Ahmet E. Eroğlu

Sorption Efficiency of Chitosan Nanofibers toward Metal Ions at Low Concentrations

Chitosan fibers showing narrow diameter distribution with a mean of 42 nm were produced by electrospinning and utilized for the sorption of Fe(III), Cu(II), Ag(I), and Cd(II) ions from aqueous solutions. The ion concentrations in the supernatant solutions were determined using inductively coupled plasma-mass spectrometry (ICP-MS). The filtration efficiency of the fibers toward these ions was studied by both batch and microcolumn methods. High efficiency in sorption of the metal ions was obtained in the both methods. The effects of sorbent amount (0.10-0.50 mg), shaking time (15-120 min), initial metal ion concentration (10.0-1000.0 μg·L(-1)), and temperature (25 and 50 °C) on the extent of sorption were examined. The sorbent amount did not significantly alter the efficiency of sorption; however, shaking time, temperature, and metal ion concentration were found to have a strong influence on sorption. By virtue of its mechanical integrity, the applicability of the chitosan mat in solid phase extraction under continuous flow looks promising.

Determination of technetium in sea-water using ion exchange and inductively coupled plasma mass spectrometry with ultrasonic nebulisation

An enrichment–separation scheme employing a strong-base type anion-exchange resin was developed for the determination of99Tc in sea-water by inductively coupled plasma mass spectrometry utilising ultrasonic nebulisation with membrane desolvation. Samples were processed through an anion-exchange column to enrich Tc and to eliminate sea-water matrix ions. The limit of detection for 99Tc in sea-water based on processing a 14 ml sample was 0.03 ng l–1. Accuracy was verified with spike recovery experiments. The potential for rapid on-line sample processing via a microcolumn–flow injection system was demonstrated.

Biosorption of Cu(II) and Pb(II) ions from aqueous solution by natural spider silk

Aside from its excellent mechanical properties, spider silk (SS) would offer an active surface for heavy metal interaction due to its rich protein structure. The present study describes the potential use of natural (SS) as a sorbent of heavy metals from aqueous solutions. Single and multi-species biosorption experiments of heavy metals by natural SS were conducted using batch and column experiments. The biosorption kinetics, in general, was found to follow the second-order rate expression, and the experimental equilibrium biosorption data fitted reasonably well to Freundlich isotherm. From the Freundlich isotherm, the biosorption capacities of Cu(II) and Pb(II) ions onto SS were found as 0.20 and 0.007 mmol g⁻¹, respectively. The results showed a decrease in the extent of metal ion uptake with lowering the pH.

Speciation and preconcentration of inorganic antimony in waters by Duolite GT-73 microcolumn and determination by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS).

A selective matrix removal/separation/enrichment method, utilizing a microcolumn of a chelating resin with SH functional groups (Duolite GT-73), was proposed for the determination of Sb(III) in waters by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS). The resin was selective to Sb(III) at almost all pH and acidity values employed, whereas Sb(V) was not retained at all and could be determined after a pre-reduction step with l-cysteine. Spike recoveries were tested at various concentration levels in different water types and were found to vary between 85 and 118%. Accuracy of the proposed methodology was checked by analyzing a standard reference material and a good correlation was found between the determined (13.3+/-1.1mugl(-1)) and the certified value (13.79+/-0.42mugl(-1)). The method was applied to several bottled drinking water samples for antimony determination with and without preconcentration and none of the samples were found to contain antimony above the permissible level (5mugl(-1)). The characteristic concentration (the concentration of the analyte corresponding to an absorbance of 0.0044) was 0.55mugl(-1) and the 3s limit of detection (LOD) based on five times preconcentration was 0.06mugl(-1). The applicability of the microcolumn separation/preconcentration/matrix removal method for flow injection systems was also demonstrated.

