Browsing by Author "Dost, K"

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    Analysis of artemisinin by a packed-column supercritical fluid chromatography-atmospheric pressure chemical ionisation mass spectrometry technique
    Dost, K; Davidson, G
    A packed-column supercritical fluid chromatography-atmospheric pressure chemical ionisation mass spectrometry method was studied for the determination of artemisinin from Artemisia annua L. extracts. The technique does not require any kind of derivatisation prior to the analysis. All samples were simply dissolved in methanol and injected into the mobile phase. Detection was achieved by using mass spectrometry with atmospheric pressure chemical ionisation. The ionisation technique is relatively soft and provides protonated molecular ion and informative structural fragmentation for the compound. Benzophenone was used as a chromatographic standard for the determination of the analytical reproducibility. The supercritical carbon dioxide mobile phase used in the system was modified by 10% methanol. The average absolute retention time was 3.54 min with a standard deviation of 0.017 min and a relative standard deviation of 0.4% with respect to benzophenone for the procedure. The correlation coefficient was 0.998 and detection limit 370 pg on column.
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    Investigation of Phenolic Content in Five Different Pine Barks Species Grown in Turkey by HPLC-UV and LC-MS
    Seker, ME; Çelik, A; Dost, K; Erdogan, A
    Investigation of phenolic content from different pine bark species grown in Turkey was performed using a reversed-phase high pressure liquid chromatography with ultraviolet (RP-HPLC-UV) method. All phenolic constituents were separated in <26 min on reversed-phase C18 column with gradient mobile phase that consists of orthophosphoric acid, methanol and acetonitrile. Detections were made on an UV detector at 280 nm and at a flow rate of 1 mL/min. Samples were prepared according to Masqueller's conventional sample preparation method with slight modifications. To avoid the reduction in extraction efficiency the sample preparation step was carried out under argon atmosphere. The linearity of the method was between 0.9994 and 0.9999. The detection limits for the five phenolic constituents ranged from 0122 to 0.324 mg/L. Catechin and taxifolin were found in all pine barks at a concentration of 0.065 +/- 0.002-1.454 +/- 0.004 and 0.015 +/- 0.001-23.164 +/- 0.322 mg/g, respectively. Epicatechin was determined in four pine barks between 0.027 +/- 0.001 and 0.076 +/- 0.002 mg/g, ferulic acid in two pine barks between 0.010 +/- 0.001 and 0.022 +/- 0.001 mg/g and epicatechin gallate in only one of the pine barks at 0.025 +/- 0.001 mg/g. Finally, the total amount of phenolic compounds and antioxidant capacities of the pine barks were found to be very high.
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    Evaluation of Phytic Acid Content of Some Tea and Nut Products by Reverse-Phase High Performance Liquid Chromatography/Visible Detector
    Dost, K; Karaca, G
    Phytic acid contents of nine different types of nut and six different types of tea and steeped tea were analysed by reverse-phase high performance liquid chromatography with visible detector. The extraction method was based on hydrochloric acid extraction, and the analysis method was based on metal replacement reaction of phytic acid from coloured complex (iron(III)-thiocyanate), separation on CN column and monitoring the absorbance at 460 nm. The retention time for the monitored iron(III)-thiocyanate peak was achieved less than 3 min. The proposed HPLC/Vis procedure shows good linearity over the concentration range of 1-150 mg L-1 with a correlation coefficient value of 0.9938. The effectiveness of metal replacement reaction was presented in terms of relative standard deviation that was 0.62 and 0.88 % for 5 and 50 mg L-1 of phytic acid, respectively. Repeatability of the analytical method was ranging between 1.58-7.88 % (n = 10, for 50 mg L-1) and 0.98-4.63 % (n = 10, for 5 mg L-1) in terms of relative standard deviation. Accuracy of the method is good, ranging relative error between 4.52 and 8.00 % (n = 10, for 50 mg L-1). Phytic acid content is in the range of 1.54 to 9.74 mg g(-1) in nuts, 27.67 to 28.82 mg g(-1) in green teas, and 20.49 to 21.96 mg g(-1) in pocketed roasted teas.
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    Determination of polycyclic aromatic hydrocarbons in edible oils and barbecued food by HPLC/UV-Vis detection
    Dost, K; Ideli, C
    Determination of nine polycyclic aromatic hydrocarbons in corn, sunflower, olive oils and barbecued meat and fish by HPLC/UV-Vis method is described. The extraction procedure included a saponification, liquid-liquid extraction and finally purification of PAHs through a house-made silica-alumina column. Chromatographic determination was based on separation of PAHs on ODS column and measurement at 254 nm. All polycyclic aromatic hydrocarbons were separated and analyzed in 12 min on reversed phase ODS column with acetonitrile/water mobile phase at 1.5 mL min(-1) flow rate. The detection limits of nine polycyclic aromatic hydrocarbons ranged from 0.26 to 1.15 mu g L-1 at a signal/noise ratio of 3. The linearity of the method was between 0.9951 and 0.9996. Oil samples contain different PAHs ranging from 0.44 to 98.92 mu g L-1. Barbecuing process increased the concentration (in the range of 2- to 8-fold) and caused the formation of PAHs in food samples. (C) 2012 Elsevier Ltd. All rights reserved.
