Dithizone nanofiber-coated membranes (dithizone membranes), which are useful for sensitive and selective determination of Hg(II), were fabricated. Simply by filtration of the aqueous dispersion of dithizone nanofiber through a cellulose ester membrane filter, a dithizone nanofiber layer of less than 500 nm thickness was coated firmly and uniformly over the membrane filter surface. The steel blue color of the membrane remained unchanged for more than three months when fabricated in the presence of ascorbic acid and stored with an oxygen absorber in an evacuated aluminium bag. Determination at the parts per billion level of Hg(II) was achieved by filtration-enrichment of a sample solution and simultaneous colorimetric analysis using a TLC scanner (500 nm). Consequently, Hg(II) ion was concentrated in the dithizone layer as reddish brown complexes by filtration of a sample solution at pH 2.7. More than 90% of 10 ppb Hg(II) was retained in the dithizone layer at the filtration rate of 1.3-9.3 ml min(-1). The presence of Na+ (10,000 ppm), K+ (5000 ppm), Ca(II) (5000 ppm), Cu(II) (6.4 ppm), Fe(II) (100 ppm), Zn(II) (100 ppm), Pb(II) (100 ppm) and Cd(II) (10 ppm) by using 2.5 x 10(-4) M of ethylenediamine tetraacetic acid (EDTA) as a masking reagent did not interfere with the detection of Hg(II) (10 ppb). Most of anions did not interfere with the determination of Hg(II). The present method was tested for the detection of simulated wastewater, river water and seawater spiked with 10 ppb of Hg(II).

Analytical test strips for heavy-metal ions can provide simple and convenient procedures for on-site analysis and daily monitoring of water quality without using costly instruments. However, since the standard limit values of heavy metals in the environment and drinking water are remarkably low (ppb level), the detection limits of commercial test strips (ppm level) are insufficient to satisfy the required criteria. In addition, since they are generally prepared by soaking paper in the signaling reagent, leakage of reagent is facile, and hence reliability and sensitivity of detection are poor. Firm fixation of colorimetric and fluorometric reagents for metals on solid substrates has been attempted by incorporation into PVCbased liquid membranes, [1] covalent anchoring with crosslinked copolymers, [2] and layer-by-layer accumulation methods such as Langmuir-Blodgett films [3,4] and alternate deposition of oppositely charged polyelectrolytes. [5,6] A wealth of information on optical sensors and probes for simple determination of heavy metals has been reviewed. [7] However, drawbacks include complicated synthetic procedures, insufficient sensitivity, requirements for auxiliary additives, and difficulty in controlling the concentration of the reagent and its uniformity. Hence, we sought a simple procedure for firm and uniform coating of signaling reagents on an appropriate substrate without any additional matrix.Recently, a simple and versatile process known as the "reprecipitation method" was proposed for the preparation of aqueous dispersions of organic nanoparticles.[8] The process involves injection of a water-miscible organic solution into water with vigorous stirring. We found that various organic nanoparticles can be uniformly coated onto a membrane filter (cellulose ester type) to form a thin layer simply by filtration of the nanoparticle dispersion. We attempted to apply this simple procedure to the fabrication of analytical test strips from a selection of signaling reagents. We examined popular indicator dyes having an aromatic conjugated system: dithizone (Dith), 1-(2-thiazolylazo)-2-naphthol (TAN), 1-(2-pyridylazo)-2-naphthol (PAN), tetraphenylporphin (TPP), and bathophenanthroline (Bathophen).Optimized preparative conditions for aqueous dispersions of the indicator dyes are listed in Table 1. Water-miscible acetone and THF were used for dissolution of the dyes. The pH of the aqueous phase was controlled to maintain electroneutrality of the dye species by considering the pK a values of the respective compounds. Smaller particles are formed with increasing temperature of the aqueous phase and with decreasing dye concentration in the organic phase.[9] Figure 1 shows scanning electron microscopy (SEM) images of TPP nanoparticles and PAN nanofibers. Round particles (50-100 nm) were mainly formed from TPP and Bathophen. In contrast, fibrous products were formed in the case of PAN, TAN, and Dith. These dyes commonly have dissociative protons capable of forming intermolecular hydrogen bonds which assist formation...

