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Dive into the research topics where Erol Erçağ is active.

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Featured researches published by Erol Erçağ.


International Journal of Food Sciences and Nutrition | 2006

The cupric ion reducing antioxidant capacity and polyphenolic content of some herbal teas

Reşat Apak; Kubilay Güçlü; Mustafa Özyürek; Saliha Esin Karademir; Erol Erçağ

The total antioxidant capacity of the aqueous extracts of some endemic herbs—prepared as infusions by steeping these herbs in hot water—was assayed with bis(neocuproine)copper(II) chloride, also known as the cupric ion reducing antioxidant capacity (CUPRAC) reagent, which was easily accessible, rapid, stable and responsive to both hydrophilic and lipophilic antioxidants. The highest antioxidant capacities of some herbal teas available in the Turkish market were observed for scarlet pimpernel (Anagallis arvensis), sweet basil (Ocimum basilicum), green tea (Camellia sinensis) and lemon balm (Melissa officinalis), in this order (1.63, 1.18, 1.07, and 0.99 mmol trolox equivalent (TR)/g, respectively). For infusions prepared from ready-to-use tea bags, the CUPRAC values were highest for Ceylon blended ordinary tea (4.41), green tea with lemon (1.61), English breakfast ordinary tea (1.26) and green tea (0.94), all of which were manufactured types of C. sinensis. Following the strongest antioxidant herbs with capacities close to or slightly exceeding 1.0 mmol TR/g, sage, thyme, coriander, coltsfoot, blackberry and immortelle (Helichrysum) exhibited capacities around 0.5 mmol TR/g. The correlation of the Folin total phenolic content of herbal teas with their CUPRAC and ABTS (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) total antioxidant capacities gave linear curves with correlation coefficients of 0.966 and 0.936, respectively, showing that the CUPRAC assay results better correlated with total phenolic content of herbal teas. Absorbance versus concentration data at different dilutions and upon standard additions of model antioxidant compounds (trolox and quercetin) to herbal tea infusions showed that the absorbances (at 450 nm of the CUPRAC method) due to different antioxidant compounds in herbal tea infusions were additive; that is, the tested antioxidants did not chemically interact to cause apparent deviations from Beers law.


Journal of Chemical Technology & Biotechnology | 1997

Furnace smelting and extractive metallurgy of red mud: Recovery of TiO2, Al2O3 and pig iron

Erol Erçağ; Reşat Apak

Turkish red mud (bauxite waste) has been mixed with dolomite and coke, pelletized and sintered at 1100°C, and finally smelted at 1550°C to produce pig iron and a slag. The slag was leached with 30% H 2 SO 4 at 90°C. The leachate was diluted, ferric iron was reduced with SO 2 , and extracted with 5% D2EHPA solution in kerosene. Silica and Al 2 O 3 were recovered from the remaining aqueous solution, while the organic extract was stripped with 10% Na 2 CO 3 solution, finally hydrolysed and calcined to produce pigment-grade TiO 2 . The titanium recovery efficiency on the basis of slag weight was 84.7%. The extractive separation of titanium from both valencies of iron was investigated as a function of pH and time. A stoichiometric flowsheet for the whole process has been developed.


Talanta | 2009

Selective spectrophotometric determination of TNT using a dicyclohexylamine-based colorimetric sensor.

