Voltammetric determination of nitrite by using a multiwalled carbon nanotube paste electrode modified with chitosan-functionalized silver nanoparticles.

A cyclic voltammetric method is described for the determination of nitrite by using a multiwalled carbon nanotube paste electrode (MWCNT) that was modified with chitosan-functionalized silver nanoparticles (Chit-AgNPs). The AgNPs were prepared by one step procedure using chitosan as stabilizing agent. The resulting modified AgNPs were drop-coated onto the electrode. By combining the advantages of chitosan, AgNPs (in the form of Chit-AgNPs) and MWCNT, the assay exhibits a remarkable improvement in the cyclic voltammetric response towards the oxidation of nitrite at a typical peak potential of 0.81 V (vs. SCE) in buffer of pH 4.0. The accumulation of nitrite on the electrode also was achieved, and this further enhances the analytical sensitivity. Under optimized conditions, the oxidation peak current increases linearly in the 100 nM to 50 µM nitrite concentration range, and the detection limit is 30 nM. The method has high selectivity for nitrite even in the presence of other potentially interfering ions. Graphical abstract Schematic illustration of the prepared chitosan functionalized silver nanoparticles (transmission electron microscope image) and modification of multi-walled carbon nanotube paste electrode with chitosan functionalized silver nanoparticles for the electrochemical oxidation of nitrite to nitrate.

Nonenzymatic amperometric dopamine sensor based on a carbon ceramic electrode of type SiO2/C modified with Co3O4 nanoparticles.

An amperometric nonenzymatic dopamine sensor has been developed. Cobalt oxide (Co3O4) nanoparticles were uniformly dispersed inside mesoporous SiO2/C. A sol-gel process was used for the preparation of this mesoporous composite material (SiO2/C). This mesoporous composite has a pore size of around 13-14 nm, a large surface area (SBET 421 m2·g-1) and large pore volume (0.98 cm3·g-1) as determined by the BET technique. The material compactness was confirmed by SEM images which showing that there is no phase segregation at the magnification applied. The chemical homogeneity of the materials was confirmed by EDX mapping. The SiO2/C/Co3O4 nanomaterial was pressed in desk format to fabricate a working electrode for nonenzymatic amperometric sensing of dopamine at a pH value of 7.0 and at a typical working potential of 0.25 V vs SCE. The detection limit, linear response range and sensitivity are 0.018 µmol L-1, 10-240 µmol L-1, and 80 µA·µmol L-1 cm-2, respectively. The response timé of the electrode is less than 1 s in the presence of 60 µmol L-1 of dopamine. The sensor showed chemically stability, high sensitivity and is not interfered by other electroactive molecules present in blood. The repeatability of this sensor was evaluated as 1.9% (RSD; for n = 10 at a 40 µmol L-1 dopamine level. Graphical abstract Schematic presentation of the preparation of a nanostructured composite of type SiO2/C/Co3O4 for electrooxidative sensing of dopamine.

Simultaneous assessment of zinc, cadmium, lead and copper in poultry feeds by differential pulse anodic stripping voltammetry.

In the present work four metals (Zn, Cd, Pb and Cu) were determined simultaneously in 28 commercial broiler poultry feeds by differential pulse anodic stripping voltammetry (DPASV) using hanging mercury drop electrode (HMDE). The digestion of poultry feeds was carried out with concentrated nitric acid and hydrogen peroxide (2:1) with the help of microwave heating. Acetate buffer of pH 5 was used as a supporting electrolyte. The limit of detection for Zn, Cd, Pb and Cu was 0.69, 0.35, 0.68 and 0.24 microg/kg, respectively. The amount of Zn, Cd, Pb and Cu in the analyzed poultry feeds was ranged between 54.3-482.2, 3.8-33.6, 23.2-32.6 and 12.3-65.8 mg/kg, respectively. In most of analyzed poultry feed samples, the amount of Cd and Pb was found to be greater than the maximum tolerable level (MTL) which could be harmful for the poultry.

The correlation of arsenic levels in drinking water with the biological samples of skin disorders.

Arsenic (As) poisoning has become a worldwide public health concern. The skin is quite sensitive to As and skin lesions are the most common and earliest nonmalignant effects associated to chronic As exposure. In 2005-2007, a survey was carried out on surface and groundwater arsenic contamination and relationships between As exposure via the drinking water and related adverse health effects (melanosis and keratosis) on villagers resides on the banks of Manchar lake, southern part of Sindh, Pakistan. We screened the population from arsenic-affected villages, 61 to 73% population were identified patients suffering from chronic arsenic toxicity. The effects of As toxicity via drinking water were estimated by biological samples (scalp hair and blood) of adults (males and females), have or have not skin problem (n=187). The referent samples of both genders were also collected from the areas having low level of As (<10 microg/L) in drinking water (n=121). Arsenic concentration in drinking water and biological samples were analyzed using electrothermal atomic absorption spectrometry. The range of arsenic concentrations in lake surface water was 35.2-158 microg/L, which is 3-15 folds higher than World Health Organization [WHO, 2004. Guidelines for drinking-water quality third ed., WHO Geneva Switzerland.]. It was observed that As concentration in the scalp hair and blood samples were above the range of permissible values 0.034-0.319 microg As/g for hair and <0.5-4.2 microg/L for blood. The linear regressions showed good correlations between arsenic concentrations in water versus hair and blood samples of exposed skin diseased subjects (R2=0.852 and 0.718) as compared to non-diseased subjects (R2=0.573 and 0.351), respectively.

