Department of Chemistry
Shahid Beheshti University
Shahid Beheshti University
In this study, a new method based on homogeneous liquid–phase microextraction was developed for the determination of methamphetamine (MA) in urine samples. Dipropylamine (DPA), as a solvent with switchable hydrophilicity, was used as the extraction solvent and can be miscible/immiscible based on variable pH values of the aqueous sample solution. The effects of operational extraction parameters such as DPA volume, temperature, the amount of added acid and base solutions, and NaCl content of the sample were investigated. Under optimal conditions the preconcentration factor, limit of detection and linearity of the method were achieved in the ranges of 98.8, 1.5 μgL−1 and 5–1500 μgL−1, respectively. Also, within-run precision, between-run precision and robustness of the method were investigated. Finally, the proposed method was successfully applied to the analysis of MA in urine sample.
In this paper, the application of palladium nanoparticles supported on hyperbranched poly (ethylene glycol)- block-poly(citric acid)-functionalized Fe3O4 magnetic nanoparticles (Pd@PCA-b-PEG-Fe3O4) were evaluated as a new electrocatalyst in electrochemical sensing. The Pd@PCA-b-PEG-Fe3O4 was immobilized on the surface of a glassy carbon electrode (GCE) for the electrochemical reduction of hydrogen peroxide (H2O2). This electrode material was characterized by scanning electron microscopy (SEM), the transmission electron microscopy (TEM), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The Pd@PCA-b-PEG-Fe3O4 showed good electrocatalytic activity toward the reduction of H2O2 in the neutral phosphate buffer solution (pH 7.0). Moreover, the potential utility of the sensor was demonstrated by applying it to the analytical determination of H2O2 concentration. The results showed that the electrocatalytic current increased linearly with the H2O2 concentration in the range of 0.1–50.0 μM and the detection limit was 0.03 μM. Finally, the sensor has been successfully applied to determine H2O2 in water and urine samples with good accuracy and precision.
In this work, a new method based on homogeneous liquid-phase microextraction was developed for the determination of methadone and tramadol. Dipropylamine was used as extraction solvent with switchable hydrophilicity that can be miscible/ immiscible upon the addition or removal of CO2 as a reagent. The effects of operational parameters of the extraction such as volume of acceptor phase, volume of donor phase, pH of donor phase, and ionic strength of solution were investigated. Under optimal conditions, the preconcentration factors, the detection limits and the linearity of the method were achieved in the ranges of 135–138, 1.2 and 4–1000 μg L−1, respectively. Finally, the proposed method has been successfully applied to the analysis of methadone and tramadol in urine samples. In urine sample, the preconcentration factors were 118 and 122 for methadone and tramadol, respectively. Additionally, calibration curves were found to be linear in the concentration range of 8–1000 μg L−1 with the r2 values better than 0.998. In addition, limits of detection and quantification were 2.4 and 8 μg L−1, respectively, for both analytes.
In this article, a simple and efficient kind of homogeneous liquid-liquid microextraction based on an acid–base reaction using switchable-hydrophilicity solvents was proposed for the quantification of nitrazepam. Analyte is extracted into the N,N‑dipropylamine as an extraction solvent with the assistance of HCl and NaOH as pH adjustment reagents. Initially, a switchable solvent is added to the aqueous sample spiked with the analyte, which leads to the formation of a two phase mixture. Then, HCl is added drop by drop, until a clear and monophasic solution is obtained because of the switching of N,N‑dipropylamine into the hydrophilic form. Afterward, the separation of phases is achieved by addition of NaOH which results in switching back N,N‑dipropylamine to its primary hydrophobic form. Finally, after the evaporation of solvent, the extracted nitrazepam was analyzed by voltammetric methods. The influences of experimental factors on the extraction efficiency (organic solvent volume, pH of sample solution, extraction time, and salt addition) were investigated and optimized. Two linear ranges of 0.03–20 ng mL−1 and 20–450 ng mL−1 with the correlation coefficients of 0.996 and 0.998 were obtained from voltammetry measurements. The Limits of detection and quantification were obtained 9 ng L−1 and 0.03 ng mL−1 respectively. Also, the RSD% value of the method was calculated to be 7.4%. Finally, the proposed method was successfully applied for the determination of nitrazepam in human urine samples.
