Topcu, Cihan; Caglar, Bulent; Guner, Eda Keles; Coldur, Fatih; Caglar, Sema; Yıldırım, Özden; Volkan Özdokur, Kemal; Cubuk, Osman

A folic acid-functionalized carbon nanotube nanomaterial was prepared by immobilizing folic acid molecules on the carbon nanotubes through covalent bonds. The material was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy. Fourier transform infrared spectroscopy confirmed that folic acid molecules were grafted on the carbon nanotube surfaces through the amide bonds between the carboxylic acid functional groups of the oxidized carbon nanotubes and the amine groups of the folic acid molecules. The folic acid molecules bonded to carbon nanotube surfaces led to appreciable changes in the morphology. By using currently obtained folic acid-functionalized carbon nanotube nanomaterial as electroactive material in a polyvinyl chloride membrane, a potentiometric copper (II)-selective sensor was developed. Membrane optimization studies showed that the composition exhibiting the best potentiometric properties was 4.0% (w/w) folic acid–carbon nanotube, 64.0% (w/w) o-nitrophenyl octylether, and 32.0% (w/w) polyvinyl chloride. The developed sensor displayed a linear response in the copper (II) concentration ranging from 1.0 × 10–6 to 1.0 × 10–1 M with a correlation coefficient of 0.9993 and a slope of 29.8 ± 0.6 mV/decade of activity. The response time, detection limit, and pH working range were determined to be 4 s, 3.8 × 10–7 M and 4.0–8.0, respectively. The developed sensor showed highly selective and satisfactory potentiometric response for the determination of copper (II) in a Turkish coin.

Kardaş, Faruk

A novel Schiff base designated as 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole was synthesized and characterized. A polyvinyl chloride-membrane potentiometric copper(II)-selective sensor was prepared by using the synthesized 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole compound. The prepared polyvinyl chloride-membrane copper(II)-selective sensor exhibited very good selectivity and sensitive potentiometric response towards copper(II) ions compared to a wide variety of other cations. The sensor had a fast response time of <5 s, and showed a linear Nerstian behavior to copper(II) ions over a wide concentration range from 1.0 × 10−5 to 1.0 × 10−1 mol L−1 with a slope of 29.2 ± 0.7 and correlation coefficient of 0.9998. The prepared polyvinyl chloride-membrane copper(II)-selective sensor was used for 14 weeks without any significant change in its potentiometric response. The potentiometric response of the developed sensor was highly repeatable. Additionally, the developed sensor was used as an indicator electrode for the potentiometric titration of copper(II) ion with ethylenediaminetetraacetic acid. The sensor was also successfully applied to the direct determination of copper(II) ions in tap water, river water, and dam water samples.

Özdokur, Kemal Volkan; Engin, Esra; Yengin, Çiğdem; Ertaş, Hasan; Ertaş, F. Nil

Modern treatments o Parkinson’s disease include the use of carbidopa and droxidopa along with levodopa that demonstrates the necessity for their binary and simultaneous determination in pharmaceutical tablets and biological matrices. This study presents a rapid, accurate, and precise method for the simultaneous determination of these analytes by liquid chromatography–tandem mass spectrometry method for the first time. Accordingly, performances of two types of analytical columns, namely, octadecylsilane and hydrophilic interaction liquid chromatographic columns, were tested and better resolution was obtained with the former. The pH of aqueous mobile phase (0.5% formic acid) was adjusted to 2.3 to ensure the analytes were in molecular form. Calibration graphs were obtained using multiple reaction mode and detection limits were in the region from 0.002 to 0.007 μM for both columns. The method developed was applied for quality control samples and tablets and satisfactory recovery values from 100 to 106% were obtained.

Topcu, Cihan; Lacin, Gamze; Yilmaz, Vedat; Coldur, Fatih; Caglar, Bulent; Cubuk, Osman; Isildak, Ibrahim

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.