind of chelating resins: a strong anion exchanger loaded with sulfonated azo dyes, and a weak cation exchanger with iminodiacetic groups (Chelex 100) covalently linked to the mainframe. In most cases the complexation inside the resin exactly corresponds to that in aqueous solution, while sometimes the formation of 1-to-2 complexes is promoted inside the resin. In any case the intrinsic complexation constants allow us to evaluate the exchange coefficients, holding at the particular conditions, by the Gibbs-Donnan model. Thus the sorption and elution of a metal ion by a batch procedure can be predicted. A particular application is described, which is useful in the field of analytical chemistry. It is the determination of total and free metal-ion concentration in an aqueous solution of unknown composition, at very low concentration of metal. This also is made possible by the knowledge of the exchange coefficients at the particular conditions.

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.

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.

The sorption of a number of metal ions on the strong-base resin AG 1 × 8 containing the azo-dye Chromotrope 2B has been studied using conventional analytical methods. While lead, cadmium, zinc and magnesium are not sorbed, copper, lanthanum and nickel are. The sorption of nickel was unexpected because complexation in water is negligible. In the resin phase a 1:2 complex was found. For copper both the 1:1 and 1:2 complexes are formed depending on the ligand concentration in the resin. Evidently, the high ligand concentration in the resin promotes the formation of the 1:2 complex. For lanthanum also 1:1 and 1:2 complexes are formed. The experimentally determined extraction coefficients can be related to the intrinsic formation constants with the aid of the Donnan equilibrium. A good agreement is found for the 1:1 complexes of copper and lanthanum, but not for the 1:2 complex of lanthanum, probably due to large differences in the activity coefficients.

The protonation coefficients of three poly(amido-amino acid) resins (GLY, ALA, GABA) and of one poly(amido-amine) resin (RN2C4) were determined at 25°C, in sodium chloride and sodium sulphate aqueous solutions. The results can be interpreted on the basis of the existence of a Donnan potential at the interface resin-solution, due to the fact that all the ionic species, excepted those which are permanently linked to the backbone of the resin, are free to diffuse between the two phases. The importance of the activity coefficients inside and outside the resin phase is pointed out. The calculated intrinsic protonation constants are in good agreement with the protonation constants of the proper monomeric models.

The method is based on reduction of total iodine (10 −7 −10 −5 M), to iodide with sulphite in acidic solution. The excess of sulphur dioxide is removed by bubbling with nitrogen, and the resulting solution is titrated spectrophotometrically with a standard solution of iodate, the absorbance being measured at 230 nm. Some Italian table salts, iodized or common, were analyzed for their iodide and total iodine content.