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Öğe Investigating sorption characteristics of copper ions onto insolubilized humic acid by using a continuously monitored solid phase extraction technique(ELSEVIER SCIENCE BV, 2007) Gezici, Orhan; Kara, Huseyin; Yanik, Sema; Ayyildiz, H. Filiz; Kucukkolbasi, SemahatThe sorption characteristics of Cu(II) in an insolubilized humic acid (IHA) mediated column system were investigated at various experimental conditions using a solid phase extraction (SPE) technique. Sodium form of the IHA (INaA) was used as solid phase and sorption behaviors were evaluated by using common adsorption isotherms as well as Scatchard plot analysis. Regeneration, loading, washing and stripping steps of SPE were carried out consecutively, and their progresses were monitored through breakthrough curves obtained from a continuous flow-through cell adapted UV-vis spectrophotometer. So, the breakthrough curves were used to visualize distribution of Cu(II) concentration between mobile phase and solid phase, and amount of the Cu(II) sorbed by INaA was obtained from AAS analysis of effluents collected during the stripping steps of particular run. Thus, from the obtained results, the sorption characteristics and usability of IHA as a solid phase for SPE of metal ions was evaluated in detail. (c) 2007 Elsevier B.V. All rights reserved.Öğe Sorption behavior of Cu(II) ions on insolubilized humic acid under acidic conditions: An application of Scatchard plot analysis in evaluating the pH dependence of specific and nonspecific bindings(ELSEVIER SCIENCE BV, 2007) Gezici, Orhan; Kara, Huseyin; Ayar, Ahmet; Topkafa, MustafaSorption behavior of Cu(II) ions on a humic acid-based solid phase, insolubilized humic acid (IHA), were investigated under continuous column conditions. The quantitative data were derived on the basis of breakthrough curves obtained at different experimental conditions. For the studied experimental conditions, the highest and lowest observable capacities of IHA toward Cu(II) were found as 48.34 and 0.84 mu mol g(-1), respectively. In order to evaluate the pH dependence of Cu(II) binding on IHA, the effect of influent concentration was investigated at three different pH values (1.0, 2.0 and 3.0), and adsorption isotherms were derived for each acidic condition. The characteristics of Cu(II) bindings were evaluated by using Scatchard plot analysis, and it was observed that under strongly acidic condition, pH 1.0, nonspecific and/or multi-type interactions between Cu(II) and MA were the prevailing effects causing the Cu(II) sorption. On the other hand, at pH 2.0 and 3.0, the role of specific interactions was more clearly observed, and so at pH(s) 2.0 and 3.0, the binding of Cu(II) on IHA was mainly attributed to specific interactions rather than nonspecific ones. For pH 2.0 and 3.0, the binding types of Cu(II) on IHA were sub-classified according to different affinities observed between Cu(II) and IHA, and thus two main types of specific bindings were proposed for the studied influent concentration range (1.0 x 10(-3) to 1.0 X 10(-1) mol l(-1)): Type-1, high-affinity/low capacity and Type-2, low-affinity/high capacity bindings. Finally, probable benefit of each specific binding type in separation of Cu(II) from acidic aqueous media has been discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.Öğe Towards multimodal HPLC separations on humic acid-bonded aminopropyl silica: RPLC and HILIC behavior(ELSEVIER SCIENCE BV, 2011) Gezici, Orhan; Kara, HuseyinThe stationary phase characteristics of the material obtained through immobilization of humic acid (HA) to aminopropyl silica (APS) via amide-bond formation were investigated. The material was characterized in terms of elemental analysis, FTIR, thermogravimetric analyses, pH point of zero charge measurements, potentiometric titrations, and contact angle measurements. Amount of HA bonded to APS was determined from the elemental analysis results, and found as 170 mgHA/gAPS. Stability of the material was studied in aqueous media at different pH values, and amount of HA released at pH = 8 did not exceed 2% of the total immobilized HA. Stationary phase characteristics of the well-characterized material were investigated in an HPLC system by using some low-molecular weight polar compounds (i.e. some nucleosides and nucleobases) as test solutes. Effect of some experimental variables such as column conditioning, composition of mobile phase, and temperature on the chromatographic behavior of the studied compounds was studied. Role of ammonium solutions at different pH values on retentive properties of the species was also studied. Retention factors (k') versus volume percentage of organic modifier exhibited a U-curve, which was evaluated as an indication for RPLC/HILIC mixed-mode behavior of the stationary phase. Orthogonality between RPLC and HILIC modes was analyzed through geometric approach, and found as 48.5%. Base-line separation for the studied groups of compounds was achieved under each studied mode, and some differentiations were observed in elution order of the compounds depending on the HPLC mode applied. Chromatograms recorded under RPLC and HILIC modes were compared with those recorded on APS under similar conditions, and thus the influence/importance of HA immobilization process was evaluated in detail. In light of the obtained results, immobilized HA is represented as a useful stationary phase for HPLC separations. (C) 2011 Elsevier B.V. All rights reserved.Öğe Towards multimodal HPLC separations on humic acid-bonded aminopropyl silica: RPLC and LEC behavior(ELSEVIER SCIENCE BV, 2011) Gezici, Orhan; Kara, HuseyinIn the present study, metal binding property of humic acid (HA) was successfully adapted to the ligand-exchange concept, and metal-loaded immobilized humic acid was used as a ligand exchanger stationary phase for separation of some nucleosides. Humic-acid bonded aminopropyl silica (EC-HA-APS) was turned into ligand exchanger forms by loading aqueous solutions of Cu(2+), and Co(2+) to the column (4.6 X 150; as mm) packed with EC-HA-APS. Metal ion solutions were loaded to the column in a step-wise manner where the concentration of metal ion solution being loaded to the column was increased gradually between 5 and 100 mM. The progress of metal loading process was monitored via the breakthrough curves propagated stepwise. Ligand-exchange chromatography (LEC) studies were performed on an HPLC system, and chromatographic behaviors of the studied nucleosides (i.e. uridine, Urd; thymidine, Tyd; cytidine, Cyd; adenosine, Ado; and guanosine, Guo) were investigated on Cu(2+) and Co(2+) loaded forms of the EC-HA-APS (Cu-EC-HA-APS and Co-EC-HA-APS). Effect of mobile phase composition, temperature, and the type of metal ion loaded to the column on the retentive behaviors of the compounds was studied, in detail. The studied solutes exhibited mixed-mode RPLC/LEC behavior on the stationary phase. Metal-loaded column (M-EC-HA-APS) was easily regenerated into its original form. EC-HA-APS, with 98 +/- 2% metal recoveries, by using aqueous mixture of EDTA + NH(3) at pH = 7.5. Thus, the stationary phase exhibited a high flexibility between RPLC and LEC modes. This property, also, made it possible to convert the stationary phase into various ligand exchanger forms by loading different metal ions. Hence, capacity and selectivity of the stationary phase towards the studied species was manipulated easily by loading different metal ions to the stationary phase. Baseline separation for the studied species was achieved on Cu-EC-HA-APS and Co-EC-HA-APS and some differentiations were observed in capacity and selectivity, depending on the type of metal loaded. Thus, being as the first endeavor on usability of immobilized HA as a ligand exchanger stationary phase, the present study is believed to be useful to understand multifunctional character of HA-based solid/stationary phases. (C) 2011 Elsevier B.V. All rights reserved.
