Iranian Journal of Analytical Chemistry
Volume:1 Issue: 1, Winter and Spring 2014

In this work, an optical sensor for detection of ascorbic acid is described. The sensor is fabricated by casting and spin-coating silica sol-gel doped with 2,6-dichlorophenol indophenol on the glass plates. The sols are in turn obtained by acidic hydrolysis of various precursors such as tetraethoxysilane, triethoxymethylsilane and triethoxyoctylsilane in the presence of 2,6-dichlorophenol indophenol as dopant. Prepared sols then were coated on glass plates to form sol-gel films. UV-Vis spectrophotometric properties of 2,6-dichlorophenol indophenol doped in sol-gel films were studied and compared with in solution. At the optimum conditions the response of film to ascorbic acid is fast and linear in 0.07 – 3.34 mmol L-1 range. Detection limit and relative standard deviation of presented sensor for determination ascorbic acid were 0.05 mmol L-1 and 1.32 %, respectively.

In this work, a new, simple and fast method for the solid phase extraction-spectrophotometric determination of phosphate using cetyltrimethyl ammonium bromide immobilized on alumina-coated magnetite nanoparticles (CTAB@ACMNPs) has been developed. The determination of phosphate is based on the molybdenum blue method which was monitored at λmax of 810 nm. MNPs and ACMNPs characterized by SEM, VSM, and XRD spectroscopy. This method avoided the time-consuming column-passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. Under the optimal experimental conditions, the preconcentration factor (PF), detection limit (DL), linear range (LR) and relative standard deviation (RSD) of phosphate were 80 (for 400 mL of sample solution), 0.038 µg mL−1, 0.8-10.0 µg mL−1 and 2.5 % (for 5.0 µg mL-1, n=7), respectively. The proposed method was successfully applied to the separation/preconcentration and determination of phosphate in different water samples and suitable recoveries were obtained.

The electrochemical oxidation and determination of tryptophan (Trp) and glutathione (GSH) in the presence of catechol as a homogeneous redox in the aqueous medium were investigated at the surface of a carbon paste electrode modified with multi-walled carbon nanotube (MWCNT-CPE) using cyclic voltammetry (CV), double step potential chronoamperometry and differential pulse voltammetry (DPV) techniques. The results of differential pulse voltammetry showed two well-resolved anodic peaks for glutathione and tryptophan, which leads to voltammetric determination of each of them. The results shows the electrooxidation peak currents of GSH and Trp is linear in the concentration range of 2×10-6 M-5×10-5 M and 4×10-6 M-6×10-5 M, respectively. The kinetic parameters such as: the chemical reaction rate constant (kh) and transfer coefficient (α) were calculated 2.01×102 cm3 mol-1 s-1 and 0.31, respectively. Also, the apparent diffusion coefficient, Dapp, for GSH was found to be 1.95×10-6 cm2 s-1 in aqueous buffered solution. The proposed method was successfully applied for determination of glutathione and tryptophan in real sample using standard addition method.

This study propose a new analytical protocol for the determination of benzene, xylene, toluene and styrene in water samples using homogeneous liquid-liquid microextraction via flotation assistance (HLLME-FA) technique followed by gas chromatography-mass spectrometry (GC-MS). In this research, a special extraction cell was designed to facilitate collection of the low-density solvent extraction. No centrifugation was required in this procedure. The water sample solution was added into the extraction cell which contained an appropriate mixture of extraction and homogeneous solvents. By using air flotation, the organic solvent was collected at the conical part of the designed cell. The effects of different variables on the efficiency of the extraction were studied simultaneously using experimental design. Response surface methodology was applied to investigation the optimum conditions of each variable. Using optimized variables in the extraction process, for all target analytes, the detection limits, the precisions and the linearity of the method were found in the range of 0.8-8.2 ng mL-1, 3.09-7.96% (RSD, n=4) and 1-100 ng mL-1, respectively. The headspace method was used for the accuracy of comparison. The performance of the method was evaluated for extraction and determination of analytes in water samples and satisfactory results were obtained (RSD ≤10.06 %).

