Analytical and Bioanalytical Chemistry Research
Volume:3 Issue: 2, Summer - Autumn 2016

Formaldehyde in small quantities is commonly analyzed by spectrophotometric methods. One of the most-commonly used spectrophotometric techniques for this purpose is based on the reaction with chromotropic acid. Because of its simplicity, sensitivity, selectivity and its low cost, it is still widely used. Investigations for replacing the concentrated sulfuric acid with other acids or using more dilute solutions of sulfuric acid have been performed. Herein, spectrophotometric determination of formaldehyde by chromotropic acid in the sulfuric acid medium is explored and modified by response surface methodology. The reaction was monitored by measuring the absorbance of the product at 574 nm. The factors affecting the response, i.e. concentration of sulfuric acid and concentration of chromotropic acid, were explored and optimized using response surface methodology. The calibration curve was linear in the range of 0.03-7.00 mg l-1 with detection limit of 0.005 mg l-1. The method was found to be sensitive, selective and was applied to determine the formaldehyde in toothpaste, clothing softener and acetic acid samples with satisfactory results.

In this study, the trace amounts of erythrosine, as a food dye is determined by cloud point extraction-scanometry (CPE-Scanometry) as a new, facile, available, fast, sensitive, and low cost method. The method is based on the CPE of analyte from aqueous solution, diluting the extracted surfactant-rich phase with ethanol, transfer to Plexiglas®cell and scanning the cells containing the analyte solution with a scanner and measuring the RGB parameters with software written in visual basic (VB6) media. The parameters such as pH of the system, the concentration of the surfactant, equilibration temperature and time were optimized. In addition, the effects of some foreign species were investigated. The linear range for the proposed method and CPE-Spectrophotometry are 0.067-5.330 µg ml-1 and 0.030-3.000 µg ml-1, respectively. The results of the proposed method were comparable with those of CPE-Spectrophotometry. The method was successfully applied to the determination of erythrosine in food samples.

Oscillating reactions are one of the most interesting topics in chemistry and analytical chemistry. Fluctuations in concentrations of one the reacting species (usually a reaction intermediate) create an oscillating chemical reaction. In oscillating systems, the reaction is far from thermodynamic equilibrium. In these systems, at least one autocatalytic step is required. Developing an instinctive feeling for how oscillating reactions work will be invaluable to future generations of chemists. Some software programs have been released for simulating oscillating systems; however, the algorithm details of such software are not transparent to chemists. In contrast, function of spreadsheet tools, like Microsoft Excel, is well understood, and the software is nearly universally available. In this work, the simulation and visualization of different oscillating systems are performed using Microsoft excel. The simple repetitive solving of the ordinary differential equation of an autocatalytic reaction (a spreadsheet row) followed by time, easily automated by a subroutine (a “Macro” in Excel), readily simulates an oscillating reaction. This permits the simulation of some oscillating systems such asBelousov-Zhabotinsky. The versatility of an easily understandable computational platform further enables the simulation of the effects of linear and nonlinear parameters such as concentrations of reactants and catalyst, and kinetic constants. These parameters are readily changed to examine their effects.

A chemically modified carbon paste electrode with 2-chlorobenzoyl ferrocene (2CBF) and carbon nanotube (2CBFCNPE) was employed to study the electrocatalytic oxidation of ascorbic acid in aqueous solution using cyclic voltammetry, square wave voltammetry and chronoamperometry. The diffusion coefficient (D = 1.42 × 10-6 cm2 s-1), and the kinetic parameter such as the catalytic rate constant (k = 3.7 × 10 3 M-1 s-1) of ascorbic acid oxidation at the surface of 2CBFCNPE were determined using electrochemical approaches. It has been found that under an optimum condition (pH 4.0), the oxidation of ascorbic acid at the surface of such an electrode occurs at a potential about 85 mV less positive than that of an unmodified carbon paste electrode. Applying square wave voltammetry, in phosphate buffer solution (PBS) of pH 4.0, the oxidation current increases linearly with two concentration intervals of ascorbic acid, one is 1.0 × 10-7-2.5 × 10-6 M and the other is 2.5 × 10-6-7.0 × 10-5 M. Detection limit (3δ) was obtained 64.0 nM. This method was also examined for determination of ascorbic acid in some real samples.

