Solid Phase Extraction and Simultaneous Spectrophotometric Determination of Trace Amounts of Copper and Iron Using Mixture of Ligands

 A novel sensitive and simple method for rapid and selective extraction, preconcentration and determination of iron (as its bathophenanthroline complex) and copper (as its neocuproine complex) using octadecyl silica cartridges and dual wavelength spectrophotometry is presented. The dual wavelength method (533 nm for the iron-bathophenanthroline and 454 nm for the copper-neocuproine as the analytical wavelength) is used to eliminate spectral interferences. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine, bathophenanthroline and hydroxylamine hydrochloride, type and least amount of eluent for elution of iron and copper complexes from cartridge, break-through volume and limit of detection are evaluated. The effects of various cationic and anionic interferences on percent recovery of iron and copper are also studied. Extraction efficiencies >95% are obtained by elution of cartridges with minimal amount of organic solvent. Iron and copper were determined in the range of 3–100 ng mL⁻¹. The limits of detection are 0.98 and 1.13 ng mL⁻¹ for iron and copper, respectively. The proposed method is applied successfully to the determination of both analytes in river, tap and well water samples. Author for correspondence. E-mail: yyamini@modares.ac.ir Received September 18, 2002; accepted December 12, 2002 Published online May 5, 2003     

HPLC and GC Methods for Determination of Lubricants and Their Evaluation in Analysis of Real Samples of Polyethylene

High performance liquid chromatography (HPLC) and gas chromatography (GC) are introduced for analysis of polymer lubricants (stearamide, oleamide and erucamide). In the HPLC method, a reverse phase octadecylsilane (ODS) column along with acetonitrile/methanol (60:40) as a mobile phase were used. Detection of analytes was performed by a UV detector at 202 nm. The analysis time was less than 8 min. In the GC method, polar capillary column and flame ionization detector (FID) were used for separations and detection, respectively. The analysis time by GC was longer than HPLC and was about 30 min. Limits of detection, linear range and repeatability of both methods are similar, but determination of oleamide in real samples by HPLC method is difficult due to complexity of the initial part of HPLC chromatogram in polyethylene samples. That problem is not observed in the GC method. Detection limits in both methods for all analytes are lower than 0.003% which are much lower than the amount of lubricants in commercial polymers (0.05–0.2%).     

Simultaneous Determination of Iron,Copper, and Cadmium by Adsorptive Stripping Voltammetry in the Presence of Thymolphthalexone

A novel, sensitive and selective adsorptive stripping procedure for simultaneous determination of iron, copper and cadmium is presented. The method is based on the adsorptive accumulation of thymolphthalexone (TPN) complexes of these elements onto a hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. The influences of control variables on the sensitivity of the proposed method for the simultaneous determination of iron, copper and cadmium were studied using the Derringer desirability function. The optimum analytical conditions were found to be TPN concentration of 2.0 μM, pH of 9.5, and accumulation potential at ?0.4 V vs. Ag/AgCl with an accumulation time of 60 s. The peak currents are proportional to the concentration of iron, copper and cadmium over the 1–80, 0.5–100 and 1–100 ng mL^?1 ranges with detection limits of 0.5, 0.4 and 0.9 ng mL^?1_, respectively. The R.S.D. at a concentration level of 20 ng mL^?1 of iron, copper and cadmium were 2.5%, 0.9% and 1.5% (n=6), respectively. The procedure was applied to the simultaneous determination of iron, copper and cadmium in the tap water and some synthetic samples with satisfactory results.     

An electropolymerized aniline-based fiber coating for solid phase microextraction of phenols from water

An aniline-based polymer was electrochemically prepared and applied as a new fiber coating for solid phase microextraction (SPME) of some priority phenols from water samples. The polyaniline (PANI) film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The efficiency of new coating was investigated using a laboratory-made SPME device and gas chromatography with flame ionization detection for the extraction of some phenols from the headspace of aqueous samples. The scanning electron microscopy (SEM) images showed the homogeneity and the porous surface structure of the film. The results obtained proved the ability of this polymer as a suitable SPME fiber coating for trapping the selected phenols. Influential parameters affecting the extraction process were optimized and an extraction time of 50 min at 50 °C gave maximum efficiency, when the aqueous sample was saturated with NaCl and adjusted at pH 2. This new coating can be prepared easily in a reproducible manner and it is rather inexpensive and stable against most of organic solvents. The PANI thickness can be precisely controlled by the number of CV cycles. At the optimum conditions, the R.S.D. for a double distilled water spiked with phenol and chlorophenols at ppb level were 4.8-17% (n = 3) and detection limits for the studied compounds were between 0.69 and 3.7 ng ml⁻¹, except for phenol and 4-chlorophenol. The optimized method was successfully applied to some real-life water samples.     

Thermodynamic simulation of performance of a dual cycle with stroke length and volumetric efficiency

This article presents finite-time thermodynamics analysis of an irreversible air standard dual cycle. An irreversible dual cycle model which is more close to practice is established. In this model, the effects of stroke length and volume efficiency by considering the nonlinear relation between the specific heats of working fluid and its temperature, the frictional loss, the internal irreversibility, and heat transfer loss are analyzed. The results show that if compression ratio is less than certain value, the power output increases with increasing stroke length, while if compression ratio exceeds certain value, the power output first increases and then starts to decrease with increasing stroke length. With further increase in compression ratio, the increase of stroke length results in decreasing the power output. The results also show that, throughout the compression ratio range, the power output increases with the increasing volumetric efficiency. The results obtained in this study are of importance to provide good guidance for performance evaluation and improvement of practical internal combustion engines.     

Application of a dispersive micro‐solid‐phase extraction method for pre‐concentration and ultra‐trace determination of cadmium ions in water and biological samples

A method for the trace determination of cadmium ions in water, human urine and human blood serum samples using ultrasonic‐assisted dispersive micro‐solid‐phase extraction (UA‐D‐μSPE) was developed. Silica‐coated magnetic nanoparticles were coated with polythiophene, and the resulting sorbent was characterized using thermogravimetry, differential thermal analysis, scanning electron microscopy, Fourier transform infrared spectrometry and X‐ray diffraction. Following UA‐D‐μSPE, cadmium ions were quantified using graphite furnace atomic absorption spectrometry. A Box–Behnken design was used for optimization of important sorption and desorption parameters in UA‐D‐μSPE: in the sorption step, pH of solution, sorption amount and sonication time for sorption; in the desorption step, concentration of eluent, volume of eluent and sonication time. The optimum conditions for the method were: pH of solution, 7.5; sonication time for sorption, 3 min; sorption amount, 35 mg; type and concentration of eluent, HCl and 1.1 mol l^?1; volume of eluent, 360 μl; sonication time for desorption, 110 s. Under the optimized conditions the limit of detection and relative standard deviation for the detection of cadmium ions by UA‐D‐μSPE were found to be 0.8 ng l^?1 and <6%, respectively.