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    HPLC Separation of Different Groups of Small Polar Compounds on a Novel Amide-Embedded Stationary Phase
    (Springer Heidelberg, 2014) Aral, Hayriye; Aral, Tarik; Celik, K. Serdar; Ziyadanogullari, Berrin; Ziyadanogullari, Recep
    Retention behaviors of an amide-embedded silica base stationary phase, which was recently developed by our group, were studied by using six different groups of small polar compounds including phenolic compounds, substituted anilines, chlorinated herbicides, Sudan dyes and some nucleotides and nucleosides in HPLC. The chromatographic behaviors of the prepared stationary phase for these analytes were compared with those of a commercially available reversed-phase column ACE C18 under same conditions. Among the six groups of analytes studied, the amide-silica stationary phase showed enhanced selectivity towards phenolic compounds, substituted anilines, Sudan dyes and herbicides under reversed-phase conditions and satisfactory selectivity towards nucleosides and nucleotides which could not be separated with ACE C18 column under HILIC conditions. Experimental data provided some evidence that functional groups on the stationary phases might have certain degrees of influence on selectivity possibly through secondary interactions with the model compounds. The retentions of the moderately polar compounds such as phenolic acids, anilines and herbicides on the stationary phase are higher than highly polar compounds such as nucleotides and nucleosides due to both the hydrophobic and hydrophilic interactions between the stationary phase and analytes. The quantitative determination of Sudan dyes (I, II, III, and IV) in red chilli peppers was performed. Many red chilli peppers were screened and three of them contained Sudans dyes.
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    ICP-OES Multi-element Analysis of Wheat Grown in Southeastern Turkey
    (Atomic Spectroscopy Press Ltd, 2017) Duz, M. Zahir; Duzgun, Mehmet; Cam, Belgizar; Celik, K. Serdar; Kilinc, Ersin
    The bread and durum wheat varieties grown in Southeastern Turkey are the main source of food consumed by the Turkish population and serve as bread and pasta. In this study, 12 kinds of durum wheat and 5 kinds of bread wheat samples registered by the International Agricultural Research and Training Centre of Turkey (IARTC, Turkey) were investigated for their multi-elemental concentrations (Ca, K, Mg, Fe, Zn, Mn, Si, Sn, Cu, Cr, Cd, Ni, V, Pb, As, and Se). The samples were microwave digested and the elements determined by ICP-OES. The results were in good agreement with the certified values. This study shows that the elements Si, Fe, Zn, Cd, Cr, Cu, Sn, and Pb in durum wheat were higher than in bread wheat. Both wheat species were found to be rich in terms of Ca, Mg, and K. The multi-element content of some bread wheat and durum wheat was also in good agreement with the maximum allowable levels of the Food and Agriculture Organization (FAO) World Health (WHO).
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    Microwave Digestion Followed by ICP-OES for the Determination of Al, Cd, Cr, Cu, Fe, Ni, Pb, and Sn in Maize
    (Atomic Spectroscopy Press Ltd, 2012) Duz, M. Zahir; Celik, K. Serdar; Aydin, Isil; Erdogan, Sait; Aydin, Firat; Hamamci, Candan
    Maize (Zea mays L.) is currently the most widely grown crop in the world and is used not only for food and animal feed but also to produce industrial starches, biodiesel, ethanol, and oils. The present work reports the results obtained by the proposed method for the determination of metals (M, Cd, Cr, Cu, Fe, Ni, Pb and Sn) in maize by ICP-OES, using digestion with an oxidant mixture in a closed-vessel microwave oven. The results in the maize samples (minimum-maximum in mg/kg) were: Al 6.678-7.051, Sn 2.092-3.977, Cr 0.394-0.423, Cu 21.56-24.78, Fe 93.37-102.86, Ni 1.679-1.877 and Pb 0.375-0.392. The concentration of Cd was below the detection limit (< 0.03 mg/kg). The certified reference material, CRM NIST1573a Tomato Leaves, was used in order to verify the accuracy of the microwave digestion method. The results of this study were in good agreement with the certified values.
