This study aims to synthesize gold nanoparticles/biphenol–biphenoquinone (AuNPs−BOH−BQ) and to study its application as a novel heterogeneous electron transfer mediator to modify carbon paste electrode (CPE/Au NPs−BOH−BQ) for ultra‐trace determination of captopril (CP). Characterization results show well dispersed Au NPs with sizes in the range of 8.0–10.5 nm. Under optimized conditions, the calibration plot was linear from 1 to 5×104 nM (two segments, 1–150 nM and 0.15–50.0 μM) and the detection limit was calculated to be 0.4 nM (S/N=3). Finally, the suggested sensor showed stable and reliable responses to CP in CP pharmaceutical tablet and urine samples.

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This paper reports the preparation of multiwalled carbon nanotubes/4,4′‐dihydroxybiphenyl (MWCNTs‐DHB) nanolayered composite as a new modifier for modification of carbon paste electrode (CPE/MWCNTs‐DHB). CPE/MWCNTs‐DHB shows linear responses for phenol in the concentrations range of 0.04–220 μM with a current sensitivity of 0.67 μA μM−1 and a detection limit of 8.0 nM (S/N=3). The electrode shows high selectivity, good repeatability (RSD=4.1 %), excellent reproducibility (RSD=3.5 %), and acceptable stability (91.2 % over one‐month storage). Moreover, the modified CPE exhibits appreciable recoveries (93.0–104.0 %) indicating its acceptable performance for determination of phenol in tap and river water samples.

For the first time, the [Sr(OH 2 ) 4 (phen-dione) 2 ](Cl) 2 complex (Sr-Phen) was synthesized and characterized by different spectroscopy techniques such as 1 H-NMR, UV-Vis, FT-IR and conductometry as well as elemental analysis. The prepared complex was used for modification of graphite paste electrode for simultaneous determination of 4-aminophenol (AP), uric acid (UA), and tryptophan (Trp). Detailed investigations by electrochemical impedance spectroscopy and electrochemistry methods were used in order to elucidate the properties of the modified graphite paste electrode with Sr-Phen. The proposed modified electrode displays intense and indelible electrooxidation responses for simultaneous determination of AP, UA, and Trp to three well-separated peaks in potential range from 0.4 to 1.1V using cyclic and differential pulse voltammetry methods in pH 2.0. Based on the experimental results the detection limits of 3.40, 1.06 and 1.32 µM were obtained for AP, UA and Trp, respectively. Finally, the proposed modified electrode was used for simultaneous determination of AP, UA and Trp in real samples.

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