No abstract

Analytical test strips for heavy-metal ions can provide simple and convenient procedures for on-site analysis and daily monitoring of water quality without using costly instruments. However, since the standard limit values of heavy metals in the environment and drinking water are remarkably low (ppb level), the detection limits of commercial test strips (ppm level) are insufficient to satisfy the required criteria. In addition, since they are generally prepared by soaking paper in the signaling reagent, leakage of reagent is facile, and hence reliability and sensitivity of detection are poor. Firm fixation of colorimetric and fluorometric reagents for metals on solid substrates has been attempted by incorporation into PVCbased liquid membranes, [1] covalent anchoring with crosslinked copolymers, [2] and layer-by-layer accumulation methods such as Langmuir-Blodgett films [3,4] and alternate deposition of oppositely charged polyelectrolytes. [5,6] A wealth of information on optical sensors and probes for simple determination of heavy metals has been reviewed. [7] However, drawbacks include complicated synthetic procedures, insufficient sensitivity, requirements for auxiliary additives, and difficulty in controlling the concentration of the reagent and its uniformity. Hence, we sought a simple procedure for firm and uniform coating of signaling reagents on an appropriate substrate without any additional matrix.Recently, a simple and versatile process known as the "reprecipitation method" was proposed for the preparation of aqueous dispersions of organic nanoparticles.[8] The process involves injection of a water-miscible organic solution into water with vigorous stirring. We found that various organic nanoparticles can be uniformly coated onto a membrane filter (cellulose ester type) to form a thin layer simply by filtration of the nanoparticle dispersion. We attempted to apply this simple procedure to the fabrication of analytical test strips from a selection of signaling reagents. We examined popular indicator dyes having an aromatic conjugated system: dithizone (Dith), 1-(2-thiazolylazo)-2-naphthol (TAN), 1-(2-pyridylazo)-2-naphthol (PAN), tetraphenylporphin (TPP), and bathophenanthroline (Bathophen).Optimized preparative conditions for aqueous dispersions of the indicator dyes are listed in Table 1. Water-miscible acetone and THF were used for dissolution of the dyes. The pH of the aqueous phase was controlled to maintain electroneutrality of the dye species by considering the pK a values of the respective compounds. Smaller particles are formed with increasing temperature of the aqueous phase and with decreasing dye concentration in the organic phase.[9] Figure 1 shows scanning electron microscopy (SEM) images of TPP nanoparticles and PAN nanofibers. Round particles (50-100 nm) were mainly formed from TPP and Bathophen. In contrast, fibrous products were formed in the case of PAN, TAN, and Dith. These dyes commonly have dissociative protons capable of forming intermolecular hydrogen bonds which assist formation...

Anthracenes bearing aliphatic or aromatic amino substituents, which behave as molecular sensors, have shown their potential to act as photon-induced electron-transfer (PET) systems. In this PET, the fluorophore moieties are responsible for electron release during protonation and deprotonation. The principle of hard and soft acids and bases (HSAB) deals with both intra- and intermolecular electron migration. It is possible to calculate the localized properties in terms of Fukui functions in the realm of density functional theory (DFT) and thus calculate and establish a numerical matchmaking procedure that will generate an a priori rule for choosing the fluorophore in terms of its activity. We calculated the localized properties for neutral, anionic, and cationic systems to trace the course of the efficiency. A qualitative scale is proposed in terms of the feasibility of intramolecular hydrogen bonding. To investigate the effect of the environment of the nitrogen atom on protonation going from mono- to diprotonated systems, we calculated the partial density of states and compared the activity sequence with reactivity indices. The results show that location of the nitrogen atom in an aromatic ring does not influence the PET, but for aliphatic chains it plays a role. Furthermore, the protonation/deprotonation scenario has been explained. The results show that the reactivity indices can be used as a suitable property for scaling the activity of fluorophore molecules for the PET process.