Sorption of As(V) from waters using chitosan and chitosan-immobilized sodium silicate prior to atomic spectrometric determination

A natural biosorbent containing amine functional groups, chitosan, and a novel sorbent, chitosan-immobilized sodium silicate, were prepared and utilized for the selective sorption of As(V) from waters prior to its determination by atomic spectrometric techniques, namely, hydride generation atomic absorption spectrometry (HGAAS) and inductively coupled plasma mass spectrometry (ICP-MS). Chitosan was synthesized from chitin and sodium silicate was used as the immobilization matrix due to its straightforward synthesis. Through sequential sorption studies, it was shown that chitosan-immobilized sodium silicate has exhibited a better chemical stability than the chitosan itself which demonstrates the advantage of immobilization method. Both chitosan and chitosan-immobilized sodium silicate were shown to selectively adsorb As(V), arsenate, from waters at pH 3.0 at which neither chitin nor sodium silicate displayed any sorption towards As(V). The sorption of arsenate by chitosan is supposed to have electrostatic nature since pH of 3.0 is both the point at which the amino groups in chitosan are protonated and also the predominant form of As(V) is H(2)AsO(4)(-). A pre-oxidation step is required if both As(III) and As(V) are to be determined. Desorption from the sorbents was realized with 1.0% (w/v) l-cysteine prepared in a pH 3.0 solution adjusted with HCl. Among the possible interfering species tested, only Te(IV) and Sb(III) were shown to cause a decrease in the sorption capacity especially at high interferant concentrations. High concentrations of Sb(III) also resulted in gas phase interference during hydride generation. The validity of the method was checked both via spike recovery experiments and also through the analysis of a standard reference material. Spike recovery tests were carried out with four different types of water; namely, ultra-pure, bottled drinking, tap, and sea water; and percent recovery values were found to be 114 (+/-4), 112 (+/-2), 43 (+/-4), and 0 (+/-1), respectively. It was concluded that the proposed methodology can be applied efficiently to low-to-medium ionic strength solutions, such as most drinking waters. The accuracy of the method was additionally investigated through the analysis of a standard reference material and a good correlation was found between the determined (26.6+/-2.4microgL(-1)) and the certified (26.67microgL(-1)) value.

Kinetic and thermodynamic investigations of strontium ions retention by natural kaolinite and clinoptilolite minerals

Summary The current study was devoted to the determination of various thermodynamic and kinetic parameters resulting from the fixation of Sr2+ by natural samples of kaolinite and clinoptilolite minerals. The sorption process followed pseudo second order kinetics, with faster sorption on kaolinite compared to clinoptilolite, where the uptake is affected by intraparticle diffusion. Freundlich and Dubinin–Radushkevich isotherm models described the data more adequately than Langmuir model, and clinoptilolite showed a higher strontium sorption capacity than kaolinite. Thermodynamically, the activation energy of Sr2+ sorption by kaolinite and clinoptilolite were respectively, −8.5 and −18.4 kJ/mol. The sorption process on both minerals was spontaneous and endothermic at all the studied concentrations, with ΔH° being 11.3 and 9.8 kJ/mol, for sorption on kaolinite and clinoptilolite, respectively. The findings of this study were compared with those of an earlier study on the uptake of Cs+ by the same minerals.

Synthesis, characterization and application of a novel mercapto- and amine-bifunctionalized silica for speciation/sorption of inorganic arsenic prior to inductively coupled plasma mass spectrometric determination.

A bifunctional sorbent, (NH(2)+SH)silica, containing both amine and mercapto functionalities was prepared by modification of silica gel with 3-(triethoxysilyl)propylamine and (3-mercaptopropyl)trimethoxysilane. In addition to the bifunctional sorbent, silica gel was modified individually with the functional mercapto- and amino-silanes, and the mono-functional sorbents, namely (SH)silica and (NH(2))silica, were also mechanically mixed ((NH(2))silica+(SH)silica) for the sake of comparison of sorption performances. It has been demonstrated that (SH)silica shows quantitative sorption only to As(III) at two pH values, 1.0 and 9.0, while (NH(2))silica displays selectivity only towards As(V) at pH 3.0. On the other hand, the bifunctional (NH(2)+SH)silica possesses the efficient features of the two mono-functionalized sorbents; for example, it retains As(III) at a wider pH range, from 1.0 to at least 9.0 with the exception at pH 2.0, and it also shows quantitative sorption to As(V) at pH 3.0. This property gives the bifunctional (NH(2)+SH)silica a better flexibility in terms of sorption performance as a function of solution pH. The mechanically mixed (NH(2))silica+(SH)silica exhibits a similar but less efficient sorption behavior compared to the bifunctional sorbent. Desorption of both As(III) and As(V) species can be realized using 0.5M NaOH. The validity of the proposed method was checked through the analysis of a standard reference material and a good correlation was obtained between the certified (26.67 μg L(-1)) and determined (27.53±0.37 μg L(-1)) values. Spike recovery tests realized with ultrapure water (93.0±2.3%) and drinking water (86.9±1.2%) also confirmed the applicability of the method.

