A carbon nanotubes modified silver electrode (CNTs-Ag) was prepared via catalytic chemical vapor deposition and characterized. The morphology, crystallinity, elemental composition, and other quality parameters of the prepared electrode were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman techniques. The characterization results revealed the modification of the silver metal surface with CNTs of good characteristics. A sequential injection analysis (SIA) system was developed for studying the reaction of ascorbic acid with KIO₃ using the prepared CNTs-Ag electrode. Electrodes were polarized with both direct current (DC) and periodic square wave (SW). Various experimental conditions affecting the differential electrolytic potentiometric (DEP) peak such as current density, SW bias value, and flow rate were appraised. Under the optimum conditions, good linear responses for ascorbic acid were obtained in the range of 60.0–850.0 µM for both types of polarization with detection limits of 14.0–19.0 µM. The results obtained showed that the periodic polarization method was more sensitive than DC polarization and the electrode response was faster. Ascorbic acid in pharmaceutical tablets was determined with satisfactory results using this method. The prepared CNTs-based electrode exhibited good performance for a long period of use. The method is simple, rapid, and inexpensive for routine analysis.

This work reports the use of carbon nanotubes-modified silver (CNTs-Ag) electrode prepared by chemical vapor deposition (CVD) as indicating system in differential electrolytic potentiometry (DEP) for both redox and precipitation reactions. Characterization of CNTs-Ag electrode by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed the formation of aligned CNTs of a good degree of crystallinity and well-graphitized sheets. CNTs-Ag electrode was applied successfully for the determination of ascorbic acid in both pure form and in pharmaceutical and food samples along with in the determination of cyanide too down to quite low concentrations. CNTs-Ag electrode exhibited a fast and stable response and attained equilibrium in a short time. These good characteristics are attributed to the rapid heterogeneous electron transfer and high electrode surface area offered by CNTs. Additionally, modification of the Ag with CNTs grown via CVD method offers adhesion of the CNTs layers to the Ag surface and direct electrical contact better than the external modification methods commonly used such as casting the CNTs or mixing them with Nafion. Moreover, CVD method offers the chance to produce aligned CNTs that have better electrical properties than the randomly distributed ones. This work also proposed a CNTs growth mechanism by XPS depth profiling analysis. Figure 1

Metallic electrodes modified with carbon nanotubes (CNTs) by direct growth have advantages over the ones modified through external connection methods. These advantages are: (i) reduced contact resistance between CNTs and metal substrate, which is required for electroanalytical determinations. (ii) Strong adhesion of the CNTs layer to the metal substrate which in turn prevents the detachment of CNTs from the electrode surface and stops the deterioration of the signal with time and use. This present work shows the use of carbon nanotubes-modified silver (CNTs-Ag) electrode prepared by direct growth of CNTs as indicator electrodes for differential electrolytic potentiometric (DEP) determination of the fluoroquinolone antibiotic, ciprofloxacin. Characterization of CNTs-Ag electrode by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy showed the growth of aligned, crystalline, and graphitized CNTs. Application of CNTs-Ag electrode for the determination of ciprofloxacin by sequential injection analysis (SIA) method exhibited fast and stable response, reproducible signals, and durability for long-term use. Ciprofloxacin has been quantified in the range of 60 – 1000 µmol/L with a good linear relationship. This work combined the advantages of Direct grown CNTs, SIA technique, and the square-wave DEP method. Figure 1

This work reports the development of a new robust electrode composed of carbon nanotubes (CNTs) for redox potentiometry to determine ascorbic acid. The electrode was fabricated via catalytic chemical vapor deposition (CVD) of ethylene on Ag substrate in the presence of H₂ gas at 800 °C. The C₂H₂:H₂ ratio was 75:90 ml/min respectively. The prepared electrode was characterized with SEM, TEM, XRD, XPS, and Raman spectrometry. SEM showed the formation of aligned CNTs. XRD and Raman spectrometry proved the formation of CNTs with a good degree of graphitization and high crystallinity. XPS analysis results showed 80% of SP² C–C with a small presence of carbonyls and carboxylates, indicating the high perfection of the CNTs formed. CNT/Ag electrode was applied, for the first time, to zero-current potentiometry and was successfully used to determine ascorbic acid in both pure form and in pharmaceutical formula. Ascorbic acid concentrations down to 0.5 mmol/L was determined. Sigmoidal potentiometric curves were obtained and the results were comparable to those obtained from Pt electrode. The CNT/Ag electrode attained fast equilibrium and exhibited good sensitivity and reproducibility. The enhanced sensing efficiency is attributed to the rapid heterogeneous electron transfer and high electrode surface area offered by CNTs grown via CVD. Additionally, the CVD method produced CNT/Ag electrode with strong adhesion of the CNTs layer to the substrate compared to other CNT-based electrodes prepared by casting the CNTs or mixing them with Nafion. This in turn improves the performance and durability. Moreover, unlike the Pt electrode, the CNT on the surface of this electrode may easily be functionalized by immobilizing the desired moieties via various types of strategies to suit different selective routine applications. Figure 1

Fabrication and application of a robust carbon nanotube-modified silver (CNT/Ag) electrode prepared via catalytic chemical vapor deposition (CVD) of ethylene is presented. The process resulted in aligned, multiwalled, graphitized CNTs with high crystallinity, as confirmed by SEM, TEM, XRD, and Raman spectroscopy. XPS analysis revealed a dominant sp² C–C composition, indicating the high structural perfection of the CNTs. The direct growth of CNTs on the Ag substrate offered strong adhesion and reduced contact resistance, outperforming conventional modification methods like casting or mixing with Nafion. The CNT/Ag electrode demonstrated excellent electrochemical properties, including fast equilibrium, stable response, reproducibility, and long-term durability. These features are attributed to the enhanced electron transfer kinetics and large electroactive surface area of the aligned CNTs. The electrode was successfully applied in differential electrolytic potentiometry (DEP) and zero-current potentiometry for the determination of ascorbic acid and ciprofloxacin in pharmaceutical and food samples using sequential injection analysis (SIA) and normal titrations. Parameters such as polarization mode, current density, square-wave period, and reagent flow rate were optimized. The sensor achieved a wide linear range: 0.06–0.85 mmol/L for ascorbic acid and 60–1000 µmol/L for ciprofloxacin, with results comparable to those from traditional Pt electrodes. The CNT/Ag electrode holds promise for further functionalization, offering versatility for diverse analytical applications. Overall, the integration of direct-grown CNTs with the DEP-SIA technique demonstrates a significant advancement in electrode design for sensitive, selective, and durable electrochemical sensing. Figure 1