Benzofuran derivatives have many useful applications. Computational quantum chemistry method was used to study the relationship between energy data and molecular properties of the 5,6-dihydroxy-2-methyl-1- benzofuran-3-carboxylate derivatives (molecules 3a– 3f). Results indicate that there is a good relationship between intramolecular hydrogen bond lengths and energy data of these molecules. Also, X-ray of molecule 3e was used to compare experimental and computational geometrical parameters. Chemical hardness, chemical potential and electronegativity values were calculated to recognize relation between energy data and reactivity of these molecules. Atomic net charges and molecular electrostatic potential values were employed for better insight regarding energy data of the molecules. Electronic charge densities were calculated using atoms in molecules method. The correlation coefficients between experimental and computational 13C NMR chemical shifts were examined. Total spin– spin coupling constant and its components were evaluated to understand the contribution of these properties in energy data of the molecules. The relation between energy data of the molecules and aromaticity of the rings was also determined.
A novel approach is presented to determine 4- nitrobenzaldehyde in water samples. The procedure is based on switchable solvent based liquid-liquid microextraction (SS-LLME) and then determination by differential pulse voltammetry at multi-walled carbon nanotubes modified glassy carbon electrode. Dipropylamine, a solvent with switchable polarity, was used as an extraction solvent that can be miscible/immiscible upon the changes of pH of sample solution. Effects of experimental conditions on SS-LLME were investigated using a onefactor- at-a-time methodology. Under optimized conditions, a calibration curve was linear in the concentration range of 1.0 and 350 mgL1. Limits of quantification and detection were empirically 1.0 mgL1 and 0.3 mgL1, respectively. Intraday and Interday RSDs%, calculated in three concentration levels, were in the range of 6.2–7.8% confirm the proper precision of the method. Finally, the performance of the method was evaluated successfully in real samples including drinking water, tap water and river water
Pd/Al layered double hydroxide/carboxymethyl cellulose nanocomposite (CMC@Pd/Al-LDH) was fabricated using carboxymethyl cellulose as a green substrate via co-precipitation method. The synthesized nanocomposite was characterized using different methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, transmission electron microscopy, and electrochemical techniques. A glassy carbon electrode (GCE) was then modified with the suspended composite to obtain an electrochemical sensor for hydrogen peroxide (H2O2). The voltammetric (cathodic) current of the modified GCE was measured at −380 mV (vs. Ag/ AgCl), at the scan rate of 50 mV.s−1. Results show a linear dynamic range of 1 to 120 μM, and a 0.3 μM limit of detection (at S/N = 3). Intraday and interday relative standard deviations are in the ranges of 4.9–5.4% and 6.8– 7.3%, respectively. The sensor was applied for the determination of H2O2 in basil extracts, milk, and spiked river water samples. The recoveries are between 96.60 and 102.30%.
Fused pyrimidine derivatives have participated in the structure of various medicinally significant compounds especially as the privileged motifs for anticancer agent’s design purposes . Among fused pyrimidine derivatives, pyrido [2,3-d]pyrimidines have been the subject of study in recent years for their diverse bioactivity effects [2, 3]. In the present study, some novel pyrido [2,3-d]pyrimidine derivatives were synthesized through a green and efficient multicomponent procedure in the presence of a novel prepared LDH modified Clinoptilolite nanocatalyst. 4(6)-Aminouracil derivative, malononitrile, benzaldeyhyde derivatives were used as starting materials in the presence of the designed nanocatalysts in DMF as medium. This protocol has been previously reported under several reaction conditions . The reactions were carried out smoothly and the products were obtained with good to excellent yields within relative short reaction times. The nanocatalyst was easily separated by centrifugation from the reaction mixture. The products were simply obtained by aqueous dilution of the organic layer and washed with hot ethanol whenever necessary.
