A simple, sensitive and time-saving differential-pulse adsorptive stripping voltammetric (DPAdSV) procedure using a screen-printed carbon electrode modified with carboxyl functionalized multiwalled carbon nanotubes (SPCE/MWCNTs-COOH) for the determination of diclofenac (DF) is presented. The sensor was characterized using optical profilometry, SEM, and cyclic voltammetry (CV). The use of carboxyl functionalized MWCNTs as a SPCE modifier improved the electron transfer process and the active surface area of sensor. Under optimum conditions, very sensitive results were obtained with a linear range of 0.1-10.0 nmol L −1 and a limit of detection value of 0.028 nmol L −1 . The SPCE/MWCNTs-COOH also exhibited satisfactory repeatability, reproducibility, and selectivity towards potential interferences. Moreover, for the first time, the electrochemical sensor allows determining the real concentrations of DF in environmental water samples without sample pretreatment steps.Keywords: screen-printed carbon electrode modified with carboxyl functionalized multiwalled carbon nanotubes; diclofenac; differential-pulse adsorptive stripping voltammetry; environmental water samples; HPLC with photo-diode array detection Materials 2020, 13, 781 2 of 15 to ground and surface water, causing their pollution. Low water temperatures and short days hinder the process of photolysis and the biodegradation of pharmaceutical preparations, which can cause adverse and unpredictable effects in the ecosystem. The main sources of pollution are factories and production plants, as well as hospitals, health centers, and practically every household. DF is one of the most commonly found ingredients in water, and its concentration is from 3.7 × 10 −11 to 1.4 × 10 −8 mol L −1 [2,3].Although the likelihood of any form of short-term human health risk after DF release into the environment is low, a study links the catastrophic decline of Gyps vulture populations across the Indian subcontinent to DF [4,5]. Generally, NSAIDs such as DF and ibuprofen, for example, have Log Kow values greater than three and may have the capacity to bioaccumulate in the tissues of organisms [6]. DF exhibits acute hepatotoxicity, causes changes in kidneys and gills in rainbow trout (O. mykiss) and exhibits acute toxicity to phytoplankton and zooplankton. Moreover, the possibility of synergetic effects with other pharmaceuticals or chemicals in the aquatic environment increases the environmental risk as well [7].There are many methods in the literature that allow for the determination of DF at various concentration levels. The most popular methods are spectrophotometry (determined DF concentrations: 6.8 × 10 −7 -8.4 × 10 −2 mol L −1 ), spectrofluorimetry (determined DF concentrations: 4.2 × 10 −7 -1.7 × 10 −4 mol L −1 ), calorimetry (determined DF concentrations: 4.6 × 10 −6 -2.7 × 10 −4 mol L −1 ), high-performance thin-layer chromatography (determined DF concentrations: 6.8 × 10 −7 -2.7 × 10 −6 mol L −1 ), and HPLC (determined DF concentrations: 1.7 × 10 −8 -1.4 × 10 −5 mol L −1 )...
The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10−9 to 5.0×10−8 mol L−1 (r=0.9991) and 1.0×10−7–2.0×10−6 mol L−1 ( r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10−10 mol L−1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about −68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples.
A commercially available screen-printed carbon electrode coated with carbon nanofibers (SPCE/CNFs) and differentialpulse adsorptive stripping voltammetry (DPAdSV) were used to determination of caffeine. The process of electrochemical oxidation of caffeine in 0.1 mol L −1 sulfuric acid at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV). The effect of the supporting electrolyte type, pH and concentration, time and potential of accumulation, amplitude and scan rate were studied to select the optimum experimental conditions. Under the optimized conditions, the well-defined caffeine peak was observed at 1.25 V (vs. screen-printed silver reference electrode) in 0.1 mol L −1 sulfuric acid. The caffeine was accumulated at − 0.8 V for 60 s. The oxidation peak current was proportional to concentration of caffeine from 2.0 × 10 −7 to 1.0 × 10 −6 mol L −1 with detection limit of 5.6 × 10 −8 mol L −1. The presented method has been successfully applied for the determination of caffeine in beverage samples. Keywords Integrated three-electrode screen-printed sensor with carbon/carbon nanofibers working electrode • Adsorptioncontrolled process • Diffusion-controlled process • Voltammetric determination of caffeine • Beverage samples This article belongs to S.I. ISSHAC10, but it reach the press at the time the special issue was published.
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