Erol Erçağ; Ayşem Üzer; Reşat Apak

Because of the extremely heterogeneous distribution of explosives in contaminated soils, on-site colorimetric methods are efficient tools to assess the nature and extent of contamination. To meet the need for rapid and low-cost chemical sensing of explosive traces or residues in soil and post-blast debris, a colorimetric absorption-based sensor for trinitrotoluene (TNT) determination has been developed. The charge-transfer (CT) reagent (dicyclohexylamine, DCHA) is entrapped in a polyvinylchloride (PVC) polymer matrix plasticised with dioctylphtalate (DOP), and moulded into a transparent sensor membrane sliced into test strips capable of sensing TNT showing an absorption maximum at 530 nm when placed in a 1-mm spectrophotometer cell. The sensor gave a linear absorption response to 5-50 mg L(-1) TNT solutions in 30% aqueous acetone with limit of detection (LOD): 3 mg L(-1). The sensor is only affected by tetryl, but not by RDX, pentaerythritoltetranitrate (PETN), dinitrotoluene (DNT), and picric acid. The proposed method was statistically validated for TNT assay against high performance liquid chromatography (HPLC) using a standard sample of Comp B. The developed sensor was relatively resistant to air and water, was of low-cost and high specificity, gave a rapid and reproducible response, and was suitable for field use of TNT determination in both dry and humid soil and groundwater with a portable colorimeter.


Analytical Methods | 2011

A comprehensive review of CUPRAC methodology

Mustafa Özyürek; Kubilay Güçlü; Esma Tütem; Kevser Sözgen Başkan; Erol Erçağ; S. Esin Çelik; Sefa Baki; Leyla Yıldız; Şeyda Karaman; Reşat Apak

Measuring the antioxidant activity/capacity levels of food and biological fluids is carried out for the meaningful comparison of the antioxidant content of foodstuffs and for the diagnosis and treatment of oxidative stress-associated diseases in clinical biochemistry. Current literature clearly states that there is no widely adopted/accepted “total antioxidant parameter” as a nutritional index available for the labeling of food and biological fluids due to the lack of standardized quantitation methods. The “parent” CUPRAC (CUPric Reducing Antioxidant Capacity) method of antioxidant measurement, introduced by our research group to world literature, is based on the absorbance measurement of Cu(I)-neocuproine (Nc) chelate formed as a result of the redox reaction of chain-breaking antioxidants with the CUPRAC reagent, Cu(II)-Nc, where absorbance is recorded at the maximal light absorption wavelength of 450 nm; thus this is an electron-transfer (ET)-based method. From the parent CUPRAC method initially applied to food (apricot, herbal teas, wild edible plants, herby cheese etc.) and biological fluids (as hydrophilic and lipophilic antioxidants together or in separate fractions), a number of “daughter” methods have evolved, such as the simultaneous assay of both lipophilic and hydrophilic antioxidants in acetone-water as methyl-β-cyclodextrin inclusion complexes, determination of ascorbic acid alone in the presence of flavonoids (with preliminary extraction of flavonoids as their La(III)-complexes), determination of hydroxyl radical scavenging activity of both water-soluble antioxidants (using benzoate derivatives and salicylate as hydroxylation probes) and of polyphenols using catalase to stop the Fenton reaction so as to prevent redox cycling of antioxidants, measurement of Cu(II)-catalyzed hydrogen peroxide scavenging activity and of xanthine oxidase inhibition activity of polyphenols, TAC measurement of protein thiols in urea buffer, development of a CUPRAC-based antioxidant sensor on a Nafion cation-exchanger membrane, the off-line HPLC-CUPRAC assay and finally the on-line HPLC-CUPRAC assay of antioxidants with post-column detection. The current direction of CUPRAC methodology can be best described as a self-sufficient and integrated train of measurements providing a useful “antioxidant and antiradical assay package”. This review attempts to unify and summarize various methodologies of main and modified CUPRAC procedures that can normally be extracted from quite different literature sources.


Journal of Environmental Science and Health Part A-toxic\/hazardous Substances & Environmental Engineering | 2002

Kinetic studies on UV-photodegradation of some chlorophenols using TiO2 catalyst.

