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An efficient assisted transport of Fe(III) ions using a bulk liquid membrane containing 2-hydroxybenzaldeyde benzoylhydrazone in toluene has been applied as a separation and preconcentration process for the analysis and speciation of dissolved iron traces in natural and sea waters. A study strategy based on a modified simplex design has been followed to optimise the transport of Fe(III) ions through the liquid membrane. Maximum carrier-mediated transport efficiencies were obtained at following conditions: pH 1.9 for feed aqueous solution; 0.014 mol L− 1 of ligand in toluene as carrier and 2.9 mol L− 1 HNO3 in the stripping solution. Under optimal conditions, the average recovery of Fe(III) ions was 102 ± 2% (n = 7) for 6 h at 35 °C and the preconcentration factor of the method was 18.1. The influence of saline matrix was negligible and experiments at slightly high temperatures led to reduced preconcentration times. The accuracy of the method was verified by using the TMDA-62 certified reference water sample and successfully applied to the analysis of Fe(III) in river and seawater samples from Tangier (Morocco). Due to the proposed liquid membrane system allowed the selective separation and preconcentration of Fe(III) ions but not Fe(II) ions, a scheme for speciation analysis of dissolved iron was proposed. The distribution of total dissolved Fe, non-labile Fe, labile Fe(II) and labile Fe(III) fractions was performed in real seawater samples with successful results in good agreement with those obtained by adsorptive cathodic stripping voltammetry (average relative error of ± 3%).

A disposable and miniaturised optical sensor based on colorimetric solid-phase extraction has been designed using poly(styrene-divinylbenzene) membrane disks modified with the colorimetric reagent pyridoxal salicyloylhydrazone to determine the aluminium concentration in aqueous solutions. The extraction of Al(III) ions by the reagent immobilised onto a disk allows the quantification directly on the adsorbent surface by a miniature portable reflectance spectrometer with an optical fibre at 434 nm. The optimisation of the sensing system was carried out by a fractional factorial design 33−1 considering the extraction pH, amount of ligand immobilised onto the disk and time of immobilisation as experimental factors. The linear dynamic range of the sensor response ranged from 0.18 to 2 mg L−1 Al(III) with a detection limit of 0.18 mg L−1 (n = 10), being the precision of 6.3% for 1 mg L−1 Al(III) (n = 10, confidence level of 95%). The proposed method was successfully applied to the analysis of aluminium in leachates from cookware, antacids and hygienic care products, as contribution to the concern about aluminium as a known systemic toxicant at high doses.

A novel polymer inclusion membrane (PIM), doped with pyridine-2-acetaldehyde benzoylhydrazone (2-APBH) as extractant, was synthesized and applied for the simultaneous extraction and preconcentration of Cu(II), Ni(II) and Cd(II) ions from natural waters of different salinities. Poly(vinyl chloride) (PVC) and tributyl phosphate (TBP) were used to prepare the polymeric membrane. The carrier-mediated extraction of Cu(II), Ni(II) and Cd(II) ions by PIM was based on the reaction of 2-APBH as a polydentate ligand, forming uncharged chelates at pH 8. After a back-extraction step from the membrane to an acid solution (0.3 mol L-1 nitric acid), these ions were quantitative determined by flame atomic absorption spectroscopy. The optimum values of different analytical variables were determined by using the modified simplex method. The results showed limits of detection of 0.33 µg L-1 for Cu(II), 0.75 µg L-1 for Ni(II) and 0.48 µg L-1 for Cd(II). The accuracy was successfully assessed by analyzing a certified reference river water (LGC 6019). The applicability of the proposed PIM on real samples was also demonstrated on estuarine and seawater samples, with high salinities.

A single-use optical sensor was designed for Zn(II) determination based on the immobilisation of the colorimetric reagent 2-acetylpyridine benzoylhydrazone (2-APBH) in a polymer inclusion membrane (PIM) adhered on the surface of an inert rectangular strip of polyester (Mylar). Different components for the membrane preparation were tested and those resulting in membrane with good appearance, proper physical and optical properties and ease of preparation were selected. Factorial design 23 with three replicates of the central point was applied for the optimisation of the membrane composition. The optimal composition consisted of 2.5 g of poly(vinyl chloride) (PVC), 4 mL of tributyl phosphate (TBP) and 0.04 g of 2-APBH. The optode showed a linear dynamic range from 0.03 (detection limit) to 1 mg L−1 of Zn(II) ions with a response time of 30 min in aqueous solution at pH 6 and a relative standard deviation of 3.90% for 0.4 mg L−1 of Zn(II). The sensor exhibited good selectivity to Zn(II) over other commonly ions. It was successfully applied to the determination of Zn(II) in a water certified reference material, spiked tap water, vitamin-mineral drink, food supplement and foot health care products, as contribution to the concern about this heavy metal due to its significant role in many biological and physiological processes although toxicant at high doses.

A tandem system based on the coupling of a bulk liquid membrane and a flow injection analysis for the separation, preconcentration and spectrophotometric determination of copper in saline water is presented. The ligand pyridine-2-acetaldehyde benzoylhydrazone has been used as a carrier in the liquid membrane as well as a spectrophotometric reagent for UV–VIS detection. Simultaneous and sequential experimental designs were used to optimise the chosen variables of each technique, respectively. The metal was separated and preconcentrated from the sample with an efficiency of 100.5 ± 0.9% and a metal preconcentration factor of 16.1. The on-line FIA determination was accomplished after metal complexation by the reagent at pH 3. A linear response was obtained in a range from 6.9 to 984.5 µg L–1 Cu(II), providing a detection limit of 1.8 µg L–1. Saline matrix and other metal ions were not cause of interferences with relative errors below 4.6% for 50 µg L−1 of Cu(II) determination. The proposed tandem system was successfully tested using a TMDA-62 certified reference material providing a relative error of + 1.9%; it was also applied to the Cu(II) determination in coastal seawater samples with low relative errors ranging from − 3.8% to 0.0% (using DPASV as reference method).