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    Determination of phytic acid in wheat and wheat products by reverse phase high performance liquid chromatography
    Dost, K; Tokul, O
    A sensitive method for accurate determination of phytic acid in food samples is described. The proposed procedure involves high performance liquid chromatography (HPLC) and UV-vis detection. The method was based on metal replacement reaction of phytic acid from coloured complex (iron(M)-thiocyanate), separation and monitoring any decrease in concentration of coloured complex. The retention time for the monitored iron(III)-thiocyanate peak was achieved in less then 3 min in Gaussian shape. The proposed HPLC/UV-vis procedure shows good linearity over the concentration range of 10-125 mu g ml(-1) with correlation coefficient value of 0.997. The procedure is reproducible and accurate, illustrating a standard deviation between 0.72 and 1.20 mu g ml(-1) (n = 10, for 50 mu g ml(-1)) and relative standard deviation between 1.40 and 2.98% (n = 10, for 50 mu g ml(-1)) within and between days for reproducibility and absolute error ranging between 0.16 and 1.54% (n = 10, for 100 mu g ml(-1)) within and between days for accuracy, respectively. Detection limit was estimated as 0.5 mu g ml(-1) which is suitable for analysis of foodstuffs and plant materials in that phytic acid usually presents within 2.5-50 mu g ml(-1) range. The procedure was then applied to determination of phytic acid in wheat and wheat products. The content of the phytic acid in the samples was calculated by using the calibration curve obtained from the standard solution of phytic acid and iron(IH)-thiocyanate solutions containing 100 mu g ml(-1) iron(RI) ion. (c) 2005 Published by Elsevier B.V.
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    Arsenic removal from aqueous system using natural and modified (Kula ebonite and zeolite) adsorbents
    Gülbas, G; Tirtom, VN; Çelik, A; Dost, K
    Natural adsorbents (Kula ebonite, zeolite and zeolite treated with Al2(SO4)3; Al2(SO4)3+NaOH; FeCl3 and FeCl3+NaOH) were prepared and employed by means of batch method for selective adsorption and removal of arsenic from aqueous system. The influences of different parameters such as, contact time, pH, temperature, and concentration of adsorbate on adsorption performance of zeolite and zeolite treated with FeCl3 and FeCl3+NaOH were studied in order to optimize the adsorption conditions. Batch adsorption studies have shown that removal capacity of zeolite from aqueous solutions can be increased by FeCl3 and FeCl3+NaOH treatment. The maximum adsorption capacities were 1.99 and 3.43 mg g-1 of zeolite which was treated with FeCl3 and FeCl3+NaOH for arsenic, respectively. The adsorption data obtained follows a first-order rate expression and fits the Langmuir isotherm that has been used to obtain thethermodynamic parameters. In addition, the thermodynamic parameters, standard free energy (?G degrees), standard enthalpy (?H degrees), standard entropy (?S degrees) of the adsorption process were calculated. It was found that the adsorption of arsenic on zeolite was exothermic. (c) 2011 American Institute of Chemical Engineers Environ Prog, 2011
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    Determination of oleuropein using multiwalled carbon nanotube modified glassy carbon electrode by adsorptive stripping square wave voltammetry
    Cittan, M; Koçak, S; Çelik, A; Dost, K
    A multi-walled carbon nanotube modified glassy carbon electrode was used to prepare an electrochemical sensing platform for the determination of oleuropein. Results showed that, the accumulation of oleuropein on the prepared electrode takes place with the adsorption process. Electrochemical behavior of oleuropein was studied by using cyclic voltammetry. Compared to the bare GCE, the oxidation peak current of oleuropein increased about 340 times at MWCNT/GCE. Voltammetric determination of oleuropein on the surface of prepared electrode was studied using square wave voltammetry where the oxidation peak current of oleuropein was measured as an analytical signal. A calibration curve of oleuropein was performed between 0.01 and 0.70 mu M and a good linearity was obtained with a correlation coefficient of 0.9984. Detection and quantification limits of the method were obtained as 2.73 and 9.09 nM, respectively. In addition, intra-day and inter-day precision studies indicated that the voltammetric method was sufficiently repeatable. Finally, the proposed electrochemical sensor was successfully applied to the determination of oleuropein in an olive leaf extract. Microwave-assisted extraction of oleuropein had good recovery values between 92% and 98%. The results obtained with the proposed electrochemical sensor were compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. (C) 2016 Elsevier B.V. All rights reserved.
