A novel microextraction technique based on 1-hexylpyridinium hexafluorophosphate ionic liquid for the preconcentration of zinc in water and milk samples.

Simultaneous preconcentration of Cd(II), Cu(II) and Pb(II) on Nano-TiO2 modified with 2-mercaptobenzothiazole prior to flame atomic absorption spectrometric determination

Photoexcited quantum dots (QDs) offer a wealth of mechanisms for interactions with the valence band holes or conduction band electrons, influencing electron–hole recombination. The potential to use combinations of these mechanistic pathways to achieve detection of different metal ions with one modified QD system has been tested. Dual-function water-soluble core/shell-modified CdSe/ZnS quantum dot nanoparticles have been created, that exploit two different fluorescence emission pathways for the detection of two heavy metal ions: Zn2+ and Mn2+. A QD-zincon system is proposed, which shows a static Perrin-type quenching mechanism, with sphere of action radii 1.1, 1.3 and 1.6 nm respectively, for 500, 540 and 620 nm QD emission. The QD-zincon system was produced using a layer-by-layer approach: mercaptopropionic acid-capped QDs were modified with a positive polyelectrolyte by electrostatic interaction and then a negatively charged chromogenic reagent, zincon, classically used for the determination of metals. QD-zincon is able to coordinate both Zn2+ and Mn2+ and, by exploiting two different mechanisms, QD-zincon conjugates can be tailored to respond to Zn2+ or Mn2+. Upon coordination of zincon with Mn2+, a dramatic enhancement of the fluorescence intensity results as the quenching interaction between zincon and QDs is deactivated, thereby ‘switching on the fluorescence emission’. The versatility of this system is demonstrated in terms of fluorescent emission wavelength, which could be selected across a wide range, through choice of QDs (examples are shown for λmax = 500, 540 and 620 nm). In contrast, in the case of Zn2+ detection, the mechanism is based on the radiationless resonance energy transfer (RET) from QDs acting as donor, to the acceptor zincon-Zn2+, since its absorption spectra offer adequate overlap with the emission spectra of QD540 and QD620, producing a useful analytical signal by the RET process. Using these different operating principles, CdSe/ZnS core/shell QD-zincon conjugates showed very good linearity in the range 10–1000 µM and 5–500 µM for Zn2+ and Mn2+ nanosensors, respectively, and RSDs about 3% (n = 10). In a study of interferences, the QD–zincon conjugate showed higher selectivity than the corresponding method with zincon in solution. The results from synthetic ionic mixtures suggested very good applicability in the determination of Zn2+ and Mn2+ in samples containing other metal ions, with just a small reduction of sensitivity at very high ionic concentration.

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Multiplexed energy transfer mechanisms in a dual-function quantum dot for zinc and manganese

Antimony, a pollutant of emerging concern: A review on industrial sources and remediation technologies

A new cloud point extraction procedure for determination of inorganic antimony species in beverages and biological samples by flame atomic absorption spectrometry

An optical sensor has been designed for the determination of zinc by spectrophotometry. The sensing membrane is made by immobilizing Zincon as an ion pair with methyltrioctylammonium ion on triacetylcellulose membrane. In the present of Zn2+ ions in ammonia/ammonium chloride buffer at pH 9 the color of the membrane changes from purple to blue. The calibration curve was linear in the range of 0.76–30.60 μM of Zn2+ ion with a limit of detection 0.16 μM (10.5 ng ml−1). The response time of the optode was about 10–12 min, depending on the concentration of Zn2+. The sensor can readily be regenerated with hydrochloric acid solution. This optode is stable and could be stored under water for three weeks without reagent leaching. The relative standard deviation for seven replicate measurements of 7.65 and 15.30 μM Zn2+ was 3.09 and 2.82%, respectively. The sensor was successfully applied to the determination of zinc in powdered milk and hair samples.

/pdf/an-optical-sensor-for-zinc-determination-based-on-zincon-as-50a1twej95.pdf

An optical sensor for zinc determination based on Zincon as sensing reagent

Sol-gel based optical sensor for determination of Fe (II): a novel probe for iron speciation.

We report on a simple, sensitive and reliable method for the cloud point extraction of antimony (Sb) and its subsequent spectrophotometric detection. It is based on the color reaction of Sb (III) with iodide in acidic medium and subsequent micelle-mediated extraction of tetraiodoantimonate using a non-ionic surfactant in the absence of any chelating agent. The effects of reaction and extraction parameters were optimized. The calibration plot is linear in the range of 0.80–95 ng mL−1 of antimony in the sample solution, with a regression coefficient (r) of 0.9994 (for n = 9). The detection limit (at SNR = 3) is 0.23 ng mL−1, and the relative standard deviations at 10 and 70 ng mL−1 of antimony are 3.32 and 1.85 % (at n = 8), respectively. The method compared favorably to other methods and was applied to determine antimony in seawater, anti-leishmania drug (glucantime), and human serum.

A cloud point extraction for spectrophotometric determination of ultra- trace antimony without chelating agent in environmental and biological samples

We report herein the development of a novel optical sensor based on incorporation of 1,5-diphenylcarbazone as a sensitive reagent into the nanopores of a transparent glass like material through the sol–gel process and suggest how it may be useful for determination of zinc in aqueous solutions. The sensors were fabricated by spin-coating onto glass substrates. To survey the catalysis type effect on leaching behavior of the sensor, both acid- and base-catalyzed sol–gel processes were studied. Results indicated that acid-catalyzed method is suitable to give more stable thin films with constant sensitivity and response time for a long period of time. The fabricated sensor can be used for determination of zinc in the range of 0.03–1.2 μg mL−1 with a detection limit of 0.016 μg mL−1. It also showed reproducible results with relative standard deviation of 3.6 and 2.2% for 0.1 and 0.8 μg mL−1 of Zn (II), respectively, along with a fast response time of ∼150 s. This optode is stable and could be stored for at least 2 months without observing any change in its sensitivity. The developed sensor was successfully applied to the determination of zinc in serum of diabetic patients and water sample and validated against inductively coupled plasma optical emission spectrometry method.

A new sol–gel optical sensor with nonporous structure for determination of trace zinc

An optical sensor has been proposed for the determination of silver by spectrophotometry. The sensor was prepared by immobilizing 5(p-dimethylaminobenzylidene)rhodanine on a transparent triacetylcellulose membrane. The effect of different variables on the response of the sensor was studied and the optimum conditions were established. The sensor responded linearly in the range 1.8–55.6 μM of silver with a limit of detection of 0.8 μM and a response time range of 8–10 min depending on the concentration of the silver ions. The presented optode is reversible and stable if stored in water for more than one month without reagent leaching. The relative standard deviation for seven replicated measurement of 4.6 and 37 μM silver was 3.15 and 2.76%, respectively. The sensor was successfully applied to the determination of silver in a silver sulphadiazine cream, an ore sample, and a radiology film.

Vida Rezaei

Papers

An optical sensor for zinc determination based on Zincon as sensing reagent

Sol-gel based optical sensor for determination of Fe (II): a novel probe for iron speciation.

A cloud point extraction for spectrophotometric determination of ultra- trace antimony without chelating agent in environmental and biological samples

A new sol–gel optical sensor with nonporous structure for determination of trace zinc

A silver optical sensor based on 5(p-dimethylaminobenzylidene)rhodanine immobilized on a triacetylcellulose membrane