Constructing a new optical sensor for monitoring ammonia in water samples using bis(acetylacetoneethylendiamine)-tributylphosphin cobalt(III) tetraphenylborate complex-coated triacetylcellulose.

A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water.     

Effect of gold nanoparticle as a novel nanocatalyst on luminol-hydrazine chemiluminescence system and its analytical application

In this work the catalytic role of unsupported gold nanoparticles on the luminol–hydrazine reaction is investigated. Gold nanoparticles catalyze the reaction of hydrazine and dissolved oxygen to generate hydrogen peroxide and also catalyze the oxidation of luminol by the produced hydrogen peroxide. The result is an intense chemiluminescence (CL) due to the excited 3-aminophthalate anion. In the absence of gold nanoparticles no detectable CL was observed by the reaction of luminol and hydrazine unless an external oxidant is present in the system. The size effect of gold nanoparticles on the CL intensity was investigated. The most intensive CL signals were obtained with 15-nm gold nanoparticles. UV–vis spectra and transmission electron microscopy studies were used to investigate the CL mechanism. The luminol and hydroxide ion concentration, gold nanoparticles size and flow rate were optimized. The proposed method was successfully applied to the determination of hydrazine in boiler feed water samples. Between 0.1 and 30 μM of hydrazine could be determined with a detection limit of 30 nM.     

Application of 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo)phenol in construction of ion‐selective PVC membrane electrode for determination of copper (II) in mineral water sample

The potentiometric characteristics of a new Cu²⁺‐selective electrode based on 2‐(benzyliminomethyl)‐6‐methoxy‐4‐(4‐methoxyphenyl‐azo) phenol as an efficient ionophore has been evaluated. The effects of influential parameters on the potentiometric responses such as the amount of plasticizer, the amount of ionophore, pH of the sample solution, and the effect of coexisting ions on the electrode signal were subsequently investigated . The selectivity of the electrode was assessed by calculating the selectivity coefficients using the matched potential method. The optimum ratio of the amount of materials required for the preparation of the electrode was found to be 1.7: 32.1: 64.2: 2.0 corresponding to carboxylated PVC, dimethyl sebacate as solvent mediators, potassium tetrakis (p‐chlorophenyl) borate as the anion localizing agent, and ionophore, respectively. The electrode had a fast response (7s) as well as a satisfactory Nernstian slope (29.26±0.91 mV/decade) to Cu²⁺ over a wide concentration range of 2.0×10^?6‐ 5.0×10^?2 M with a low detection limit of 5.9×10^?7 M. The developed sensor was successfully used for the potentiometric titration of Cu²⁺ ion with EDTA and subsequently, efficient determination of this metal ion in a mineral water sample was performed.     

Study on the adsorption of DNA on Fe3O4 nanoparticles and on ionic liquid-modified Fe3O4 nanoparticles

We have investigated the adsorption of herring sperm DNA on Fe₃O₄ magnetic nanoparticles (NPs) before and after modification with the ionic liquid 1-hexyl-3-methylimidazolium bromide. Experiments were performed in a batch mode, and the effects of DNA concentration, pH of the sample solution, ionic strength, temperature, and contact time between reagents were optimized. An evaluation of the adsorption isotherm revealed that the Langmuir model better fits the equilibrium data than the Freundlich model. The maximum adsorption capacities of the unmodified and modified NPs, respectively, were found to be 11.8 and 19.8 mg DNA per gram of adsorbent. The adsorption of DNA onto the modified NPs was endothermic, while it was exothermic in the case of the unmodified NPs. The DNA can be desorbed from the modified surfaces of the NPs by using EDTA as the eluent. The NPs were able to adsorb about 90?±?1.5 % of DNA after being recycled for three times. The method is simple, fast, robust, and does not require organic solvents or sophisticated equipment.

Adsorption characteristics of Titan yellow and Congo red on CoFe2O4 magnetic nanoparticles

This paper assesses the adsorption characteristics of Titan yellow and Congo red on CoFe₂O₄ magnetic nanoparticles. The adsorption behavior of Titan yellow and Congo red from aqueous solution onto CoFe₂O₄ magnetic nanoparticles has been determined by investigating the effects of pH, concentration of the dye, amount of adsorbent, contact time, ionic strength and temperature. Experimental results indicated that CoFe₂O₄ nanoparticles can remove more than 98 % of each dye under optimum operational conditions of a dosage of 15.0 mg CoFe₂O₄, pH 3.0, initial dye concentration of 22–140 mg L^?1, and contact times of 2.0 and 15.0 min for Congo red and Titan yellow, respectively. Langmuir and Freundlich isotherm models have been used to evaluate the ongoing adsorption kinetic equations. Regeneration of the saturated adsorbent was possible by NaCl/acetone solution as eluent. The maximum adsorption capacities were 200.0 and 212.8 mg dye per gram adsorbent for Congo red and Titan yellow, respectively. With the help of adsorption isotherm, thermodynamic parameters such as free energy, enthalpy and entropy have been calculated. On the basis of pseudo-first-order and pseudo-second-order kinetic equations, different kinetic parameters have been obtained.     

