Payman Hashemi

Amino ethyl-functionalized nanoporous silica as a novel fiber coating for solid-phase microextraction

Nanoporous silica (SBA-15) was prepared and functionalized with 3-[Bis(2-hydroxyethyl)amino] propyl-triethoxysilane (HPTES) to be used as a highly porous fiber coating material for solid-phase microextraction (SPME). The prepared HPTES-SBA-15 particles had a lengthy morphology and a specific surface area of 790 m(2) g(-1). They were characterized by N(2) sorption analyses, scanning electron microscopy and thermogravimetric analysis. The prepared nanomaterial was immobilized onto a copper wire for fabrication of the SPME fiber. The fiber was evaluated for the extraction of BTEX and some phenolic compounds in combination with GC-MS. For optimization of factors affecting the extraction efficiency of the phenolic compounds, a simplex optimization method was used. The proposed fiber showed some selectivity towards the polar phenolic compounds with extraction efficiencies better than a PDMS commercial fiber. The repeatability for one fiber (n=5), expressed as relative standard deviation (RSD), was between 6.5% and 9.8% and the reproducibility for five prepared fibers was between 8.2% and 11.3% for the test compounds. No significant change was observed in the extraction efficiency of the new SPME fiber over 50 extractions. The fiber was successfully applied to the determination of phenolic compounds in spiked river water and sewage samples. Thus, HPTES-SBA-15 fiber is a promising alternative to the commercial fibers as it is robust, selective, highly porous and easily and inexpensively prepared.

Development of a simple device for dispersive liquid-liquid microextraction with lighter than water organic solvents: Isolation and enrichment of glycyrrhizic acid from licorice

A simple device was developed that makes the use of lighter than water organic solvents feasible in dispersive liquid-liquid microextraction (DLLME) method. In the ordinary DLLME, the fact that a heavier than water organic solvent must be used, to be sedimented at the conical bottom of a centrifuge tube, limits the applications of this method in some extent. In the developed method, a glass tube with a narrow neck is inserted inside the centrifuge tube. After phase separation, the organic solvent is accumulated in the narrow neck of the device and therefore, can be simply collected by a micro-syringe. The DLLME method with the proposed device was tested for the enrichment of glycyrrhizic acid from aqueous extracts of licorice before analysis by a HPLC method. n-Hexanol and acetone were used as the organic and disperser phases, respectively. Effects of pH, salt concentration and phase volumes on the extraction of the analyte were optimized using a central composite (response surface) design. Under the optimized conditions (i.e. pH 1.3, ionic strength 0.2 mol L(-1), n-hexanol 140 microL and acetone 0.8 mL) an extraction recovery of 104.1 (+/-5.1)% and an enrichment factor of 54 were obtained. The proposed method was successfully applied for the study of glycyrrhizic acids level of licorice roots grown in three regions of Lorestan province, Iran, with different climate conditions.

Homogeneous liquid-liquid extraction method for the selective separation and preconcentration of ultra trace molybdenum

A new simple and efficient homogeneous liquid-liquid extraction method for the selective separation and preconcentration of molybdenyl ions was developed. alpha-Benzoin oxime (ABO) was investigated as a complexing ligand, and perfluorooctanoate ion (PFOA(-)) was applied as a phase-separator agent under strongly acidic conditions. Under the optimal conditions ([ABO]=2.1x10(-3)M, [PFOA(-)]=1.8x10(-2)M, [HNO(3)]=1.7M, [acetone]=11.8% (v/v)), 10mug of molybdenum in 5ml aqueous phase could be extracted quantitatively into 40mul of the sedimented phase. The maximum concentration factor was 125-fold. Thiocyanate was applied as a chromogenic reagent for the direct spectrophotometric determination of molybdenum in the sedimented phase. The reproducibility of the proposed method is at the most 2.4%. The influence of the type and concentration of acid solution, the concentration of ABO, the type and volume of the water-miscible organic solvent, the concentration of PFOA(-), and the effect of different diverse ions on the extraction and determination of molybdenum(VI) were investigated. The proposed method was applied to the extraction and determination of molybdenum(VI) in natural water, Spinach, and Lucerne samples. A satisfactory agreement exists between the results obtained by the proposed method and those reported by GF-AAS.

