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This work presents the development of a green paper-based analytical device (Green-PAD) array for pH detection.

In this study, a portable, disposable, and low-cost ionophore-based optical sensor is presented for the monitoring of sulphides and thiols. This sensor was obtained by fixing a classical dye, 5,5′-dithiobis(2-nitrobenzoic acid) (Ellman's reagent, ELL), on an unusual solid support. Indeed, we decided to anchor the dye on the commercial paper sheet known as the “Colour Catcher®” (herein, named under the acronym CC), commonly used in the washing machine to prevent colour run problems. The device obtained can be regarded as an optical sensor since the indicator dye fixed on the solid material changes its spectral properties (colour and hence the UV-vis spectrum) upon contact with the analyte. The relationship between the analyte content and changes in the UV-vis spectrum of the sensor has been provided using partial least squares regression (PLS).

An economic and extremely selective device for Pd(II) determination in very acidic solutions, TazoC-Mar@, is presented. The sensor was prepared via an ion exchange technique of an azoic ligand, (2-(tetrazolylazo)-1,8 dihydroxy naphthalene-3,6,-disulphonic acid), named TazoC, on a Macroporous Strong Anion Exchange Resin, namely Marathon® (Dow Chemical-USA). The TazoC-Mar@ rapidly forms complexes with palladium(II) ions, which give an intense blue colour to the solid phase, even at low pH. The reaction is highly selective and no other metal ions react with the device at this pH. Moreover, the quantification of Pd(II) is reliable when applying partial least squares regression (PLS) to relate the signal to the metal ion concentration. The regression model gives a good fit and correct predictions of Pd(II) concentrations in unknown samples. The method presented here is highly sensitive with an LOD and LOQ equal to 0.2 nM and 0.5 nM, respectively.

Since the emergence of deferiprone as an iron(III) chelating drug, hydroxypyridinones have been intensively explored due to their high affinity for trivalent metal ions and ability to form complexes at physiological pH with low toxicity. For instance, they have been employed as carriers of La(III) in therapy for bone diseases and to remove Gd(III) from Gd-based contrast agents. We believe that a pyridinone-based sensor can be useful for iron(III) monitoring. Herein, we present a novel chelating solid-phase, resulting from the functionalization of a mesoporous silica MCM-41, with the hydroxypyridinone N(3′-aminopropyl)-3-hydroxy-2-methyl-4-pyridinone (AHP) as the active site. The physico-chemical characterization of the new solid-state device, named AHP-MCM41@, demonstrates that the AHP moiety is covalently anchored on the silica surface; the active site concentration was found to be around 0.4 mmol g−1. Furthermore, its sorption of Fe(III) from aqueous solution is rather rapid. The soluble AHP forms a rich variety of complexes with iron(III), which is typical of all analogous O,O donor ligands, and is dominated by M : L = 1 : 3 complexes. Could complexes with such high stoichiometry can be retained in the solid phase? The answer is yes. The existence of these different species in the solid phase is evidenced by the sorption isotherm results and from sorption experiments as a function of solution pH and also in the presence of a competitive ligand. Furthermore, the existence of complexes in the solid phase was demonstrated via solid vis-spectrophotometry, where these species showed identical colour variations to those formed in solution. Such complexes in the solid phase have never been reported in the literature. Additionally, the intense colour of the solid phase in the presence of iron(III) is promising for naked eye detection.

An optode for Cu(II), Cd(II), Zn(II) and Hg(II) sensing has been designed by immobilization of dithizone on a triacetylcellulose membrane (mem-DTZ). The sorption of the metal ions on the mem-DTZ has been thoroughly characterized, in particular sorption kinetics, sorption isotherms and profiles as a function of the pH have been studied. Methods to assess the concentrations of the cations, both individually and in a mixture, in unknown samples, have been developed. In particular, UV-vis spectra and digital information of pictures taken by using a common desktop scanner, of the mem-DTZ sensor after equilibration with different solutions, were acquired and they were correlated with the concentration of the metal ions in solutions. For the single analyte determination, the RGB parameters of the pictures were subjected to Principal Component Analysis (PCA); otherwise the UV-vis spectra of a mixture of two cations were elaborated by Partial Least Squares (PLS) Regression. The membrane responds to the divalent cations by changing colour reversibly. The response time of the mem-DTZ is about 1 h for Cd(II), Hg(II) and Zn(II), but longer for Cu(II): more than 10 h are required. The linear interval is in the range of about 10−7 to 10−5 M for all metal ions. The limit of detection (LOD) is around 10−6 M for Cu(II), Cd(II) and Hg(II); for Zn(II) a lower LOD of 10−7 M is obtained. The applicability of mem-DTZ to real samples has been proved by analysis of the four metal cations in a certificate material (Sewage Sludge CC136A), white wine, and drinking water samples.

