This article reports the first fluorescent distance-based paper device coupled with an evaporating preconcentration system for determining trace mercury ions (Hg2+) in water.
A paper-based method for heating preconcentration (PAD-HP) has been developed for the determination of Pb 2+ , Cd 2+ , Fe 3+ , and Ni 2+ . The design of our heating system was evaluated for dual quantification of ions using electrochemical and colorimetric methods simultaneously. The PAD-HP was used to detect Pb 2+ and Cd 2+ by anodic stripping voltammetry and to detect Fe 3+ and Ni 2+ by colorimetric reactions. Assay conditions were optimized by evaluating performance when changing the concentration of the colorimetric reagent, eluent volume, electrolyte concentration, and electrochemical parameters. Limits of detection (LOD) were determined to be 0.97 and 2.33 μg L −1 for Pb 2+ and Cd 2+ (via voltammetry) and 0.03 and 0.04 mg L −1 for Fe 3+ and Ni 2+ (via colorimetric assay), respectively. The relative standard deviations for assays were in the range of 5.76 to 10.12%. We observed that the PAD-HP method significantly enhanced the signal of all metals ions (14−100-fold, depending on the metal) in comparison to paper-based devices that did not use a heating preconcentration system. This PAD-HP method was successfully applied to the determination of metals ions in samples of drinking water, tap water, pond water, and wastewater. These results suggest that our approach can provide a convenient strategy to monitor aqueous samples for heavy metals with high sensitivity and selectivity.
We report for the first time a distance-based paper device based on gold/silver core shell nanoparticles (Au@Ag NPs) for a simple, inexpensive, instrument-free, and portable determination of cyanide by the naked eye. Au@Ag NPs immobilized on a paper channel were etched by cyanide ions so that a yellow color band length of Au@Ag NPs is proportional to a decrease in the cyanide concentration. Quantification is achieved by measuring color length, thus eliminating the need to differentiate hues and intensities by the user, and the processing data of each imaging device. Moreover, the paper-based headspace extraction was combined with the distance-based paper device to improve the sensitivity. The enrichment factor was found to be 30-fold and the linearity was found in the range 0.05–1 mg L−1. The naked eye detection limit was 10 μg L−1 where the World Health Organization (WHO) have regulated the maximum level of cyanide in drinking water as 70 μg L−1. Our proposed device also showed no interference from common cations and anions presenting in seawater and waste water including thiocyanate, chloride. Finally, our device has been successfully applied to determine cyanide ions in seawater, drinking water, tap water and wastewater providing satisfactory precision and accuracy.
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