The analysis of nitroaromatic compounds such as nitrobenzene, nitrobenzaldehyde and nitrophenols in natural waters and its effluents has a major reputation for environmental control due to their appearance from a wide range of activities . Recently, so-called switchable hydrophilicity solvents (SHS) have been proposed as possible extraction solvents in liquid-liquid microextraction . Ahmar et al. investigated the behavior of the SHS  for the determination of nitroaromatic compounds. In this work, a novel approach is presented to determine 4- nitrobenzaldehyde in water samples. The procedure is based on pH assisted homogeneous liquid-liquid microextraction using a solvent having switchable hydrophilicity and then determination by differential pulse voltammetry at the surface of multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode. The extraction technique is based on the use of a water-immiscible solvent (N,NDipropylamine) that can be miscible upon the changes of pH of aqueous sample solution. Afterwards, phases separation is induced by the addition of sodium hydroxide. 4-nitrobenzaldehyde as a model compound was extracted from water samples into the N,N-Dipropylamine. Subsequently, the electrochemical behavior of 4-nitrobenzaldehyde has been studied on the MWCNTs modified glassy carbon electrode. Experimental parameters were optimized using a one-factor-at-a-time strategy. Under optimized conditions, a linear range was obtained between 1.5 and -1 -1 and -1, respectively. Finally, the performance of the proposed method was evaluated in river water as a real sample.
Recently, a new group of compounds, namely switchable hydrophilicity solvents (SHSs), has been introduced into the extraction field . In this study, a new pH assisted homogeneous liquid-liquid microextraction method based on SHSs followed by GC-MS detection has been developed for preconcentration and determination of polycyclic aromatic hydrocarbons (PAHs) in water samples. PAHs are important compounds because of their prevalence in the environment . The extraction technique makes use of 150 L of a water-immiscible solvent (Dipropylamine) that can be solubilized in the aqueous phase (6 mL) using HCl as a reagent. Afterwards, phases separation is induced by the addition of sodium hydroxide. The effects of operational parameters of the extraction were investigated and optimized. Under the optimum conditions, proposed method provided good linearity (1 ), low limits of ) and acceptable extraction repeatabilities (RSD% = 4.3-6.8). Finally, the proposed method allows the determination of the target analytes in different types of natural water samples and acceptable recoveries were obtained.
Hydrogen peroxide (H2O2) is widely used in food, medicine, cosmetics, industry, and water treatment applications [1-2]. It can be toxic at higher concentration because of the oxidizing and corrosive nature. In this work, a novel electrochemical sensor based on Cu/Fe layered double hydroxide@Fe3O4 nanoparticles has been successfully fabricated and used to H2O2 detection. The prepared LDH nanocomposite was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Then, the LDH nanocomposite was immobilized on glassy carbon electrode and its electrocatalytic activity for H2O2 reduction was studied. Factors which affect the electrocatalytic activity (modifier amount, pH of solution, and analysis time) have been investigated. Under the optimized conditions, the H2O2 the detection limit was found to be 3 μM (S/N = 3). Finally, the prepared sensor has been successfully applied to determine the H2O2 content in human urine samples.
Polychlorinated biphenyls (PCBs) are a class of synthetic organic compounds that are hazardous due to their chemical and thermal stability, hydrophobicity and toxic properties [1-2]. PCBs often exist at trace levels of concentration in the environment, so an effective pretreatment step is necessary for their preconcentration before quantification. In this study, a new method was successfully developed for the simultaneous determination of seven polychlorinated biphenyls in aqueous samples with switchable hydrophilicity solvent based liquid phase microextraction coupled to GC-MS detection. Triethylamine (TEA) was used as extraction solvent with switchable polarity, which can be miscible/immiscible upon the changes of pH of sample solution. The factors influencing the extraction efficiency, including type and volume of extraction solvent, pH and volume of aqueous sample, extraction time, and salt addition were investigated and optimized. Under the optimized conditions, good linearity (0.5-150 μg/L) and limits of detection (0.15 μg/L) were obtained for the PCBs by the proposed method. Also, the relative standard deviations (RSDs) were calculated between 5.2 and 6.4 %. In addition, enrichment factors (EFs) and extraction recoveries (ERs) were obtained in the ranges of 30.46-32.10 and 76.15-80.25 respectively. Finally, the proposed method was successfully applied for the analysis of PCBs in various water samples with excellent relative recoveries (RRs, 96.30-102.60).