Ibrahim Isildak

Determination of major phenolic compounds in water by reversed-phase liquid chromatography after pre-column derivatization with benzoyl chloride

A simple reversed-phase LC method capable of detecting ng/ml quantities of phenolic compounds in water is described. Pre-column derivatization with benzoyl chloride is used for the separation and determination o-cresol, m-cresol, p-cresol, phenol, resorcinol, catechol and hydroquinone in water. The benzoyl derivatives formed within in 15 min, were extracted with dietyl ether, and then analyzed by liquid chromatography with UV detection at 232 nm. With a mobile phase of acetonitrile-tetrahydrofuran-water (54:6:40, v/v) the seven derivatives were eluted in 15 min. The detection limits were between 0.05 and 0.50 ng/ml for 50 ml of a standard water sample. The method was applied to the analysis of phenols in wine and river water. The recovery of the derivatives from pure water was 81-94% with relative standard deviations of 2.5-5.0%.

Simultaneous detection of monovalent anions and cations using all solid-state contact PVC membrane anion and cation-selective electrodes as detectors in single column ion chromatography

The overall efficiency of ion chromatographic procedures allows the possibility of routine separation and detection of common inorganic and organic anions and cations at low levels in a simultaneous system. A simple and rapid independent separation, and sensitive simultaneous detection of monovalent common anions and cations were achieved using 2 mM copper sulfate, (at pH: 5.40), as eluent with low cell-volume potentiometric detectors. This was established using all-solid state contact, tubular, PVC-matrix membrane anion and cation-selective electrodes in series as detectors with mixed-bed ion-exchange column in ion chromatography. The developed method is reproducible and highly selective to monovalent anions and cations, and takes less than 8 min. Under all operation conditions, the detection limits of the developed method, for potassium, rubidium, cesium, thallium(I), nitrite, nitrate, benzoate and bromide, were of the order of tens of ppb, for sodium, ammonium, chloroacetate, cyanate and chloride ions, values were of the order of hundreds of ppb for an injected volume of 20 mul. The method was flexible since most of anions do not interfere the detection of cations and most of cations do not affect the detection of anions, so that the method can be applied to many sample types e.g. environmental. The application of the method for river, sea and tap water samples were illustrated.

Measuring calcium, potassium, and nitrate in plant nutrient solutions using ion-selective electrodes in hydroponic greenhouse of some vegetables.

Generally, the life cycle of plants depends on the uptake of essential nutrients in a balanced manner and on toxic elements being under a certain concentration. Lack of control of nutrient levels in nutrient solution can result in reduced plant growth and undesired conditions such as blossom‐end rot. In this study, sensitivity and selectivity tests for various polyvinylchloride (PVC)‐based ion‐selective membranes were conducted to identify those suitable for measuring typical concentration ranges of macronutrients, that is, NO3−, K+, and Ca2+, in hydroponic solutions. The sensitivity and selectivity of PVC‐membrane‐based ion‐selective sensors prepared with tetradodecylammoniumnitrate for NO3−, valinomycin for K+, and Ca ionophore IV for Ca2+ were found to be satisfactory for measuring NO3−, K+, and Ca2+ ions in nutrient solutions over typical ranges of hydroponic concentrations. Potassium, calcium, and nitrate levels that were utilized by cucumber and tomato seedlings in the greenhouse were different. The findings show that tomato plants consumed less amounts of nitrate than cucumber plants over the first 2 months of their growth. We also found that the potassium intake was higher than other nutritional elements tested for all plants.