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    Simultaneous Electrochemical Determination of Sildenafil Citrate and Tadalafil Using a Multi Walled Carbon Nanotubes Modified Glassy Carbon Electrode by Adsorptive Stripping Linear Sweep Voltammetry
    Öksüz, M; Cittan, M; Dost, K
    An adsorptive stripping linear sweep voltammetric method was developed for the simultaneous determination of sildenafil citrate and tadalafil. The voltammetric working electrode was a glassy carbon electrode modified with carboxylic multi-walled carbon nanotubes. The sensitivity of the developed voltammetric method was significantly increased by this modification. Both analytes spontaneously adsorbed on the modified electrode surface due to their adsorption affinities. The irreversible oxidation signals of both analytes were used as the analytical signals. The electrochemical behaviour of sildenafil citrate and tadalafil was assessed using cyclic voltammetry. The developed voltammetric method was linear in the range of 0.01-0.50 mu M with a correlation coefficient of 0.9997 and 0.9985 for sildenafil citrate and tadalafil, respectively. The LOQs of the method for both analytes were 0.010 mu M. The intra- and inter-day reproducibility of the method was less than 10% RSD in all cases. The extraction recoveries for both analytes ranged between 83 and 94%. The applicability of the developed voltammetric method were investigated by determining the analyte in two different spiked samples (an energy drink and a traditional herbal product). Furthermore, the described method would represent the first electrochemical approach for the simultaneous detection of sildenafil citrate and tadalafil, providing an available alternative to current chromatographic techniques.
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    An investigation of chromium(VI) ion removal from wastewaters by adsorption on residual lignin
    Celik, A; Dost, K; Sezer, H
    The aim of this study was to develop a low-cost method for effective removal of Cr(VI) ions from wastewater, but also to valuate this residual of major industry for its adsorption capacity. Therefore, the residual lignin produced from paper industry was utilised as an adsorption material and the effects of lignin amount used, pH of solution and contact time on removal capacity of chromium from wastewater were investigated. Analysis of Cr(VI) ions was performed with both spectrometric and volumetric standard methods. The results obtained from both methods were in good agreement with 2% relative error. Ninety-three % of Cr(VI) ions were adsorbed by 0.5 g residual lignin at pH 3 and 7 hours contact time. This result underlines that residual lignin could be used as a low-cost adsorbent material to remove Cr(VI) ions discharged into the environment with wastewaters.
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    Simultaneous determination of six antibiotics belonging to four different classes in chicken meat BY HPLC/DAD and verification BY LC-MS/MS
    Doyuk, F; Dost, K
    The hypothesis of this study was to develop an extraction method allowing side-by-side extraction of six antibiotics belonging to four different classes and an HPLC/DAD method for the determination of their residues in chicken breast meat. The validation data showed that this hypothesis was achieved. The results were then confirmed by LC-MS/MS method. Sample preparation was based on the classical solid-liquid extraction with methanolic citric acid. The average recoveries were satisfactory and ranged from 75.68 to 101.3%. The linearity of the developed HPLC/DAD method was very high in the concentration range studied (R-2 > 0.9969). The accuracy and precision of the analytical method were between -10.8 and 12.0% relative error and 0.82 to 10.1% relative standard deviation, respectively. The LODs for five antibiotics ranged from 0.6 to 2.7 mu g kg(-1) and LOQs ranged from 2.0 to 8.9 mu g kg(-1). For penicillin G, the LOD was 0.16 and LOQ was 0.52 mg k(g-1).
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    Determination of boscalid, pyraclostrobin and trifloxystrobin in dried grape and apricot by HPLC/UV method
    Dost, K; Öksüz, M; Cittan, M; Mutlu, B; Tural, B
    This paper describes the development of extraction and high-performance liquid chromatography with ultraviolet detection methods for the determination of boscalid, pyraclostrobin, and trifloxystrobin. The extraction method includes classical solid-liquid and liquid-liquid extraction methods. The fungicides and the internal standard were separated in less than 6.5 min on an ODS column with acetonitrile/water mobile phase at 1.5 mL min- 1 flow rate and detected at 265 nm. The limit of detection and quantification were 0.0084 and 0.0280 mg kg-1 for boscalid; 0.0032 and 0.0106 mg kg- 1 for pyraclostrobin; 0.0113 and 0.0377 mg kg- 1 for trifloxystrobin. The reproducibility of the method was lower than 0.6 % and 0.7 % relative standard deviation in terms of retention time for within day and between days, respectively, lower than 1.4 % in terms of the ratio of peak areas for both within day and between days. The accuracy of the analysis method in terms of relative error was lower than 11 % at low, 8 % at medium and 1 % at high concentrations. The recoveries were between 99-106 % for boscalid, 70-82 % for pyraclostrobin and 52-64 % for trifloxystrobin. These developed methods were then applied for the determination of selected fungicides in dried grape and apricot samples.
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