Synthesis of nanosized sulfate-modified α-Fe2O3 and its use for the fabrication of all-solid-state carbon paste pH sensor

Selective and ultrasensitive citric acid assay in urine samples using a MWCNT/Fe3O4 nanoparticle-modified carbon paste electrode

A carbon paste electrode (CPE) modified with multiwalled carbon nanotubes and magnetite nanoparticles is introduced (CNT/Fe₃O₄-CPE) as the most sensitive citric acid (CA) electrochemical sensor reported so far. The structural and spectroscopic characterization by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy is presented. The electrocatalytic performance of the electrode was substantiated using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Performing voltammetric experiments at different pH values and various scan rates gave some evidence for the electro-oxidation mechanism of CA. The EIS study gave an obvious indication for the enhancement of the charge transfer rate of CA by the nanocomposite. Various parameters affecting the electrode performance were studied. Using differential pulse voltammetry it was found that the CNT/Fe₃O₄-CPE showed a linear dynamic range of 5.0 × 10^-7-1 × 10^-4 mol L^-1, an excellent sensitivity of 5184 μA mM^-1 cm^-2, and a detection limit of 3.6 × 10^-7 mol L^-1 for CA determination. The relative standard deviation was found to be 3.1% (n = 3). The method was utilized for CA determination in urine samples without utilizing complicated sample pretreatment.

A comparative study on selectivity and sensitivity of new chromium and copper electrodes

4-Methylcoumarin-7-yloxy-N-phenyl acetamide and 4-methylcoumarin-7-yloxy-N-4-nitrophenyl acetamide were synthesized and used as new ionophores in the carbon paste matrix to produce two novel potentiometric modified electrodes. The selectivity of the electrode changed from copper (II) to chromium (III) with the addition of a nitro group to the phenyl ring of the ionophore. The ionophores’ tendency to ions was confirmed by UV–visible spectrophotometry. Both electrodes were modified by multi-walled carbon nanotubes (MWCNTs) as an excellent modifier of carbon paste electrode (CPE). The best sensor response in the case of copper (II) selective CPE was obtained by 5% ionophore, 65% graphite powder, 5% MWCNT, and 25% paraffin oil. In addition, in the case of chromium (III) selective CPE, these conditions are 20% ionophore, 50% graphite powder, 5% MWCNT, and 25% paraffin oil. The copper (II) selective CPE showed a Nernstian slope of 32.15 mV/decade within the concentration range of 1.0 × 10^–10–1.0 × 10^–1 mol L⁻¹, while chromium (III) selective CPE showed a Nernstian slope of 19.28 mV/decade over the concentration range of 1.0 × 10^–10–7.0 × 10^–3 mol L⁻¹. The electrodes have short response time of less than 5 s and were used successfully to determine copper (II) in wastewater and to speciation of chromium (III) and chromium (VI).

A novel chloride selective potentiometric sensor based on graphitic carbon nitride/silver chloride (g-C3N4/AgCl) composite as the sensing element

In this research, AgCl anchored graphitic carbon nitride (g-C₃N₄) was introduced as a novel potentiometric sensing element. A g-C₃N₄/AgCl-modified carbon paste electrode (CPE) was fabricated and used as an outstandingly selective potentiometric sensor to determine Cl^- in water samples. The g-C₃N₄/AgCl nanocomposite was characterized with SEM, XRD and FT-IR techniques. It was demonstrated that, the incorporation of 5% of g-C₃N₄/AgCl, as a chloride ionophore in a CPE, results in a stable potential response of the electrode to chloride ion. The Nernstian slope of the electrode response was 55.4 (±0.3) mVdecade^-1, over a wide linear concentration range of 1 × 10^-6-1 × 10^-1 mol L^-1 and the detection limit of the electrode was estimated to be 4.0 × 10^-7 mol L^-1. The g-C₃N₄/AgCl-modified CPE electrode provided fast response time and long-term stability (more than 2 months) while the potential interfering ions such as I^-, Br^-, and CN^- showed no significant effect on the potential response. Since these interfering ions affected the response of the CPE electrode, modified with AgCl, highlighting the interesting effect of g-C₃N₄ on the sensor performance. This innovative electrode was shown to be a sensitive and accurate sensor for chloride ion content estimation in water samples.

Molecularly imprinted polymers in toxicology: a literature survey for the last 5 years

The science of toxicology dates back almost to the beginning of human history. Toxic chemicals, which are encountered in different forms, are always among the chemicals that should be investigated in criminal field, environmental application, pharmaceutic, and even industry, where many researches have been carried out studies for years. Almost all of not only drugs but also industrial dyes have toxic side and direct effects. Environmental micropollutants accumulate in the tissues of all living things, especially plants, and show short- or long-term toxic symptoms. Chemicals in forensic science can be known by detecting the effect they cause to the body with the similar mechanism. It is clear that the best tracking tool among analysis methods is molecularly printed polymer-based analytical setups. Different polymeric combinations of molecularly imprinted polymers allow further study on detection or extraction using chromatographic and spectroscopic instruments. In particular, methods used in forensic medicine can detect trace amounts of poison or biological residues on the scene. Molecularly imprinted polymers are still in their infancy and have many variables that need to be developed. In this review, we summarized how molecular imprinted polymers and toxicology intersect and what has been done about molecular imprinted polymers in toxicology by looking at the studies conducted in the last 5 years.

Graphitic carbon nitride (g-C3N4)/graphite nanocomposite as an extraordinarily sensitive sensor for sub-micromolar detection of oxalic acid in biological samples

Nanosized graphitic carbon nitride (nano-g-C₃N₄) was synthesized using the thermal polymerization of melamine and utilized as a novel electrocatalyst for electrooxidation of oxalic acid (OA).