Calcium, potassium and nitrate in plant nutrient solutions by measuring of with ion‐selective electrodes in hydroponic green house of some vegetables

Generally, the life cycle of plants depends on the uptake of essential nutrients in a balanced manner and on toxic elements being under a certain concentration. Lack of control of nutrient levels in nutrient solution can result in reduced plant growth and undesired conditions such as blossom‐end rot. In this study, sensitivity and selectivity tests for various polyvinylchloride (PVC)‐based ion‐selective membranes were conducted to identify those suitable for measuring typical concentration ranges of macronutrients, that is, NO3−, K+, and Ca2+, in hydroponic solutions. The sensitivity and selectivity of PVC‐membrane‐based ion‐selective sensors prepared with tetradodecylammoniumnitrate for NO3−, valinomycin for K+, and Ca ionophore IV for Ca2+ were found to be satisfactory for measuring NO3−, K+, and Ca2+ ions in nutrient solutions over typical ranges of hydroponic concentrations. Potassium, calcium, and nitrate levels that were utilized by cucumber and tomato seedlings in the greenhouse were different. The findings show that tomato plants consumed less amounts of nitrate than cucumber plants over the first 2 months of their growth. We also found that the potassium intake was higher than other nutritional elements tested for all plants.

Electrochemical Determination of Copper(II) in Water Samples Using a Novel Ion-Selective Electrode Based on a Graphite Oxide–Imprinted Polymer Composite

ABSTRACT A novel copper(II)-selective electrode based on graphite oxide/imprinted polymer composite was developed for the electrochemical monitoring of copper(II) (Cu2+) ions. The electrode exhibited highly selective potentiometric response to Cu2+ with respect to common alkaline, alkaline earth and heavy metal cations. The composite composition studies indicated that the most suitable composite composition performing the most promising potentiometric properties was 20.0% ionophore (Cu2+-ion imprinted polymer), 10.0% paraffin oil, 5.0% multiwalled carbon nanotubes, and 65.0% graphite oxide. The fabricated electrode exhibited a linear response to Cu2+ over the concentration range of 1.0 × 10− 6–1.0 × 10− 1 M (correlation coefficient of 0.9998) with a sensitivity of 26.1 ± 0.9 mV decade− 1. The detection limit of the fabricated electrode was determined to be 4.0 × 10− 7 M. The electrode worked well in the pH range of 4.0–8.0. The electrode had stable, reversible and fast potentiometric response (3 s). In addition, the electrode had a lifetime of more than 1 year. The analytical applications of the proposed electrode were performed using as an indicator electrode for the potentiometric titration of Cu2+ with ethylene diamine tetraacetic acid solution and for the determination of Cu2+ of spiked river, dam, and tap water samples. The obtained results for potentiometric titration and water samples were satisfactory.

Simultaneous Analysis of Monovalent Anions and Cations with a Sub-Microliter Dead-Volume Flow-Through Potentiometric Detector for Ion Chromatography

A microliter dead-volume flow-through cell as a potentiometric detector is described in this article for sensitive, selective and simultaneous detection of common monovalent anions and cations in single column ion chromatography for the first time. The detection cell consisted of less selective anion- and cation-selective composite membrane electrodes together with a solid-state composite matrix reference electrode. The simultaneous separation and sensitive detection of sodium (Na(+)), potassium (K(+)), ammonium (NH4 (+)), chloride (Cl(-)) and nitrate (NO3 (-)) in a single run was achieved by using 98% 1.5 mM MgSO4 and 2% acetonitrile eluent with a mixed-bed ion-exchange separation column without suppressor column system. The separation and simultaneous detection of the anions and cations were completed in 6 min at the eluent flow-rate of 0.8 mL/min. Detection limits, at S/N = 3, were ranged from 0.2 to 1.0 µM for the anions and 0.3 to 3.0 µM for the cations, respectively. The developed method was successfully applied to the simultaneous determination of monovalent anions and cations in several environmental and biological samples.