A method for the determination of the total metal ion concentration in samples of unknown composition after separation on a chelating resin was applied to the determination of aluminium(III) concentration in real freshwater samples, using Chelex 100 as a sorbing resin. The method, called chelating resin titration, was previously tested on synthetic samples, and allows also the evaluation of the side reaction coefficient [αM(I)] of the metal ion in the presence of the resin, which is useful for the study of metal speciation. To obtain this information, the sorption equilibria of aluminium(III) on Chelex 100 under the experimental conditions must be exactly known. These equilibria were investigated according to a previously reported method, based on the determination of the sorption curves of aluminium on Chelex 100 from solutions of known composition, sometimes containing chelating substances. It was found that the sorption of aluminium on Chelex 100 takes place by formation of three species, AlL, AlL(OH) and Al(OH)3. The corresponding exchange coefficients were determined. Despite the fact that Chelex 100 sorbs aluminium(III) strongly, it was found that the sorption from fresh waters was not quantitative, which was ascribed to the strong complexation of aluminium in the samples considered. The values of αM(I) of aluminium in some freshwater samples at natural pH and acidified up to pH 3 were determined. They were found to be much higher than those ascribable to hydrolysis or to inorganic and organic ligands present in natural waters, being for instance 1012.1 at pH 7.48 and 107.5 at pH 4.88. A similar determination carried out in a 10–3 mol kg–1 sodium chloride solution containing a known amount of aluminium at pH ≈ 8 gave log αM(I) = 14, completely ascribable to hydrolysis, showing that an accurate evaluation can be obtained by the proposed method.

The synthesis and the physico-chemical characterisation of a novel solid phase, designed for iron(iii) sorption, are presented. The solid (indicated in the following as DFO-SAMMS) is made with a hydroxamate siderophore, the deferoxamine (DFO), covalently bound on a self-assembled monolayer on mesoporous silica (SAMMS). The data demonstrate that the DFO molecules are bound to the solid material, grafted on the surface and do not enter the silica pores. A new one-pot synthesis is presented in which DFO is dissolved in DMSO, and left to react with GPTMS with stirring overnight. In the same mixture, SAMMS is added to get the final product. The optimisation of experimental conditions of this novel one-pot synthesis is presented, with results indicating that a temperature of 90 °C, for the reaction between DFO and GPTMS, and the use of MCM-41 silica are the most convenient conditions. The kinetics of sorption reveals that the iron uptake is relatively fast, around 100 min at pH = 2.5, and from the sorption profile of iron(iii), the estimated capacity of the product obtained under optimized conditions was higher than 0.3 mmol g(-1). The results found in the present research are very promising for application in real biological samples.

New solid-phases for the binding, separation and extraction of perrhenate and pertechnetate (ReO(4)(-) and TcO(4)(-)) from water solutions have been developed from a selective molecular receptor. Host compounds being capable of encapsulating these oxoanions are of great interest. The azacryptand, containing two tripodal tetra-amine subunits covalently linked by p-xylyl spacers, is known to display high affinity for ReO(4)(-) and TcO(4)(-) in water. The syntheses of new solid phases, obtained by fixing the receptor on mesoporous silica MCM-41 and Amberlite CG50 supports, are here described. FT-IR, micro-Raman, elemental analysis (CHN), sorption isotherms, (29)Si MAS NMR, and SEM/EDS were employed for solids characterisation. Promising performances were found for silica derivatives, for which the amount of the receptor fixed on silica ranged from 0.2 to 0.3 mmol g(-1). The perrhenate sorption mechanism was investigated with the aim to select the conditions for application in batch and fixed bed column systems.

A method for determining iodate and iodine(+1) in aqueous solutions is proposed. The assay is similar to a previously described method for the determination of iodide and iodine(0), which were titrated with standard iodate in hydrochloric acid solution. A sample solution made 0.5–1.5 M in hydrochloric acid is titrated with a standard iodide solution and monitored spectrophotometrically at 230 nm. The species involved have strong absorbances that are well differentiated at this wavelength. By combining the two titrations it is possible to resolve any mixture of species of iodine in different oxidation states. The precision of the method (standard deviation) is the same both when determining a single species (IO–3, I+, I2 or I–) and a mixture, and is equal to 2 × 10–7M. Chloride and bromide, even at very high concentrations, do not interfere.

1-(Tetrazolylazo)-2-hydroxynaphthalene-3,6-disulphonic acid (T-azo-R), 2-(tetrazolylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (T-azo-C), 1-(thiazolylazo)-2-hydroxynaphthalene-3,6-disulphonic acid (3,6-disulpho-TAN) and 2-(thiazolylazo)-1,8-dihydroxynaphthalene-3,6-disulphonic acid (TAAC) have been investigated as spectrophotometric reagents for palladium(II). Stable water-soluble complexes are formed, even in 1 M perchloric acid, and at this acidity the considered reagents are specific for palladium(II). A number of donor anions interfere in the palladium(II) determination, mainly by competing with the azo dyes for complexation with the metal ion. The first three reagents were found to form 1:1 (metal to ligand) complexes, while the last forms a 1:2 complex, with a molar absorptivity more than twice that of the others. In all instances the spectra of the complexes are well resolved with respect to those of the free ligands. Concentrations of palladium(II) ranging from 2 × 10–6 to 1.5 × 10–4M can be determined spectrophotometrically. The accuracy (relative difference between the known and the found concentration) is 1% at a concentration of 2 × 10–5M.