Mehmet Hugül; Erol Erçağ; Reşat Apak

ABSTRACT A number of chlorophenols, namely 2-chlorophenol, 2,4,-dichlorophenol and 2,4,6-trichlorophenol, were decomposed in aqueous solution by using TiO2 as photoactivated catalyst under UV radiation emitted by a 125 W medium pressure Hg lamp in an immersion well-type quartz photoreactor. The organic-bound chlorine was converted into the environmentally harmless inorganic chloride. For catalyst doses between 0.1 and 0.5 g l−1 the reaction mechanisms are elucidated. The corresponding rate constants were obtained by periodically measuring the remaining chlorophenol, and converted chloride in solution. A theoretical model for the degradation pathway is proposed expressing the rate as a linear function of the concentrations of chlorophenol and catalyst. Aside from the model-calculated values, the pseudo-first order rate constants for a rough approximation of chlorophenols degradation as well as the kinetic parameters of Langmuir-Hinshelwood type decomposition are compared. The photodegradation rate of chlorophenols followed the order: Cl3ċPh>Cl2ċPh>ClċPh.


Analytica Chimica Acta | 2008

Spectrophotometric determination of cyclotrimethylenetrinitramine (RDX) in explosive mixtures and residues with the Berthelot reaction

Ayşem Üzer; Erol Erçağ; Reşat Apak

On-site colorimetric methods are a valuable, cost-effective tool to assess the nature and extent of contamination in remediated sites and to enable on-site screening for police criminology laboratories. The existing colorimetric method for cyclotrimethylenetrinitramine (RDX) based on a Griess reaction suffers from the non-quantitative reduction to nitrite and from the unstable character of HNO2 in acidic medium. Thus we propose a novel spectrophotometric RDX assay in explosive mixtures and residues, based on (Zn+HCl) reduction of RDX in a microwave oven, followed by neutralization of the reduction products to ammonia and low molecular-weight amines, and Berthelot reaction of these amine-compounds with phenol and hypochlorite in alkaline medium to give an intensely blue indophenol dye absorbing at 631nm. The molar absorptivity and limit of detection (LOD) for RDX were (1.08+/-0.04)x10(4) L mol(-1) cm(-1) and 0.18 mg L(-1), respectively. Application of the method to synthetic mixture solutions of RDX and trinitrotoluene (TNT) at varying proportions showed that there was minimal interference from TNT (which could be compensated for by dicyclohexylamine colorimetry), since the Berthelot reaction was essentially non-responsive to m-substituted anilines derived from TNT upon (Zn+HCl) reduction. The proposed method was successfully applied to military-purpose explosive mixtures of (RDX+inert matter) such as Comp A5, Comp C4, and Hexal P30, and to (RDX+TNT) mixtures such as Comp B. The molar absorptivity of RDX was much higher than that of either ammonium or nitrate; RDX could be effectively separated from ammonium and nitrate in soil mixtures, based on solubility differences. The Berthelot method for RDX was statistically validated using Comp B mixtures against standard HPLC equipped with a Hypersil C-18 column with (40% MeOH-60% H2O) mobile phase, and against gas chromatography-thermal energy analysis (GC-TEA) system.


Mikrochimica Acta | 1998

Spectrophotometric determination of gallium(III) with carminic acid and hexadecylpyridinium chloride

Hayati Filik; Esma Tütem; Reşat Apak; Erol Erçağ

The coloured complex formed between Ga(III) and carminic acid (CA) was utilized for developing a spectrophotometric method of gallium determination in the presence of the cationic surfactant hexadecylpyridinium chloride (HDPC), which caused a bathochromic shift in the absorption spectrum and an increase in extinction. The Ga(III)∶: CA molar ratio was 1∶4 in the presence of HDPC. The complex exhibited a molar absorptivity of 3.0 × 104 dm3 mol−1 cm−1 at 570 nm in an aqeous solution of pH 4.O. Beers law was obeyed between 2.0 × 10−6−2.0 × 10−5M Ga(III), and the relative standard deviation for gallium analysis was 1.4%. Most ions did not interfere, with a few exceptions which could be masked with either diethyldithiocarbamate, ascorbic acid, thioglycollic acid or fluoride. The developed method was successfully applied without any preliminary separation to gallium determination in gallium arsenide (GaAs) semiconductor materials, and with prior extraction in a geostandard tonalite sample containing very high proportions of Fe(III) and Al(III).