Reversed-phase dispersive liquid–liquid microextraction with central composite design optimization for preconcentration and HPLC determination of oleuropein

A reversed-phase dispersive liquid-liquid microextraction (RP-DLLME) method was developed for the preconcentration and direct HPLC determination of oleuropein in olives processing wastewater (OPW) and olive leaves extracts. In conventional DLLME, the sedimented phase is a micro-drop of a chlorinated organic solvent that is not compatible with RP-HPLC. Therefore, solvent evaporation and reconstitution with an appropriate solvent is often required. In RP-DLLME, this problem was overcome by overturning the solvent polarity in the ordinary DLLME and replacing the organic solvent with water. A central composite chemometrics design was used for multivariate optimization of the effects of five different parameters influencing the extraction efficiency of the method. In the optimized conditions, a mixture of 1.4 mL of an ethyl acetate extract of sample and 40 microL water (pH 5.0) was rapidly injected into 5.3 mL of cyclohexane. After centrifugation of the formed cloudy mixture, a micro-drop of the aqueous phase was sedimented at the conical bottom of the centrifuge tube. This phase, that contained the preconcentrated and partially purified analyte, was directly injected into an RP-HPLC column for analysis. A mean extraction recovery of 102.5 (+/-4.5) % with enrichment factors exceeding 38, was obtained for five replicated analysis. The detection limit of the method (3 sigma) for OE was 0.02 microg L(-1) for OPW and 2 x 10(-3) mg kg(-1) for olive leaves samples. The results showed that, RP-DLLME is a promising technique which is quick, easily operated and can be directly coupled to HPLC.

A new Schiff's base ligand immobilized agarose membrane optical sensor for selective monitoring of mercury ion

A highly selective optical sensor was developed for the Hg(2+) determination by chemical immobilization of 2-[(2-sulfanylphenyl)ethanimidoyl]phenol (L), on an agarose membrane. Spectrophotometric studies of complex formation between the Schiffs base ligand L and Hg(2+), Sr(2+), Mn(2+), Cu(2+), Al(3+), Cd(2+), Zn(2+), Co(2+) and Ag(+) metal ions in methanol solution indicated a substantially larger stability constant for the mercury ion complex. Consequently, the Schiffs base L was used as an appropriate ionophore for the preparation of a selective Hg(2+) optical sensor, by its immobilization on a transparent agarose film. A distinct color change, from yellow to green-blue, was observed by contacting the sensing membrane with Hg(2+) ions at pH 4.5. The effects of pH, ionophore concentration, ionic strength and reaction time on the immobilization of L were studied. A linear relationship was observed between the membrane absorbance at 650 nm and Hg(2+) concentrations in a range from 1×10(-2) to 1×10(-5) mol L(-1) with a detection limit (3σ) of 1×10(-6) mol L(-1). No significant interference from 100 times concentrations of a number of potentially interfering ions was detected for the mercury ion determination. The optical sensor was successfully applied to the determination of mercury in amalgam alloy and spiked water samples.

CMK-3 nanoporous carbon as a new fiber coating for solid-phase microextraction coupled to gas chromatography-mass spectrometry.

CMK-3 nanoporous carbon was prepared and characterized as a highly porous fiber coating, with a highly ordered carbon framework, for solid-phase microextraction (SPME). The nanomaterial was immobilized onto platinum, stainless steel and copper metal wires for preparation of new SPME fibers. The copper-CMK-3 fiber showed superior properties and therefore was applied for extraction of some phenolic compounds in combination with GC-MS. For optimization of the extraction conditions, a simplex optimization method was used. The selected conditions were: sample volume 13 ml, extraction temperature 56°C, extraction time 7 min, ultrasonic time 5.5 min, pH 5 and salt concentration 8.9%. The selected fiber showed some selectivity towards the polar phenolic compounds and its extraction efficiency was better than a commercial PDMS fiber. Linear calibration curves with correlation coefficients better than 0.99 and detection limits in the range from 0.002 to 0.068 μg mL(-1) were obtained for the fiber. No significant change was observed in the extraction efficiency of the new SPME fiber over at least 40 extractions. The fiber was successfully used for the determination of phenolic compounds in natural water samples.

Factorial design for optimization of experimental variables in preconcentration of copper by a chromotropic acid loaded Q-Sepharose adsorbent

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5ml portion of a 0.02moll(-1) HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18moll(-1) sodium nitrate in the matrix. A 5ml portion of a 0.02moll(-1) CTA was sufficient for loading of a 0.5ml column prior to preconcentration of copper from a 150ml sample solution. Matrix ions of Ca(2+), Mg(2+), Na(+) and K(+) and potentially interfering ions of Pb(2+), Ni(2+), Cd(2+), Co(2+), Zn(2+) and Mn(2+) with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0mugl(-1) was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.