This article presents the method of extraction-preconcentration of Lead, Cadmium, and Nickel ions from food samples using the Ghezeljeh montmorillonite nanoclay (Geleh-Sar-Shoor) as a new native adsorbent in batch single component systems. The extraction-preconcentration of heavy metals were carried out by applying the solid phase extraction (SPE) method followed by atomic absorption spectroscopy (AAS), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES). The Ghezeljeh nanoclay was characterized by using Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy-energy dispersive spectrometer operating (SEM-EDS), X-ray diffractometry (XRD), X-ray fluorescence (XRF), Cation Exchange Capacity (CEC) measurements, BET specific surface area and Zeta potential. According to BET theory, the specific surface areas of the Ghezeljeh nanoclay was calculated to be 19.8 m2 g-1 whereas the cation exchange capacity was measured to be 150 meq/100 g. The results of XRD, XRF, FT-IR, Zeta potential and BET surface area of the nanoclay confirmed that montmorillonite was the dominant mineral phase. Based on SEM images of this clay, it can be seen that the distance between the plates is nm level. For all three ions, the detection and quantification limits, dynamic linear range, preconcentration factor, and adsorption capacity were obtained. The effect of various interfering ions was studied. The experimental method was successfully applied for the extraction of heavy metals in different tea and rice samples.

A modified electrode was prepared by modification of the carbon paste electrode (CPE) with graphene nano-sheets. The fabricated modified electrode exhibited an electrocatalytic activity toward gallic acid (GA) oxidation because of good conductivity, low electron transfer resistance and catalytic effect. The graphene modified CPE had a lower overvoltage and enhanced electrical current respect to the bare CPE for the oxidation of GA. The oxidation potential of GA decreased more than 210 mV by the modified electrode. The modified electrode responded to the GA in the concentration range of 3.0 × 10-5-1.5 × 10-4 M with high sensitivity by the technique of differential pulse voltammetry. Also, detection limit of 1.1 × 10-7 M was obtained by this modified electrode for GA. This electrode was used for the successful determination of GA in plant samples. Therefore, the content of total polyphenols in plant samples can be determined by the proposed modified electrode based on the concentration of GA in the sample.

The adsorption characteristics of riboflavin onto silver-deposited iron oxide magnetic nanoparticles (Ag/Fe3O4) have been described. Characterization of the synthesized Ag/Fe3O4 nanoparticles was achieved by FTIR spectra, TEM image and XRD pattern. The influence of several experimental parameters such as nanoparticles dosage, pH of the sample solution, different orientations of the riboflavin molecules toward Ag/Fe3O4 surface, riboflavin concentration, contact time of the reagents, temperature, ionic strength and presence of halide anions were studied. Experimental data indicated that Ag/Fe3O4 nanoparticles adsorb more than 90% of riboflavin under the optimum experimental conditions of the adsorbent dosage of 4.0 mg, a pH of 6.0, and a contact time of 2.0 min, when an initial riboflavin concentration of 0.02 mM is used. The results revealed that the presence of halide anions lower the adsorption of riboflavin on the surface of nanoparticles due to dissolution of the silver layer of the nanoparticles. It was found that the adsorption isotherm is best fitted to Dubinin-Radushkevich and Freundlich models and kinetic model followed a pseudo-second-order adsorption rate.

An air–assisted liquid–liquid microextraction method for the extraction and preconcentration of trace amounts of some synthetic phenolic antioxidants in biological fluids followed by their determination by gas chromatography–flame ionization detection has been reported. In this method the target analytes are extracted into a few microliters of carbon tetrachloride (extraction solvent) from an aqueous solution by aspirating and dispersing the extraction solvent and sample solution mixture by a syringe. After extraction, phase separation is performed by centrifugation and the enriched analytes in the sedimented phase are determined. The parameters affecting the extraction efficiency including the type and volume of extraction solvent, salt addition, extraction times, and pH are investigated in details. Under the optimum extraction conditions, the method shows low limits of detection and quantification between 0.8–1.8 and 2.7-5.6 ng mL–1, respectively. The method is applied to determine some phenolic antioxidants in biological samples and extraction recoveries are ranged from 63 to 81%. Enrichment factors are obtained between 315 and 405. The method shows good linearities in the range of 3–6000 ng mL-1 with the correlation coefficients higher than 0.996. Relative standard deviations are lower than 8% for intra-day (n=6) and inter-day (n=4) precisions. Finally the proposed method is successfully used for determination of the analytes in urine and plasma samples.

