Hadi Khani

Multi-walled carbon nanotubes-ionic liquid-carbon paste electrode as a super selectivity sensor: Application to potentiometric monitoring of mercury ion(II)

In this article a super selectivity potentiometric methodology, using an ion-selective electrode, for determination of mercury ion(II) in aqueous solution was investigated. For modification of the electrode a room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF(4)), was applied as a super conductive binder, and Multi-walled carbon nanotubes (MWCNTs) was used in the composition of the carbon paste to improve conductivity and transduction of chemical signal to electrical signal. Moreover, incorporation of 1-(2-ethoxyphenyl)-3-(3-nitrophenyl)triazene (ENTZ) as an ionophore to this composition caused to significantly enhanced selectivity toward Hg(II) ions over a wide concentration range of 1.0×10(-4) to 5.0×10(-9) M with a lower detection limit of 2.5×10(-9) M (0.5 ppb) and a Nernstian slope of 29.3±(0.2) mV decade(-1) of Hg(II) activity. The electrode has a short response time (∼5s) and can be used for at least 55 days without any considerable divergence in potentials, and the working pH range was 2.0-4.3. Finally, the proposed electrode was successfully used as an indicator for potentiometric determination of Hg(II) in dental amalgam and water samples.

Adsorption process of methyl orange dye onto mesoporous carbon material-kinetic and thermodynamic studies.

The mesoporous carbon CMK-3 adsorbent was prepared, characterized, and used for the removal of anionic methyl orange dye from aqueous solution. Adsorption experiments were carried out as batch studies at different contact time, pH, initial dye concentration, and salt concentration. The dye adsorption equilibrium was rapidly attained after 60 min of contact time. Removal of dye in acidic solutions was better than in basic solutions. The adsorption of dye increased with increasing initial dye concentration and salt concentration. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the methyl orange adsorption than Freundlich model. Experimental data were analyzed using pseudo-first-order and pseudo-second-order kinetic models. It was found that kinetics followed a pseudo-second-order equation. Thermodynamic study showed that the adsorption was a spontaneous and exothermic process.

Prediction of capillary gas chromatographic retention times of fatty acid methyl esters in human blood using MLR, PLS and back-propagation artificial neural networks

Quantitative structure-retention relationship (QSRR) models correlating the retention times of fatty acid methyl esters in high resolution capillary gas chromatography and their structures were developed based on non-linear and linear modeling methods. Genetic algorithm (GA) was used for the selection of the variables that resulted in the best-fitted models. Gravitational index (G2), number of cis double bond (NcDB) and number of trans double bond (NtDB) were selected among a large number of descriptors. The selected descriptors were considered as inputs for artificial neural networks (ANNs) with three different weights update functions including Levenberg-Marquardt backpropagation network (LM-ANN), BFGS (Broyden, Fletcher, Goldfarb, and Shanno) quasi-Newton backpropagation (BFG-ANN) and conjugate gradient backpropagation with Polak-Ribiére updates (CGP-ANN). Computational result indicates that the LM-ANN method has better predictive power than the other methods. The model was also tested successfully for external validation criteria. Standard error for the training set using LM-ANN was SE=0.932 with correlation coefficient R=0.996. For the prediction and validation sets, standard error was SE=0.645 and SE=0.445 and correlation coefficient was R=0.999 and R=0.999, respectively. The accuracy of 3-2-1 LM-ANN model was illustrated using leave multiple out-cross validations (LMO-CVs) and Y-randomization.

Sol-Gel-Au nano-particle modified carbon paste electrode for potentiometric determination of sub ppb level of Al(III)

This work describes a new carbon paste electrode modified by Sol-Gel-Au nano-particle (SGAN) in the presence of 2,2′-dihydroxy-1-naphthylidine-1′-naphthyl methyl amine (DNMA) as ionophore for determination of Al(III) by potentiometric method. Gold nano-particles (GNPs) were self-assembled onto silica Sol-Gel network and incorporated within carbon paste. The nano-structured matrix with DNMA shows well-defined potentiometric behavior for the determination of Al3+ in aqueous solutions. The sensor exhibits significantly enhanced selectivity toward Al3+ ions over a wide concentration range of 5.0 × 10−10 to 5.0 × 10−2 M with a lower detection limit of 2.0 × 10−10 M (0.054 ppb) and a Nernstian slope of 20.0 ± (0.1) mV decade−1 of Al3+ activity. It has a fast response time of 5 s and can be used for at least 70 days without any considerable divergence in potentials. The potentiometric response of the electrode is independent of pH of test solution in the pH range 3–7. The interaction between DNMA and Al3+ was studied spectrophotometrically and it exhibits that stoichiometry of complex is 1 : 1 in methanol solution. Finally, this electrode was successfully used as an indicator electrode for potentiometric determination of Al3+ in some real samples.

Comparative studies of mercapto thiadiazoles self-assembled on gold nanoparticle as ionophores for Cu(II) carbon paste sensors.

