Electrochemical Sensing of Tryptophan and Tyrosine in Chronic Kidney Disease Patients Using Magnetic Core/Ag Nanoparticles Shell Nanocomposite Modified Electrode

Journal of Analytical Chemistry - This paper reports the production of a novel magnetic nanocomposite based on core-shell Fe3O4@Ag nanoparticles. Fe3O4@Ag nanoparticles were used to fabricate a...     

Adsorptive Stripping Differential Pulse Voltammetric Determination of Risperidone with a Multi‐Walled Carbon Nanotube‐Ionic Liquid Paste Modified Glassy Carbon Electrode

A new composite electrode has been fabricated based on coating multi‐walled carbon nanotubes (MWCNTs) and n‐octylpyridinum hexafluorophosphate (OPPF₆) ionic liquid composite on a glassy carbon (GC) electrode (OPPF₆‐MWCNTs/GCE). This electrode shows very attractive electrochemical performances for electrooxidation of risperidone (RIS) compared to conventional electrodes using carbon and mineral oil, notably improved sensitivity and stability. The oxidation peak potentials in cyclic voltammogram of RIS on the OPPF₆‐MWCNTs/GCE was occurred around 230 mV vs. SCE at Britton–Robinson (B–R) buffer (pH 4.0) at scan rate of 100 mV s^?1. The electrochemical parameters such as diffusion coefficient (D), charge transfer coefficient (α) and the electron transfer rate constant (k/_s) were determined using cyclic voltammetry. Under the optimized conditions, the peak current was linear to risperidone concentration over the concentration range of 10–200 nM with sensitivity of 0.016 μA/nM^?1 using differential pulse voltammetry. The detection limit was 6.54 nM (S/N = 3). The electrode also displayed good selectivity and repeatability. In the presence of clozapine (CLZ) the response of RIS kept almost unchanged. Thus this electrode could find application in the determination of RIS in some real samples. The analytical performance of the OPPF₆‐MWCNTs/GCE was demonstrated for the determination of RIS in human serum and pharmaceutical samples.     

The potentiometric behavior of polymer-supported metallophthalocyanines used as anion-selective electrodes

Liquid polymer membrane electrodes based on nickel and manganese phthalocyanines were examined for use as anion-selective electrodes. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) membranes, which were directly coated onto the surfaces of graphite electrodes. The resulting electrodes demonstrate near-Nernstian responses over a wide linear range of perchlorate anion (5 × 10⁻⁷ to 1 × 10⁻¹ M). The electrodes have a fast response time, submicromolar detection limits (5 × 10⁻⁷ M perchlorate), and could be used over a wide pH range of 3.5–10. The influences of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The proposed sensors revealed high selectivity for perchlorate over a number of common inorganic and organic anions. The highest selectivity was observed for the electrode based on manganese phthalocyanine in the presence of the lipophilic anionic additive sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. Application of the electrodes to determine perchlorate in tap water and human urine is also reported.      

Determination of cadmium and zinc in water samples by flame atomic absorption spectrometry after cloud-point extraction

The phase-separation phenomenon of nonionic surfactants occurring in an aqueous solution was used for the extraction of Cd and Zn from water samples. After complexation with 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) in hydrochloric acid medium (pH 1), the analytes were quantitatively extracted after centrifugation into the phase rich in the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X-114). Tetrahydrofuran acidified with 0.1 M HCl was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry. The adopted concentrations for NDDBH, Triton X-114 and hydrochloric acid were all optimized. Detection limits (3σ) of 0.33 and 0.85 ng/mL along with enrichment factors of 157 and 118 for Cd and Zn, respectively, were achieved. The proposed method was applied to the determination of Cd and Zn in acidic solutions of certified reference materials. A comparison with certified values was performed for an evaluation of the accuracy, resulting in a good agreement according to the t-test at a 95% confidence level. The high efficiency of the cloud-point extraction to carry out the determination of the studied analytes in complex matrices was, therefore, demonstrated. The text was submitted by the authors in English.     

Chemoselective Solvent-free Deoximation by (NH4)2Cr2O7 in the Presence of ZrCl4 on Wet SiO2

Russian Journal of Organic Chemistry -     

Enhanced Electrocatalytic Reduction of Oxadiargyl and Its Determination on 2‐(4‐((4‐Acetylphenyl)diazenyl)phenylamino)‐ethanol Modified Graphene‐Paste Electrode

The electrochemical behavior of oxadiargyl at a graphene‐paste electrode modified with an azo dye, 2‐(4‐((4‐acetylphenyl)diazenyl)phenylamino)ethanol (ADPE), ADPE/MGRPE was investigated. The modified electrode showed high electrocatalytic activity toward oxadiargyl. The apparent electron transfer rate constant (k_s) and charge transfer coefficient (α) between electrode and ADPE were 1.16 s^?1 and 0.41, respectively. The differential pulse voltammetry response of the modified graphene‐paste electrode was linear against the concentration of oxadiargyl in the range from 0.03 to 1.4 mg L^?1. The limit of detection was found to be 1.3 µg L^?1 (S/N=3). The practical analytical utility of this electrode was demonstrated by measurement of oxadiargyl in river water, soil and rice samples.