New, simple and cost effective spectrophotometric methods have been developed for the quality assessment of isoniazid (INH), in bulk and in pharmaceutical formulations by using novel reagents. The proposed methods involve the utility of ethyl 2-[(E)-(4-hydroxyphenyl) diazenyl]-3-oxobutanoate and benzil as novel reagents for the determination of INH. Developed methods are based on the condensation reaction of INH with reagents to give orange colored chromogen with an absorption band at 454 nm (for method A) and 436 nm (for method B). The applicability of these methods is demonstrated by the determination of the studied drug in commercial tablets and the results are statistically evaluated. The new procedures described in this paper are fast, convenient and have the novelty of carrying out the quantitative determination of INH in pure and in pharmaceutical formulation.

A simple, selective and efficient solid phase extraction method based on the use of  γ-alumina nanoparticles coated with sodium dodecyl sulfate (SDS) and modified with 2-​(5-​Bromo-​2-​pyridylazo)​-​5-​(diethylamino) ​phenol (5-Br-PADAP) as a new adsorbent was developed for the separation and preconcentration of trace amounts of manganese (II) prior to determination by flame atomic absorption spectrometry. Analytical influencing parameters including pH value, amount of modified sorbent, equilibrium time, volume and concentration of eluent were examined. Under the optimum conditions, adsorption capacity of nano- Al2O3-SDS-5-Br-PADAP, enrichment factor and limit of detection for manganese (II) was 18.5 mg g -1, 25 and 0.9 µg L -1, respectively. The procedure was successfully applied to the determination of manganese (II) in water and milk samples.

Cloud point extraction and spectrophotometric determination of trace quantities of cadmium in some vegetables have been developed. The research area for vegetables analysis was near to the Zarin Shahr where the soil received heavy metals from the Esfahan Steel Company. Cloud point extraction used dithizone as complexing agent and non ionic surfactant Triton-X114 as micellar phase. Several important variables affecting the separation and determination process were optimized. Under optimized conditions calibration graph was linear in the range of 1.0-180 ng mL-1 with detection limit of 0.2 ng mL-1. Preconcentration of 10 mL of samples gave an enhancement factor of 50. The proposed method was applied for determination of Cd(II) in vegetable samples with satisfactory results.

A complexometric method for the determination of titanium in the presence of other metal ions based on the selective masking ability of 5-sulphosalicylic acid towards titanium is described. Titanium (IV) present in a given sample solution is complexed with a known excess of EDTA and surplus EDTA is titrated against zinc sulphate solution at pH 5-6 using xylenol orange as the indicator. A known excess of 10% solution of 5-sulphosalicylic acid is then added. The mixture is then shaken well and the EDTA released from Ti-EDTA complex is titrated against the standard zinc sulphate solution. Reproducible and accurate results are obtained for 0.96 – 28.75 mg of titanium (IV) with relative error ± 0.17% and standard deviations ≤ 0.02 mg. The interference of various ions is studied. This method was applied to the determination of titanium (IV) in its alloys.

In this work, a selective method for separation and preconcentration of nickel ions at trace level on modified multiwalled carbon nanotubes columns and determination by flame atomic absorption spectrometry (FAAS) has been developed. Multiwalled carbon nanotubes were oxidized with concentrated HNO3 and then modified with loading 1-(2-pyridylazo)-2-naphtol. The sorption of Ni(II) ions was quantitative in the pH =9. Elution of the adsorbed nickel was carried out with 5.0 mL of 0.1 mol L−1 HNO3. The amount of eluted nickel was measured using flame atomic absorption spectrometry. Factors influencing sorption and desorption of Ni(II) ions were investigated, including the sample pH, flow rates of sample and eluent solution, eluent type, breakthrough volume and interference ions. The relative standard deviation of the method was ±0.57% (n=8) and the limit of detection was 2.04   g mL−1 (3σb/m, n=8). The method was applied to the determination of Ni(II) in water samples and standard alloy (NKK. NO. 920, Aluminum Alloy).