Analytical Chemistry | 2015

Determination of Triacetone Triperoxide with a N,N-Dimethyl-p-phenylenediamine Sensor on Nafion Using Fe3O4 Magnetic Nanoparticles

Ziya Can; Ayşem Üzer; Kader Türkekul; Erol Erçağ; Reşat Apak

The explosive triacetone triperoxide (TATP) can be easily manufactured from readily accessible reagents and is extremely difficult to detect, owing to the lack of UV absorbance, fluorescence, or facile ionization. The developed method is based on the acidic hydrolysis of TATP into H2O2, pH adjustment to 3.6, and the addition of magnetite nanoparticles (Fe3O4 MNPs) to the medium to produce hydroxyl radicals from H2O2, owing to the peroxidase-like activity of MNPs. The formed radicals converted the N,N-dimethyl-p-phenylenediamine (DMPD) probe to the colored DMPD(+) radical cation, the optical absorbance of which was measured at a wavelength of 554 nm. The molar absorptivity (ε) of the method for TATP was 21.06 × 10(3) L mol(-1) cm(-1). The colored DMPD(+) product in solution could be completely retained on a cation-exchanger Nafion membrane, constituting a colorimetric sensor for TATP and increasing the analytical sensitivity. The proposed method did not respond to a number of hand luggage items like detergent, sweetener, sugar, acetylsalicylic acid (aspirin), and paracetamol-caffeine-based analgesic drugs. On the other hand, TATP could be almost quantitatively recovered from a household detergent and sweetener that can be used as camouflage for the analyte. Neither common soil and groundwater ions (e.g., Ca(2+), Mg(2+), K(+), Cl(-), SO4(2-), and NO3(-)) at 100-fold ratios nor nitro-explosives of trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) at 10-fold amounts interfered with the proposed assay. The method was statistically validated against the standard GC/MS reference method.


Analyst | 2010

Determination of peroxide-based explosives with copper(II)-neocuproine assay combined with a molecular spectroscopic sensor.

Şule Eren; Ayşem Üzer; Ziya Can; Timuçin Kapudan; Erol Erçağ; Reşat Apak

The two members of peroxide-based explosives, triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD), can be manufactured from readily accessible reagents, and are difficult to detect by conventional analytical methods. TATP and HMTD were securely synthesized, taken up with acetone, hydrolyzed with 4 M HCl to hydrogen peroxide, the acidic solution containing H(2)O(2) was neutralized, and assayed by the copper(II)-neocuproine spectrophotometric method. The chromophore of the reaction was the Cu(I)-neocuproine chelate responsible for light absorption at 454 nm. The molar absorptivity (epsilon) of the method for TATP and HMTD was 3.45 x 10(4) and 4.68 x 10(4) L mol(-1) cm(-1), respectively. The TATP recovery from a synthetically contaminated loamy clay soil was 91-99%. The colorimetric method was also applied to a Cu(ii)-neocuproine-impregnated polymeric Nafion membrane sensor developed for the first time in this work for peroxide explosive assay. The absorbance-concentration response was perfectly linear, and the limit of detection (LOD) of the procedure for both TATP and HMTD was approximately 0.2 mg L(-1). Neither common soil ions (Ca(2+), K(+), Cl(-), SO(4)(2-), Mg(2+) and NO(3)(-)) at 100-fold amounts nor military-purpose nitro-explosives of TNT, RDX, and PETN at 10-fold amounts interfered with the proposed assay. Active oxygen constituents of laundry detergents (perborates and percarbonates), which normally interfered with the assay, could easily be separated from the analytes by solubility differences. The method was statistically validated against standard reference methods of TiOSO(4) colorimetry and GC-MS.


Talanta | 2011

Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets

Erol Erçağ; Ayşem Üzer; Şule Eren; Şener Sağlam; Hayati Filik; Reşat Apak

Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analytical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro-aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998-0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1-0.5 μg. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determinations of TNT and tetryl.

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