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    Preparation of a novel ionic hybrid stationary phase by non-covalent functionalization of single-walled carbon nanotubes with amino-derivatized silica gel for fast HPLC separation of aromatic compounds
    (Elsevier Science Bv, 2016) Aral, Hayriye; Celik, K. Serdar; Aral, Tarik; Topal, Giray
    Single-walled carbon nanotubes (SWCNTs) were immobilized on spherical silica gel with a 4-mu m average particle size and a 60-angstrom average pore size. The amino-derivatized silica gel was non-covalently coated with carboxylated SWCNTs to preserve the structure of the nanotubes and their physico-chemical properties. The novel ionic hybrid stationary phase was characterized by scanning electron microscopy (SEM), infra-red (IR) spectroscopy and elemental analysis, and then, it was used to fill an empty 150 x 4.6 mm(2) high-performance liquid chromatography (HPLC) column. Chromatographic parameters, such as the theoretical plate number, retention factor and peak asymmetry factor, and analytical parameters, such as the limit of detection (LOD), limit of quantification (LOQ), linear range, calibration equation, and R-2 value, and quantitative analysis parameters were calculated for all of the analytes. Using different mobile phases, five different classes of aromatic hydrocarbons were separated in a very short analysis time of 4-8 min. Furthermore, a high theoretical plate number (up to 25000) and an excellent peak asymmetry factor (1.0) were obtained. The results showed that the surface of the SWNTs had very strong interactions with aromatic groups, therefore providing high selectivity for the separation of different classes of aromatic compounds. This study indicates that SWCNTs enable the extension of the application range of the newly prepared stationary phases for the fast separation of aromatic compounds by HPLC. (C) 2015 Elsevier B.V. All rights reserved.
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    Simultaneous Determination of Transition Metals in Hazelnuts (Corylus avellana L.) by ICP-OES
    (Atomic Spectroscopy Press Ltd, 2014) Celik, K. Serdar; Aydin, Firat; Duz, M. Zahir; Aydin, Isil; Erdogan, Sait; Akba, Osman; Hamamci, Candan
    Heavy metal concentrations in foods are of interest because of their essential or toxic nature. The present work reports the results obtained for the simultaneous determination of essential and/or toxic metals (Cd, Co, Cr, Cu, Fe, Ni, Pb, Zn) in 24 hazelnut samples by inductively coupled plasma optical emission spectrometry (ICP-OES) after sample digestion using a diluted oxidant mixture in a closed-vessel microwave system. The obtained results (mean in mg/kg) were: Co 1.15, Cr 1.92, Cu 17.96, Fe 489, Ni 4.76, and Zn 85. The concentrations of Cd and Pb were below the detection limits and are below the daily intake recommended by the international organizations (WHO). Therefore, it can be stated that hazelnuts are safe for public consumption. The macro and micro nutrient ranges in hazelnut (Corylus avellana L.) did not exceed the dietary reference intake (DRI).
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    Simultaneous Multielement Determination of Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sn, and Zn in Bulgur Wheat by ICP-OES
    (Atomic Spectroscopy Press Ltd, 2015) Erdogan, Sait; Aydin, Isil; Duz, M. Zahir; Aydin, Firat; Celik, K. Serdar; Akba, Osman; Hamamci, Candan
    Bulgur is one of the oldest cereal-based foods. This study explains the simultaneous determination by the proposed method for toxic elements such as Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sn, and Zn in bulgur by ICP-OES following digestion in a closed-vessel microwave system. The ICP-OES method is used because it is precise, rapid, simple, and accurate for the determination of 12 metals. The technique can be considered useful for the routine analysis of multi-elements in cereals as well as for quality control purposes. The obtained results in the bulgur samples (mean in mg kg(-1)) were: Al 0.81, Cr 0.19, Cu 3.80, Fe 26.75, Mn 13.60, Ni 0.25, Pb 0.23, Sn 0.17, and Zn 14.30. The concentrations of As, Cd, and Hg were below the detection limits. A certified reference material was used to verify the accuracy of the studied method. The results were in good agreement with the certified values. The toxic metal concentrations are low and the obtained values are suitable for daily intake. The macro and micro nutrient ranges in bulgar wheat did not exceed the dietary reference intake (DRI). The bulgur produced in Turkey has very low levels of toxic metals, is safe for human consumption, and is a highly nutritional and healthy food source. Bulgur wheat is, therefore, safe for public consumption.