Two types of bismuth modified electrodes, a bismuth-film modified glassy carbon (BiF-GCE) and a bismuth bulk modified carbon paste, were applied for the determination of selected nitroguanidine neonicotinoid insecticides. The method based on an ex situ prepared BiF-GCE operated in the differential pulse voltammetric (DPV) mode was applied to determine clothianidin in the concentration range from 2.5 to 23 μg cm−3 with a relative standard deviation (RSD) not exceeding 1.5%. The tricresyl phosphate-based carbon paste electrodes (TCP-CPEs), bulk modified with 5 and 20 w/w% of bismuth, showed a different analytical performance in the determination of imidacloprid, regarding the peak shape, potential window, and noise level. The TCP-CPE with 5% Bi was advantageous, and the developed DPV method based on it allowed the determination in the concentration range from 1.7 to 60 μg cm−3 with an RSD of 2.4%. To get a deeper insight into the morphology of the bismuth-based sensor surfaces, scanning electron microscopic measurements were performed of both the surface film and the bulk modified electrodes.

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Voltammetric behavior of erythromycin ethylsuccinate at a renewable silver-amalgam film electrode and its determination in urine and in a pharmaceutical preparation, Electrochimica Acta http://dx.2 Graphical abstract 3 Highlights  Voltammetric characterization of erythromycin ethylsuccinate (EES) on Hg(Ag)FE  Trace level determination of EES by electroreduction based SWV and SW-AdSV methods  Protonation of the tertiary amino group supports the adsorption of EES on Hg(Ag)FE  1 H NMR confirms chemical shifting of tertiary amine methyl proton signals with pH  Comparative HPLC-DAD measurements were performed for the validation of the methods 4 AbstractErythromycin, a macrolide antibiotic, has similar antimicrobial spectrum to penicillin and it is widely used, especially in the treatment of patients who are allergic to penicillin.In this work, the application of a renewable silver-amalgam film electrode (Hg (Ag)FE) for the characterization and determination of erythromycin ethylsuccinate (EES), a widely used esterified form of this antibiotic, by means of cyclic voltammetry (CV) and square wave voltammetry (SWV) is presented. In the aqueous Britton-Robinson buffer (pH 5.0-9.0) that served as the supporting electrolyte, one reduction peak of EES was observed in the investigated potential range between -0.75 V and -1.80 V vs SCE, with peak potential maxima ranging from -1.59 V to -1.70 V, which strongly depended on the applied pH, as did the peak shape. For the analytical purposes the pH of 7.0 was selected, since in this electrolyte the EES peak was well-shaped and separated from the background current of the supporting electrolyte in both cases; in the direct cathodic SWV and in the case of square wave adsorptive stripping voltammetry (SW-AdSV). It was established, by the Ep-pH correlation, that protons strongly influenced the electrochemical reduction of EES. The CVs recorded between 0.025 -0.50 V s -1 at pH 7.0 confirmed that the electrode reaction is adsorption-controlled. Based on the series of 1 H NMR measurements it is proved that the tertiary amino group of EES is mainly in its protonated form at pH 7.0 which may lead, at appropriate accumulation potential and time, to the favored adsorption of the target ionic form of the analyte improving on such way the sensitivity of the SW-AdSV method.The optimized procedures resulted in stable SWV responses with good linear correlation in the EES concentration range from 4.53 to 29.8 µg mL -1 (LOD = 1.36 µg mL -1 ), and from 0.69 µg mL -1 to 2.44 µg mL -1 (LOD 0.21 µg mL -1 ) in the case of optimized SWAdSV. The relative standard deviation is below 1.5%. The reliability of the elaborated procedures and thus the accuracy of the obtained results were validated by comparing them with those obtained by means of HPLC-DAD measurements. The direct cathodic SWV method was successfully applied for the determination of EES in the pharmaceutical preparation Eritromicin ® , while SW-AdSV was applied in the case of the spiked urine sample.In both cases, the standard addition meth...

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The renewable silver-amalgam film electrode (Hg(Ag)FE) was applied for voltammetric characterization and determination of semi-synthetic macrolide antibiotics azithromycin (AZI), clarithromycin (CLA) and roxithromycin (ROX) in the Britton-Robinson buffer as supporting electrolyte ranging the pH from 4.0 to 11.9. All three macrolides showed reduction signals in fairly negative potential range.During direct cathodic square wave voltammetric (SWV) investigations conducted over the potential range from À0.75 V to À2.00 V vs SCE, either one or two reduction peaks were obtained in the potential range from À1.5 to À1.9 V. The shapes and intensities of the signals depend on the applied pH values in wider pH ranges. For analytical purposes concerning the development of direct cathodic SWV and adsorptive stripping SWV (SW-AdSV) methods the neutral and slightly alkaline media were suitable as pH 7.2, pH 7.4 and pH 7.0 for AZI, CLA and ROX, respectively. Based on the cyclic voltammograms recorded at these pH values, adsorption-controlled electrode kinetics process can be proposed for all three macrolides. Furthermore, the water suppressed 1 H NMR measurements in the pH range between 6.0 and 10.5 indicated that the macrolide molecules at the optimal analytical conditions are predominantly in protonated form via their tertiary amino groups which supported in all three cases their adsorption on the appropriately polarized Hg(Ag)FE electrode. The optimized direct cathodic SWV methods showed good linearity in concentration ranges 4.81-23.3 mg mL À1 , 1.96-28.6 mg mL À1 and 1.48-25.9 mg mL À1 for AZI, CLA and ROX, respectively. The development of the SW-AdSV methods resulted in the linear responses at lower concentration ranges as 1.0-2.46 mg mL À1, 0.05-0.99 mg mL À1 and 0.10-0.99 mg mL À1 , for AZI, CLA and ROX, respectively. The relative standard deviation for all developed methods was not higher than 1.0% except the SWV method for AZI with 4.7%. In the case of all three investigated macrolide antibiotics the protonated form of the tertiary amino group(s) at appropriate accumulation potential and time favored the adsorption of the ionic form of the target molecules offering the opportunity for the development of SW-AdSV methods for their trace level analysis on Hg(Ag)FE. Optimized SW-AdSV method was applied for determination of ROX in pharmaceutical preparation Runac