Comparative studies of the potentiometric behavior of three mercapto compounds [2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol] (MTMP), [5-(2-methoxy benzylidene amino)-1,3,4-thiadiazole-2-thiol] (MBYT) and [5-(pyridin-2-ylmethyleneamino)-1,3,4-thiadiazole-2-thiol] (PYTT) self-assembled on gold nanoparticles (GNPs) as ionophores in carbon paste electrodes (CPEs) have been made. These mercapto thiadiazole compounds were self-assembled onto gold nanoparticles and then incorporated within carbon paste electrode. The self-assembled ionophores exhibit a high selectivity for copper ion (Cu(2+)), in which the sulfur and nitrogen atoms in their structure play a role as the effective coordination donor site for the copper ion. These carbon paste electrodes were applied as indicator electrodes for potentiometric determination of copper ions. The sensor based on PYTT exhibits the working concentration range of 4.0 x 10(-9) to 7.0 x 10(-2) M and a Nernstian slope of 28.7+/-0.3 mV decade(-1) of copper activity. The detection limit of electrode was 1.0 x 10(-9) M and potential response was pH independent across the range of 3.0-6.5. It exhibited a quick response time of <5 s and could be used for a period of 45 days. The ion selectivity of this electrode for Cu(2+) was over 10(4) times that for other metal cations. The application of prepared sensors has been demonstrated for the determination of copper ions in spiked water and natural water samples.

Selective extraction and preconcentration of ultra-trace level of mercury ions in water and fish samples using Fe3O4-magnetite-nanoparticles functionalized by triazene compound prior to its determination by inductively coupled plasma-optical emission spectrometry

In this paper, new modified magnetite nanoparticles functionalized with triazene groups were designed and synthesized for extraction/preconcentration of sub-ppb level of mercury ions in water and fish samples prior to its determination with inductively coupled plasma optical emission spectrometry (ICP-OES). In the separation process, aqueous solution of Hg2+ ions was mixed with 150 mg of Fe3O4 magnetite nanoparticles modified with 1-(p-acetyl phenyl)-3-(o-ethoxy phenyl) triazene (AET) and then external magnetic field was applied for isolation of magnetite nanoparticles containing mercury ions. Experimental conditions for effective adsorption including pH, sample volume, eluent concentration and existing co-existing ions have been studied and established. Under the optimal extraction and preconcentration conditions, the limit of detection (LOD) of 0.04 ng mL−1 and the relative standard deviation (R.S.D) of 2.09% for five replicate extractions and measurements of 10 μg of Hg2+ ion in 1000 mL water solution were achieved by ICP-OES. The sorption capacity of functionalized Fe3O4 magnetite nanoparticles under optimum conditions has been found to be 10.26 mg of mercury ion per gram at pH 7 with the preconcentration factor of 500 (2 mL of elution for a 1000 mL sample volume). Standard solutions containing Hg2+ in the concentration range of 0.2–200 ng mL−1 were examined by the proposed procedure and it was observed that calibration curve was linear in this range (R2 = 0.999). The special advantages of the proposed method are high enrichment factor, fast separation and low detection limits compared with other methods.

A novel extraction and preconcentration of ultra-trace levels of uranium ions in natural water samples using functionalized magnetic-nanoparticles prior to their determination by inductively coupled plasma-optical emission spectrometry

New modified magnetic nanoparticles functionalized with salicylaldehyde groups were designed and synthesized to produce a Schiff base-sorbent for extraction/preconcentration of sub-ppb levels of uranium ions in water samples prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). In the separation process, an aqueous solution of U(VI) ions was mixed with 100 mg of functionalized Fe3O4 magnetic nanoparticles with salicylaldehyde groups (Sal-APS-FMNPs) and then an external magnetic field was applied for isolation of Sal-APS-FMNPs containing uranium ions. Experimental conditions for an effective adsorption including pH, sample volume, eluent concentration, and presence of co-existing ions have been studied and established. Under the optimal extraction and preconcentration conditions, a limit of detection (LOD) of 0.24 ng mL−1 and a relative standard deviation (RSD) of 1.5% (n = 8) were achieved by ICP-OES. The analytical curve was linear in the range 1–5000 ng mL−1. Under the optimum conditions, the sorption capacity of Sal-APS-FMNPs has been found to be 49 mg of U(VI) ions per gram at pH 7 with a preconcentration factor of 1000 (1 mL of elution for a 1000 mL sample volume). The proposed method is characterized with high enrichment factor, easy preparation and regeneration of sorbent, short time of sample pretreatment, fast and really clean separation, high extraction yields, wide linear curve, and low detection limits. Finally, the proposed method was successfully used for extraction, preconcentration, and determination of U(VI) ions in some real samples.

Highly selective determination of trace quantities of Hg(II) in water samples by spectrophotometric and inductively coupled plasma-optical emission spectrometry methods after cloud point extraction

A cloud-point extraction method for preconcentration of ultra-trace quantities of mercury ions as a prior step to its determination by spectrophotometry is presented and discussed. Cloud-point extraction was carried out using [1-(2-ethoxy phenyl)-3-(2-chloro phenyl)] triazene (EOCT) as the chelating agent and Triton X-114 as the non-ionic surfactant. The preconcentrated mercury was then determined spectrophotometrically by measuring the absorbance of the surfactant rich phase at 366 nm and also by measuring the emission intensities in the ICP-OES signals at 253.7 nm. Linearity was obeyed in the range of 8.0–150.0 ng mL−1 and 20–200 ng mL−1 by ICP-OES and spectrophotometry, respectively. The variable affecting the combined preconcentration-emission and absorption methods have been evaluated and optimized. Under the optimum condition, the detection limit of 1.03 ng mL−1 and 5.46 ng mL−1 were achieved using ICP-OES and UV-vis, respectively. The results in this paper will show using spectrophotometric method after cloud-point extraction can be an appropriate method for determining of mercury concentration at the ppb level in place of ICP-OES which is too costly a method. The interference effect of some anions and cations was also tested. Finally, the proposed method was successfully used for determination of Hg(II) in some real samples.