This work reports the determination of 5 neonicotinoid pesticides (Clothianidin, Imidacloprid, Thiamethoxam, Nitenpyram and Dinotefuran) in water samples by cathodic differential pulse (DP) voltammetry at screen‐printed disposable sensors featuring a sputtered bismuth thick‐film working electrode, a Ag reference electrode and a carbon counter electrode. The performance of the bismuth thick‐film electrodes was compared to that of a home‐made bismuth thin‐film electrode and a bismuth‐bulk electrode. The electrodes were further characterized by electrochemical and optical techniques. The effect of the pH of the supporting electrolyte on the DP reduction currents of the 5 pesticides was studied. The limits of quantification (LOQs) in 4 water matrices (distilled water, tap water, mineral water and surface water) were in the range 0.76 to 2.10 mg L−1 but severe matrix effects were observed in the analysis of mineral and, especially, surface water samples. Using a solid‐phase extraction (SPE) procedure using Lichrolut EN cartridges and elution with methanol, the matrix effects were substantially reduced and the LOQs were in the range 9 to 17 µg L−1. The recoveries of surface water samples spiked with the 5 target neonicotinoids at two concentration levels (20 and 50 µg L−1) were in the range 89 to 109 % and the % relative standard deviations ranged from 4.3 to 7.2 %.
This work reports the application of screen‐printed electrodes bulk‐modified with bismuth precursors to the voltammetric determination of 2‐nitrophenol (2‐NP), 4‐nitrophenol (4‐NP) and 2,4‐dinitrophenol (2,4‐DNP) in water samples. A bismuth film was formed at the electrode surface via in situ reduction of the precursor compound contained in the electrode matrix by cathodic polarization at −1.20 V. The formation of bismuth layer at the precursor‐modified electrodes was assessed by cyclic voltammetric (CV) at different pH values and by optical techniques. The target nitrophenols were voltammetrically determined by recording their reduction peaks in the differential pulse (DP) mode. The composition and content of the precursor compounds in the printed ink and the effect of the pH of the supporting electrolyte on the DP reduction currents of the 3 target nitrophenols were studied. The limits of quantification (LOQs) in three water matrices (distilled water, tap water and surface water) were in the range 1.1–2.2 µmol L−1. Using a simple solid‐phase extraction (SPE) procedure with Lichrolut EN cartridges and elution with methanol, a preconcentration factor of 100 was achieved; the LOQs were 0.021, 0.027 and 0.025 µmol L−1 for 2‐NP, 4‐NP and 2,4‐DNP, respectively. The recoveries of samples spiked with the 3 target nitrophenols at two concentration levels (0.04 and 0.1 µmol L−1) were always >87 %.
This work reports the development of low-cost graphene-based screen-printed sensors using a "green" fabrication procedure. Three-electrode sensors featuring carbon working and counter electrodes and a Ag reference electrode were fabricated by screen-printing on flexible polymer film. Graphene suspension was prepared following a simple, fast and environment-friendly method of solvent exfoliation of graphite in N-methyl pyrrolidone (NMP). Graphene was further dispersed in Nafion and the solution was used to drop-coat the working electrode of the sensor. The modified electrode was characterized using Raman spectroscopy, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The graphene/Nafion modified sensors were used to determine caffeine by anodic adsorptive stripping voltammetry. The procedure consists of a short adsorptive preconcentration step of caffeine on the graphene working electrode followed by an anodic voltammetric scan in the differential pulse (DP) mode. The oxidation current of caffeine is related to its concentration in the sample. High sensitivity was achieved due to the preconcentration step of the target compound on the working electrode. The limit of detection (LOD) for caffeine was 0.021 μmol L -1 and the % relative standard deviation (n=8) was 2.0 %. The sensors were applied to the determination of caffeine in coffee and beverage samples.
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