Investigation of ischemia modified albumin, oxidant and antioxidant markers in acute myocardial infarction

Introduction Acute myocardial infarction (AMI) is still one of the most common causes of death worldwide. In recent years, for diagnosis of myocardial ischemia, a new parameter, called ischemia modified albumin (IMA), which is thought to be more advantageous than common methods, has been researched. Aim In this study, systematic analysis of parameters considered to be related to myocardial ischemia has been performed, comparing between control and myocardial ischemia groups. Material and methods We selected 40 patients with AMI and 25 healthy controls for this study. Ischemia modified albumin levels, glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) antioxidant enzyme activities and non-enzymatic antioxidants such as retinol, α-tocopherol, β-carotene and ascorbic acid levels were investigated in both groups. Glutathione (GSH) and malondialdehyde (MDA) levels, which are indicators of oxidative stress, were compared between patient and control groups. Results Ischemia modified albumin levels were found significantly higher in the AMI diagnosed group when compared with controls. The MDA level was elevated in the patient group, whereas the GSH level was decreased. SOD, GPx and CAT enzyme levels were decreased in the patient group, where it could be presumed that oxidative stress causes the cardiovascular diseases. Conclusions Due to the increased oxidative stress, non-enzymatic and enzymatic antioxidant capacity was affected. Systematic investigation of parameters related to myocardial infarction has been performed, and it is believed that such parameters can contribute to protection and early diagnosis of AMI and understanding the mechanism of development of the disease.

Novel creatine biosensors based on all solid-state contact ammonium-selective membrane electrodes

Abstract Novel creatine bienzymatic potentiometric biosensors were prepared by immobilizing urease and creatinase on all solid-state contact PVC-containing palmitic acid and carboxylated PVC matrix membrane ammonium-selective electrodes without inner reference solution. Potentiometric characteristics of biosensors were examined in physiological model solutions at different creatine concentrations. The linear working range and long-term sensitivity of the biosensors were also determined. The creatine biosensors prepared by using the carboxylated PVC membrane electrodes showed more effective performance than those of the PVC containing palmitic acid membrane electrodes. Creatine assay in serum samples was successfully carried out by using the standard addition method.

New sensor based on membranes with magnetic nano-inclusions for early diagnosis in periodontal disease

A series of sodium selective membranes with magnetic nano-inclusions using p-tertbutyl calix[4]arene as ionophore and polymeric matrix (polyvinyl chloride) have been developed, and the corresponding sodium selective sensors were obtained for the first time. A linear range was registered between 3.1 × 10-5 and 10-1moldm-3 and near Nernstian electrochemical answer: 55.73mV/decade has been recoreded for PVC (polyvinyl chloride) - based sodium selective sensor, with a response time of 45s. Due to their small dimensions, sensors could be used for measuring ions from the gingival crevicular fluid directly into the peri-odontal pocket, avoiding the difficulties of collecting an appropriate amount of fluid for analysis. Alterations in the inorganic ions level could be evidenced with this new device, assisting the early diagnosis and prevention of periodontal disease.

Green synthesis of silver nanoparticles using Thymbra spicata L. var. spicata (zahter) aqueous leaf extract and evaluation of their morphology-dependent antibacterial and cytotoxic activity

Abstract Silver (Ag) nanoparticles (NPs) were green synthesized at room temperature using different concentrations of the Thymbra spicata L. var. spicata (Zahter) aqueous leaf extracts for the first time. With the synthesis of AgNPs using the leaf extract of Cynara scolymus (Artichoke) and Mentha piperita (Peppermint), the biological activities of the nanoparticles synthesized using leaf extract of three economically significant plants have been studied comparatively. Nanoparticles were characterized by different spectroscopic and microscopic analysis. TEM analysis of the biosynthesized AgNPs revealed that the size and shape of the AgNPs were changed with the plant extract concentration. Biologically synthesized AgNPs from leaf extracts of the three different plants displayed significant differences in antibacterial activity against two different gram-negative and gram-positive bacteria. Also, the results from this study show the shape dependence of the antibacterial and cytotoxic activity of silver nanoparticles synthesized using T. spicata leaf extract. The nanoparticles with different shapes exhibited the strongest antibacterial and cytotoxic activity compared to mostly spherical nanoparticles. Present results clearly indicate that biological activities of silver nanoparticles were affected by nanoparticle shape and the source of the plant extract used in the synthesis.