Search

This paper presents an overview of the recent applications of molecularly imprinted polymers (MIPs) to sample preparation. The review is thought to cover analytical procedures for extraction of contaminants (mainly illegal/noxious organic compounds) from food and environmental matrices, with a particular focus on the various pre-concentration/cleanup techniques, that is offline and online solid-phase extraction (SPE), dispersive SPE (d-SPE), magnetic SPE (MSPE), solid-phase microextraction (SPME) and stir-bar sorptive extraction (SBSE), applied before instrumental quantification. The selectivity and extraction efficiency of MIP-based sorbent phases are critically discussed, also in relation to the physical-chemical properties resulting from the synthetic procedures. A variety of molecularly imprinted sorbents is presented, including hybrid composites embedding carbon nanomaterials and ionic liquids. The analytical performance of MIP materials in sample preparation is commented as function of the complexity of the matrix, and it is compared to that exhibited by (commercial) aspecific and/or immunosorbent phases.

The preparation, characterization and analytical applications of gold electrodes modified with omega-mercapto alkyl/aryl sulfonates are described. The devices resulted effective for the determination of free and labile Pb(II) in water samples by anodic stripping voltammetry (E(dep) = -600 mV) and in particular 2-mercaptobenzimidazole-5-sulfonate (MBIS) offered the best performances with detection limit of 0.4 microg L(-1). Quantitative stripping of Pb from the electrode surface during the anodic scan, is obtained using sodium citrate buffer (pH = 9.0) as supporting electrolyte. Natural waters were analysed by standard addition method with good recoveries (mean percentage = 97%); no fouling effects due to humic acids or other organic constituents were observed in the reported conditions.

d , l -Penicillamine and thiodimethylglyoxime (TDMG) self-assembled monolayers (SAMs) on gold electrode were prepared and characterized by electrochemical measurements. The two sensors exhibit sensitive and selective response to Cu(II), both forming 2:1 complexes, the first one in acetic buffer and the second one in ammonia buffer. Copper determination at trace level (LOQ 0.2 and 0.3 μg/L for d , l -penicillamine and TDMG, respectively) is possible with both the electrodes as verified in tap, spring and sea water. The influence on copper determination of most common ions present in natural waters and of organic matter has been investigated. Accuracy was checked by recovery test on spiked samples.

The feasibility of ligand titrations with metal ions using complexing resins as sorbing solids is evaluated. The resins considered were the iminodiacetic resin Chelex 100, the carboxilic resin Amberlite CG50, and the anion exchange resin AG1X8, whose sorbing properties for aluminium(III) and copper(II) were known from previous investigations. Synthetical solutions containing known concentrations of ligands, EDTA and IDA were titrated separately with aluminium(III) and copper(II), by adding known concentration of titrant metal, and measuring the concentration of metal ion sorbed on the resin, c. The concentration of free metal ion was evaluated from c by the relationship: [M] = cV/K*w. K* is the ratio of the concentration of metal ion sorbed on the resin to the free metal ion in solution, and strongly depends on the conditions. In the case of the resins used in this investigation it can be calculated since the sorption equilibria of the metal ions are known. The total concentration of the ligands and the conditional stability constants are evaluated by a linearization procedure, previously proposed and widely used for ligand titrations, based on the hypothesis that only a 1 to 1 metal to ligand complex is formed. Accurate results are always obtained if the titration is properly carried out, i.e. using the appropriate resin, and adding the required excess of titrant. Some criteria are suggested to evaluate the results obtained, which can be useful when solutions of unknown composition are titrated. For these evaluations the sorption equilibria of metal ions on the resin at the considered conditions must be exactly known. In this paper they were evaluated from the sorbing properties of the resins, previously investigated according to the Gibbs–Donnan model. This is very convenient, since it avoids the experimental determination at each particular set of conditions, which is often even impossible, yet giving acceptable results.

The preparation and application of a humic acids modified gold electrode (HA-CME) have been described. Derivatization of HAs as β-thioesters caused their partial fragmentation and, thus, a consequent separation by size exclusion chromatography (SEC) was necessary. The CME prepared with functionalized HAs having an average MW of 52000 demonstrated to be effective for trace As(III) determination (LOQ = 0.3 μg L −1 ). This CME has been characterized both by electrochemical techniques and atomic force microscopy (AFM). The HA-CME provided reliable measurements in natural waters at different salinity with no need of desalting the sample. Total inorganic arsenic could be determined after reduction of As(V) with SO 2 . Under these conditions, organic arsenic species were not mineralized and did not interfere.

Cyclic voltammetric scans for methylarsonic acid, dimethylarsinic acid and 3-acetamido-4-hydroxyphenylarsonic acid at a mercury electrode in an acidic medium show anodic adsorption waves when the starting potential is sufficiently negative; the related arsines are formed on the electrode. Detection limits are at the micromolar level for the absorption peak found at about −0.1 V vs. SCE for all three compounds. Interferences are discussed.