In this research,QSAR study has been carried out on quinolizidinyl derivatives as potent inhibitors of Acetyl and Butyrylcholin esterase in Alzheimer’s disease. Despite significant research efforts in both industry and academia, there are currently no diseases modifying therapies available to treat this illness. Significant evidence suggests that the pathology of AD is linked to generation of β-amyloid peptides (Aβ) through proteolytic processing of amyloid precursor protein (APP). Genetic algorithm (GA), Jack-Knife and stepwise multiple linear regressions (stepwise-MLR) were used to create non-linear and linear QSAR models. The root-mean square errors of the training set and the validation set for GA–ANN model using Jack-Knife method, were 0.1406, 0.2165 and R2 was 0.90. Also, the R and R2 values in the gas phase were obtained as 0.88 and 0.78 from GA-stepwise MLR model, respectively. Also, we suggest that compounds No.4, 6, 10, 14, 24, 26 and 34 have the most appropriate structure for the design of drugs to pharmacists. Electronegativities, atomic polarizability and atomic van der Waals volumes were important descriptors in our study. Geometry optimization of compounds was carried out using the B3LYP method employing a 6–31G (d) basis set.

A chemiluminescence (CL) method has been developed for the determination of Hydroxyzine (Hyd) and its metabolite Cetirizine (Cet). The method is based on sensitizing effect of Cet and Hyd on the weak CL reaction between Ru(phen)32 and acidic Ce(IV). A mechanism for the CL reaction has been proposed on the basis of UV-Vis, fluorescent and CL spectra. By using the recommended procedure, the calibration graphs were linear over 0.14 to 14.0 μg mL-1 (r2=0.9966) and 0.07 to 10.0 μg mL-1 (r2=0.9984) for Hyd and Cet, respectively. The limits of detections were 0.06 μg mL-1 and 0.03 μg mL-1 for Hyd and Cet, respectively. The percent of relative standard deviations (n=11) for 1.0 μg mL-1 of Hyd and 0.74 μg mL-1 of Cet were 4.5 and 2.3%, respectively. The broad time profile of Hyd and Cet allowed us to determine Hyd contents in plasma samples with minimum blank interferences from cysteine and ascorbic acid. The method has been satisfactorily used for the determination of Hyd and Cet in syrups, tablets and human plasma.

This paper reports on synthesis of a magnetic adsorbent for wastewater treatment purposes. In this regard, platanus orientalis waste leaves were chosen as a cheap material for preparing the magnetic adsorbent by loading magnetite nanoparticles on it. The synthesized adsorbent was characterized using scanning electron microscope and X-ray diffractometer. Then, it was used for magnetic solid phase extraction and removal of five cationic dyes including methyl violet (MV), methylene blue (MB), malachite green (MG), crystal violet (CV), and neutral red (NR) from aqueous solution as a model application. Different important factors affecting the adsorption process were optimized, and the results showed that under the optimized conditions (pH 10 for CV, MV, MB, and MG; pH 6 for NR; adsorbent dosage, 20 mg; agitation time, 25 min) efficient removal of the investigated dyes (adsorption capacities between of 89-133 mg g-1) is achievable using the synthesized adsorbent. Furthermore, the reusability experiments showed that the adsorbent could be reused at least ten cycles without any significant loss in its sorption behavior.

In this study, amine functionalized Kit-6 silica mesoporous magnetite nanocomposite (NH2-MMNC) was synthesized by chemical methods and used as an efficient and recoverable adsorbent for removal of Ponceau 4R, as a toxic dye, from aqueous solutions. The synthesized nanocomposites were characterized by XRD, FT-IR, BET and SEM instruments. The effect of various experimental parameters on the dye removal efficiency was studied using Taguchi orthogonal array design (L9 array) method and under optimum conditions (pH = 2, adsorbent amount = 80 mg, stirring time = 30 min and without addition of salt) removal efficiency higher than 98% was obtained.The kinetic studies showed rapid sorption dynamics by a second-order kinetic model with R2=0.9993 and qeq= 58.8 mg g-1, suggesting chemisorption mechanism. Dye adsorption equilibrium data were fitted well to the Langmuir isotherm and the synthesized sorbent showed complete removal efficiency. The maximum monolayer capacity of the sorbent (Qmax , mg g-1), and the Langmuir binding constant which is related to the energy of adsorption (KL, L mg-1), were obtained as 87.7 and 0.407, respectively. The results of real samples show that the synthesized nanocomposite can be used as a recyclable and efficient adsorbent for removal of Ponceau 4R anionic dye from aqueous solutions.