Kinetic-catalytic determination of vanadium(IV) using methyl orange-bromate redox reaction.

Determination of V(IV) based on its catalytic effect on the reaction between Methyl Orange and bromate in thepresence of citric acid was studied. The calibration curve obtained by fixed-time method was linear in the range of 2.5-300 ng ml(-1). By use of slope method, a calibration curve containing two linear portions were obtained. Using fixed-time and slope methods, we obtained detection limits of 0.8 and 1.5 ng ml(-1), respectively. Fe2+, As(III), V(V) and Hg2+ interfered. The method was successful for analysis of water samples.     

Application of multivariate curve resolution analysis for studying the thermodynamics of methylene blue aggregations in aqueous solutions

In water, methylene blue (MB) is known to be aggregated to dimmer and trimmer at high concentration levels. We conducted a thermodynamic study on the aggregation of MB using multivariate curve resolution analysis of the visible absorbance spectra over a concentration range of 2.0 × 10^-6?4.0 × 10^-4 M. A hard modeling-based multivariate curve resolution method was applied to determine the dissociation constants of the MB aggregates at various temperatures ranging from 25 to 75 °C. This method was able to resolve the visible absorbance spectra as a function of MB concentration in individual temperature or simultaneously in all other temperature ranges. Utilizing the van??t Hoff relation, the enthalpy and entropy of the dissociation equilibriums were calculated. For the dissociation of both aggregates, the enthalpy and entropy changes were positive and negative, respectively.     

Micro-extraction and determination of transition metals in historical ink

A minimally invasive approach is described for sampling Fe, Cu, Zn and Mn in iron-gall ink. Filter paper (2?×?5 mm) that is moistened with de-ionized water is used to extract metals from an iron-gall ink surface. The extraction requires about 30–120 s for a small quantity of ink to diffuse into the moistened filter paper. The metals in the ink are extracted from the filter paper using 50 µL of concentrated nitric acid in a 2 mL polystyrene beaker for approximately 10 min. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify Fe, Cu, Zn and Mn in iron-gall ink. In order to test the feasibility of this extraction procedure, the ratio of Fe:Cu was determined from ink lines that were drawn with a commercially available iron-gall ink on modern acid-free paper. The measured ratio of Fe:Cu was 18.2:1 which is comparable to the expected ratio of 20:1. The slightly lower ratio achieved using the extraction procedure and GFAAS was possibly due to the higher solubility of the Cu species in the ink. One of the advantages of using a moistened filter paper is that only the ink surface is sampled which avoids the possible measurement of metals of different inks of other components that may be present in the paper or on the opposite side of the paper.     

Adsorption of acidic, basic, and neutral proteins from aqueous samples using Fe3O4 magnetic nanoparticles modified with an ionic liquid

We have prepared and characterized Fe₃O₄ nanoparticles and their binary mixtures (IL-Fe₃O₄) with 1-hexyl-3-methylimidazolium bromide as ionic liquid for use in the adsorption of lysozyme (LYS), bovine serum albumin (BSA), and myoglobin (MYO). The optimum operational conditions for the adsorption of proteins (at 0.05–2.0 mg?mL^?1) were 4.0 mg?mL^?1 of nanoparticles and a contact time of 10 min. The maximum adsorption capacities are 455, 182 and 143 mg for LYS, BSA, and MYO per gram of adsorbent, respectively. The Langmuir model better fits the adsorption isotherms, with adsorption constants of 0.003, 0.015 and 0.008 L?mg^?1, in order, for LYS, BSA, MYO. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated on the basis of comparative analysis of the corresponding rate parameters, equilibrium adsorption capacity and correlation coefficients. The adsorption processes are endothermic. The proteins can be desorbed from the nanoparticles by using NaCl solution at pH 9.5, and the nanoparticles thus can be recycled.