A new simple sensitive differential pulse polarographic method for the determination of acrylamide in aqueous solution.

A new simple sensitive differential pulse polarographic (DPP) method was investigated for the determination of acrylamide (AA) directly in a neutral aqueous solution. The AA showed a well-defined and well-resolved peak in pure aqueous LiCl at -1.84V in the potential range from -1.6V to -1.97V at nitrogen pressure of 0.5kgcm(-2). Among the various electrolytes studied, the AA showed good DPP response in the presence of LiCl and tetra methyl ammonium iodide, while it showed poor response in the presence of tetra butyl ammonium hydroxide and tetra butyl ammonium bromide due to their strong adsorption on the surface of electrode which hindered its reduction. The effect of LiCl concentration, the cyclic voltammetric response and the drop time study showed that AA exhibited an irreversible adsorptive electrochemical behavior. The good electrochemical response in pure aqueous medium suggested that hydrogen bonding might be involved which may favor the electrode reaction. Under optimized conditions, the peak current was linear in the entire concentration range from 0.2 mgL(-1) to 20 mgL(-1) with the correlation coefficient of R(2)=0.9998. The method showed good reproducible results with R.S.D. of 0.3% (n=16). The detection limit (LOD) was 27 microgL(-1). The influence of various interfering agents was also studied. The method was applied successfully for the quantification of AA in water samples without any interference effect from alkali metals.

Simpler spectrophotometric assay of paracetamol in tablets and urine samples.

A very fast, economical and simpler direct spectrophotometric method was investigated for paracetamol (PC) determination in aqueous medium without using any chemical reagents. The method is based on the photo-absorption of the analyte at 243 nm after dissolution in water. The change in structure of PC after addition of water was studied by comparing the corresponding FTIR spectra. Optimization studies were conducted by using a 5 microg ml(-1) standard solution of the analyte. Various parameters studied include, time for stability and measurement of spectra, effect of HCl, NaOH, CH(3)COOH and NH(3) for change in absorbance and shift in spectra, interference by some analgesic drugs and some polar solvents and temperature effect. After optimization, Beer's law was obeyed in the range of 0.3-20 microg ml(-1) PC solution with a correlation coefficient of 0.9999 and detection limit of 0.1 microg ml(-1). The newly developed method was successfully applied for PC determination in some locally available tablets and urine samples. The proposed method is very useful for quick analysis of various types of solid and liquid samples containing PC.

Electrolytic recovery of chromium salts from tannery wastewater.

Tannery wastewater collected from a local leather industry in Peshawar, Pakistan was subjected to DC electrolysis in a simple cell having two static sheet electrodes and stirring assembly after proper dilution and adjustment to desired conditions. One percent HNO(3) and 1% NaHCO(3) were used as electrolytes and pH adjusters. The latter salt also worked as sodium source for anodic deposition of Na(2)Cr(2)O(7). Various combinations of electrodes were tested and conditions optimized for best electrode couple with increased recovery and removal of chromium in the form of Cr(OH)(3) and/or Na(2)Cr(2)O(7) at cathode and anode, respectively. The recovery of 99% chromium was achieved after 2h electrolysis at a cell potential of 1.0 V, pH 5.0 and stirring rate of 500 rpm using Pb sheet as anode and Cu sheet as cathode. The most interesting and novel finding of this work was the recovery of the mentioned salt(s) alone at Cu cathode or Pb anode or collectively at both electrodes by proper control of pH. Such treatment not only minimizes the environmental water pollution, but results in the formation of useful products employed for recycling purpose in tannery or other related industry to make the process economical.

Ultra-trace level determination of hydroquinone in waste photographic solutions by UV-vis spectrophotometry.

A simpler UV-vis spectrophotometric method was investigated for hydroquinone (HQ) determination using KMnO(4) as oxidizing agent for conversion of HQ to p-benzoquinone (BQ) as well as signal enhancer. Various parameters such as analytical wavelength, stability time, temperature, pH, solvent effect and interference of chemicals were checked and parameters optimized by using 1mugml(-1) standard solution of HQ. Beer's Law was applicable in the range of 0.07-2mugml(-1) and 0.005-0.05mugml(-1) at 245.5nm and at 262nm for aqueous standard solutions of HQ with linear regression coefficient value of 0.9978 and 0.9843 and detection limit of 0.021mugml(-1) and 0.0016mugml(-1) HQ, respectively. Standard deviation of 1.7% and 2.4% was true for 1mugml(-1) and 0.03mugml(-1) HQ solution (n=11) run at respective wavelengths. The method was successfully applied to dilute waste photographic developer samples for free HQ determination.