Preparation and characterization of sodium dodecyl sulfate doped polypyrrole solid phase micro extraction fiber and its application to endocrine disruptor pesticide analysis.

A robust in house solid-phase micro extraction (SPME) surface has been developed for the headspace (HS)-SPME determination of endocrine disruptor pesticides, namely, Chlorpyrifos, Penconazole, Procymidone, Bromopropylate and Lambda-Cyhalothrin in wine sample by using sodium dodecylsulfate doped polypyrrole SPME fiber. Pyrrole monomer was electrochemically polymerized on a stainless steel wire in laboratory conditions in virtue of diminishing the cost and enhancing the analyte retention on its surface to exert better selectivity and hence the developed polymerized surface could offer to analyst to exploit it as a fiber in headspace SPME analysis. The parameters, mainly, adsorption temperature and time, desorption temperature, stirring rate and salt amount were optimized to be as 70°C and 45min, 200°C, 600rpm and 10gL(-1), respectively. Limit of detection was estimated in the range of 0.073-1.659ngmL(-1) for the pesticides studied. The developed method was applied in to red wine sample with acceptable recovery values (92-107%) which were obtained for these selected pesticides.

Electrospun amino-functionalized PDMS as a novel SPME sorbent for the speciation of inorganic and organometallic arsenic species

Sol–gel based amine-functionalized SPME fibers (PDMS-weak anion exchanger) were prepared and used for direct mode extraction of dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), and arsenate (As(V)) from aqueous solutions followed by HPLC-ICPMS determination. Two different methods of coating were employed: (i) electrospinning and (ii) dip coating. Electrospinning was used for the first time for preparation of sol–gel based SPME fibers and was found to be superior in terms of extracted amount of arsenicals, coating homogeneity, accessibility of amine groups on the surface, and preparation time for a single fiber. Various parameters such as solution pH, extraction time, agitation speed, extraction temperature, and ionic strength were studied. Optimum extraction conditions were determined as pH of 5.0, extraction time of 30 min, agitation speed of 700 rpm, and extraction temperature of 20 °C. Extraction ability of the novel coating decreased by the addition of NaCl as a consequence of the competition between anionic arsenic species and chloride ions for active sites of the weak anion exchanger. This novel sol–gel coating prepared by electrospinning was found to be promising for SPME applications. Vibrational spectroscopy revealed the alignment of PDMS chains by elongational force under electrospinning process. The chain alignment accordingly orients the pendant amino functional groups perpendicular to the fiber surface, which may develop the free active functional groups available to the medium and lead to the enhancement of the extraction performance. Moreover, the proposed coating strategy through electrospinning might be able to break new ground for various applications in analytical chemistry as well as other disciplines.

Effects of humic acid on root development and nutrient uptake of Vicia faba L. (Broad Bean) seedlings grown under aluminum toxicity

Interactions of humic acid with development and uptake by seedlings of Vicia faba L., (cv. Eresen 87) grown in conditions of aluminium toxicity have been investigated in pot experiments in a controlled greenhouse environment. The objective of the study was to investigate whether humic acid moderates aluminum toxicity. The seedlings were treated with solutions of aluminum chloride (AlCl3) prepared in Hoagland control nutrient solution (HO) and 50 and100 μM and humic acid + Hoagland (HA) solutions, respectively. The 50 and100 μM HA solutions increased root fresh (RFW) and dry (RDW) weights, where the RFW differed significantly from controls (HO) after statistical evaluation by NCSS (NCSS, Kaysville, Utah) with two-sample T-test range at the 5% level. The results of the current experiment suggested that humic acid had suppressed or counteracted the toxic effect of aluminum (Al3+) on both main and lateral root growth. Humic acid seems to block the effect of Al3+ on nutrient uptake, as tested by atomic absorption spectrophotometry (AAS) and flame photometery (FP). Al3+ content in the roots was significantly decreased by 219% in 50-μM HA and by 49% in 100-μM HA treatments respectively. Potassium (K+), sodium (Na+), and iron (Fe3+) were recorded as the other elements taken up in the greatest amounts among the tested nutrients, in addition to Al3+. Humic acid increased the contents of Na+, K+, manganese (Mn2+), and zinc (Zn2+) significantly in both concentrations of HA treatment compared to controls. The Fe3+ content in the roots decreased, in both treatments of HA, application by 252% and 32% respectively. The reduction in the former was significant.