Equilibrium and kinetic properties of a fast iminodiacetate based chelating ion exchanger and its incorporation in a FIA-ICP-AES system

The equilibrium and kinetic properties of an iminodiacetate (IDA) based chelating ion exchanger with a crosslinked agarose, Novarose, as support has been investigated. The second and third acidity constants and some complexation constants of the ligand were determined for adsorbents with metal binding capacities of 140, 55 and 18 micromol ml(-1), respectively. The adsorbent of medium capacity showed fast adsorption and desorption of Cu(II), Cd(II), Ni(II) and Ca(II) both in the batch and column mode. It was found to be about 50 times faster than Chelex-100 (50-100 mesh) in accumulation of these metal ions in the batch mode. Studies of the adsorbent in a flow system, using a 5 mm x 6 mm i.d. column, indicated quantitative accumulation of Cu(II), Cd(II), and Ni(II) at volumetric flow rates up to 110 ml min(-1). Linear calibration curves with r > 0.999 and signal enhancement factors up to 1300 were obtained. Preconcentration by a FIA system connected to an ICP-AES instrument will make simultaneous measurement of ultratrace concentrations of a number of metal ions possible within reasonable cycle times due to the high flow rates which can be used with the adsorbent. Trace amounts of cadmium and copper in tap water were determined successfully at 60 ml min(-1). However, copper and nickel in tap water are strongly complexed and do not accumulate quantitatively even at low flow rates. Hence a sample pretreatment is needed. Copper was completely adsorbed after UV-treatment of the sample.

A dual column system using agarose-based adsorbents for preconcentration and speciation of chromium in water.

Three different agarose-based chelating adsorbents with, respectively, iminodiacetic acid (IDA), tris(2-aminoethyl)amine (TREN) and dipicolylamine (DPA) functional groups and an agarose-based anion exchanger (Q-Sepharose), were studied for the separation and preconcentration of Cr(III) and Cr(VI) species in water. Column recoveries of all the adsorbents were plotted against pH, and it was found that at pH 3.0 the IDA adsorbent selectively adsorbs Cr(III), with a 100 +/- 1.0% recovery. The Q-Sepharose, on the other hand, accumulated only Cr(VI) at this pH, again with a recovery of 100 +/- 1.0%. A dual column system was accordingly designed, using the two adsorbents in tandem, for the separation and preconcentration of the chromium species. The effects of pH, sample flow rate, column length, eluent type, eluent volume, acid concentration and interfering ions on the recoveries of Cr(III) and Cr(VI) were carefully studied. It was shown that by passing test solutions, at pH 3.0; through the dual column system, the two chromium species could be individually collected on the columns, respectively, and eluted, one after the other. A portion of 2moll(-1) hydrochloric acid was used for elution of each column before final measurement by flame AAS method. A preconcentration factor of 12, a detection limit of 7.7 +/- 0.1mugl(-1) and a precision expressed as relative standard deviation of 0.4% (at 0.3mgl(-1)) were achieved for six replicates. Application of the developed method to the determination of chromium species in spiked river and tap water and wastewater samples, from a dye production plant, resulted in excellent agreements with accepted concentrations.

Selective dispersive liquid–liquid microextraction and preconcentration of Ni(II) into a micro droplet followed by ETAAS determination using a yellow Schiff's base bisazanyl derivative

A simple, rapid and sensitive method was developed for the selective separation and preconcentration of Ni(II) using dispersive liquid-liquid microextraction, by a yellow Schiffs base bisazanyl derivative, as a selective complexing agent. In this method, a mixture of 45 μL chloroform (extraction solvent) and 450 μL tetrahydrofuran (dispersive solvent) is rapidly injected by syringe into a 5 mL aqueous sample containing 3% (w/v) sodium chloride and an appropriate amount of the Schiffs base. As a result, a cloudy solution is formed by entire dispersion of the extraction solvent into the aqueous phase. After centrifuging for 5 min at 5000 rpm, the sedimented phase is directly injected into the electrothermal atomic absorption spectrometry for Ni(II) determination. Some important parameters, such as kind and volume of extraction and dispersive solvents, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor for the presented method is 138. The calibration curve was linear over a nickel concentration range of 10-50 ng mL(-1). The detection limit and relative standard deviation were 0.04 ng mL(-1) and 2.1%, respectively. The method was successfully applied to the extraction and determination of Ni(II) in different water samples.