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In this work, titanium phosphate nanoparticles were modified with different electroactive metals (cadmium, bismuth, copper, silver and mercury), by a cation-exchange reaction. The amount of metal introduced into the nanoparticles depended strongly on the counter-ion used during the exchange reaction and the type of metal. Nanoparticles with a high metallic load could be generated. The electrolytic medium played an important role in the detection of these metal-modified nanoparticles, since the use of acid makes it possible to extract a large part of the introduced metal by reversing the cation-exchange reaction. The application of these nanoparticles in electrochemical detection was evaluated, the nanoparticles modified with copper and mercury proving superior in terms of sensitivity and selectivity in multiplex detection. As a proof of concept, these nanoparticles were used as labels in a multiplex electrochemical biosensor for the simultaneous detection of two analytes. ; This work has been supported by the FC-15-GRUPIN-021 project from the Asturias Regional Government and the CTQ2014-58826-R project from the Spanish Ministry of Economy and Competitiveness (MEC). ; Peer Reviewed

In this work, we report a simple and yet efficient stencil-printed electrochemical platform that can be integrated into the caps of sample containers and thus, allows in-field quantification of Cd(II) and Pb(II) in river water samples. The device exploits the low-cost features of carbon (as electrode material) and paper/polyester transparency sheets (as substrate). Electrochemical analysis of the working electrodes prepared on different substrates (polyester transparency sheets, chromatographic, tracing and office papers) with hexaammineruthenium(III) showed that their electroactive area and electron transfer kinetics are highly affected by the porosity of the material. Electrodes prepared on transparency substrates showed the best electroanalytical performance for the simultaneous determination of Cd(II) and Pb(II) by square-wave anodic stripping voltammetry. Interestingly, the temperature and time at which the carbon ink was cured had significant effect on the electrochemical response, especially the capacitive current. The amount of Cd and Pb on the electrode surface can be increased about 20% by in situ electrodeposition of bismuth. The electrochemical platform showed a linear range comprised between 1 and 200 mg/L for both metals, sensitivity of analysis of 0.22 and 0.087 mA/ppb and limits of detection of 0.2 and 0.3 mg/L for Cd(II) and Pb(II), respectively. The analysis of river water samples was done directly in the container where the sample was collected, which simplifies the procedure and approaches field analysis. The developed point-of-need detection system allowed simultaneous determination of Cd(II) and Pb(II) in those samples using the standard addition method with precise and accurate results ; This work has been supported by the FC-15-GRUPIN-021 project from the Asturias Regional Government and the CTQ2014-58826-R project from the Spanish Ministry of Economy and Competitiveness (MINECO). Daniel Martín-Yerga thanks the MINECO for the award of a FPI grant (BES-2012-054408). Isabel Alvarez-Martos ...

A novel approach is presented, whereby gold nanostructured screen-printed carbon electrodes (SPCnAuEs) are combined with in-situ ionic liquid formation dispersive liquid–liquid microextraction (in-situ IL-DLLME) and microvolume back-extraction for the determination of mercury in water samples. In-situ IL-DLLME is based on a simple metathesis reaction between a water-miscible IL and a salt to form a water-immiscible IL into sample solution. Mercury complex with ammonium pyrrolidinedithiocarbamate is extracted from sample solution into the water-immiscible IL formed in-situ. Then, an ultrasound-assisted procedure is employed to back-extract the mercury into 10 µL of a 4 M HCl aqueous solution, which is finally analyzed using SPCnAuEs. Sample preparation methodology was optimized using a multivariate optimization strategy. Under optimized conditions, a linear range between 0.5 and 10 µg L−1 was obtained with a correlation coefficient of 0.997 for six calibration points. The limit of detection obtained was 0.2 µg L−1, which is lower than the threshold value established by the Environmental Protection Agency and European Union (i.e., 2 µg L−1 and 1 µg L−1, respectively). The repeatability of the proposed method was evaluated at two different spiking levels (3 and 10 µg L−1) and a coefficient of variation of 13% was obtained in both cases. The performance of the proposed methodology was evaluated in real-world water samples including tap water, bottled water, river water and industrial wastewater. Relative recoveries between 95% and 108% were obtained. ; The authors would like to thank the Spanish Ministry of Science and Innovation (Project nos. CTQ2011-23968 and CTQ2011-24560), the Generalitat Valenciana (Spain) (Project nos. ACOMP/2013/072, PROMETEO/2013/038 and GV/2014/096) and the University of Alicante (Spain) (Project no. GRE12-45) for the financial support. E. Fernández and D. Martín-Yerga also thank Generalitat Valenciana and Ministry of Economy and Competitiveness, respectively, for their fellowships.