Comparison of selectivity and sensitivity of various ferric selective electrodes prepared using N-((bis(dimethyl amino)methylene)carbamothioyl)benzamide

N-((Bis(dimethyl amino)methylene)carbamothioyl)benzamide (NBMCB) was synthesized, characterized, and used as an ionophore for producing three novel ion-selective potentiometric sensors for Fe(III) determination. Firstly, using the molecular mechanic-based MMFF94 method, the most stable NBMCB's conformer and its isosteric complexes with various cations were determined. According to the Gibbs free energy results of the reaction, the thermodynamic complexation reactivity of Fe(III) and the ligand was acceptable. These results were obtained using the B3LYP approach and the 6-31G(d,p) basis set that was substituted for heavy metals by the LanL2DZ basis set. We used UV-visible spectrophotometry to confirm the tendency of NBMCB to react with Fe(III). Generally, three diverse liquid membrane ferric selective electrodes were obtained by the use of the specified ligand: classic with a liquid internal electrolyte-ferric selective electrode (LIE-FSE), solid state-FSE (SS-FSE), and coated wire-FSE (CW-FSE). The reactions exhibited Nernstian behavior across all electrodes. The limit of detection was enhanced for the SS-FSE (3 × 10-9 M) and the CW-FSE (3 × 10-7 M) in comparison with that of the LIE-FSE (7 × 10-7 M). The lifetime of the LIE-FSE was 8 weeks, while it was 10 weeks for the SS-FSE and the CW-FSE. Elimination of the internal solution reduced the limit of detection and prolonged the lifespan of the sensors. Also, the three electrodes all had a short response time of around 5-7 s. The sensors were utilized as indicator electrodes during the potentiometric titration of Fe(III) using ethylenediaminetetraacetic acid.

Fast chromium determination in pharmaceutical tablets by using electrochemical sensors: Preparation and comparison

In the present paper, three electrodes were prepared with the aim of detecting chromium (III) in pharmaceutical tablets and comparing their capabilities and efficiency. At first, N-(pyridine-2-ylcarbamothioyl) benzamide (NP2YCTB) was synthesized and characterized by 1H NMR, FTIR, and 13C NMR spectroscopy methods. Then, it is used as a sensing material to prepare three types of chromium potentiometry sensors including solid-state electrodes (SSE), coated wire electrodes (CWE) as asymmetric electrodes, and liquid membrane electrodes (LME) as symmetric electrodes. The responses of all electrodes were Nernstian. Field-emission scanning electron microscopy was utilized to investigate the liquid membrane morphology. The presence of chromium (III) in the membrane was proved using Energy-dispersive X-ray spectroscopy and the coordination of NP2YCTB heteroatoms with chromium (III) was confirmed by Fourier transform infrared spectroscopy. The limit of detection for SSE (3 × 10-9 mol/L) was enhanced compared with LME (7 × 10-6 mol/L) and CWE (3 × 10-7 mol/L). The response time of electrodes was very short so it was about 5-6 s for LME and CWE and 5-8 s for SSE. The sensors were used for the potentiometric determination of chromium (III) in pharmaceutical tablets and in the potentiometric titration of it with EDTA.

Chromium measurement in pharmaceutical samples: a comparative study of three new membrane electrodes with different electron-ion exchangers

The present study deals with synthesis of N-(thiazol-2-ylcarbamothioyl) benzamide. It was utilized as a neutral ionophore for designing three types of chromium(III) sensors including coated wire ion selective electrodes (CW-ISEs), ion selective electrodes with liquid internal electrolyte (LIE-ISEs), and solid-state ion selective electrodes (SS-ISEs). UV-visible spectrophotometry was used to confirm the affinity of N-(thiazol-2-ylcarbamothioyl) benzamide to chromium(III). It was found that a membrane with a composition of 2% NaTPB, 8% ionophore, 60% DBP, and 30% PVC showed the best performance and a Nernstian slope of 21.6 mV per decade. Scanning electron microscopy was used to assess the PVC membrane morphology. The existence of chromium(III) in the liquid membrane matrix was proved by energy-dispersive X-ray spectroscopy. Detection limits for SS-ISE (1 × 10^-6 M) and CW-ISE (1 × 10^-6 M) were enhanced relative to LIE-ISE (1 × 10^-5 M). All three electrodes showed a response time of about 5 s. The sensors' applicable pH range was 4.0-6.0. Fourier transform infrared spectra recorded through the electrode membrane showed that chromium(III) ion can interact with sulfur, nitrogen and oxygen atoms of N-(thiazol-2-ylcarbamothioyl) benzamide. The sensors were utilized as indicator electrodes in chromium(III) potentiometric titration with ethylenediaminetetraacetic acid and for directly measuring chromium(III) in some pharmaceutical samples.

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).