Graphene derivatives-based electrodes for the electrochemical determination of carbamate pesticides in food products: A review

Graphene (GR) composites have great potential for the determination of carbamates pesticides (CPs) by electrochemical methods. Since the beginning of the 20th century, GR has shown remarkable promise as electrode material for various sensors. The contamination of food products with harmful CPs is a major problem as they do not always damage human health immediately, but can be harmful after prolonged exposure. A range of advantages can be gained from their electrochemical determination, such as high sensitivity, reasonably selectivity, rapid detection, low limit of detection, and easy electrode fabrication. Furthermore, these electrochemical techniques are robust, reproducible, user-friendly, and conform to both "green" and "white" analytical chemistry. This review is focused on results published in the last ten years in the field of electrochemical determination of CPs in food products using GR and its derivatives.

Activated Porous Carbon Supported Pd and ZnO Nanocatalysts for Trace Sensing of Carbaryl Pesticide in Water and Food Products

Nanomaterials-based sensors are a dire need for credible and accurate determination of pesticides in water and food samples as a monitoring tool. Herein, electrocatalysts of Pd and ZnO NPs supported...

Highly Selective Electrochemical Sensor Based on Gadolinium Sulfide Rod-Embedded RGO for the Sensing of Carbofuran

Nowadays, a lot of pesticides have been used in the agriculture field due to the global demand for food production. Carbofuran (CF) is the most commonly used carbamate compound that is responsible for the highest toxicity to humans compared to any other pesticide used in agricultural settings. Thus, rapid, portable, and low-cost sensors are needed for the detection of CF in the environment and food samples. Herein, we have successfully developed an electrochemical sensor using a glassy carbon electrode (GCE) modified with gadolinium sulfide (Gd₂S₃) and reduced graphene oxide (RGO) composite for the detection of carbofuran (CF). A novel Gd₂S₃/RGO composite was prepared by the facile hydrothermal route and confirmed by morphological and structural analyses such as field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX), powder X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and also the formation mechanism of Gd₂S₃/RGO composite was discussed. The desired electrical conductivity of Gd₂S₃ was enhanced by the RGO, which was estimated from the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Electrochemical studies demonstrated that the developed Gd₂S₃/RGO sensor was highly sensitive and selective to CF. In addition, the Gd₂S₃/RGO sensor exhibits a low detection limit (LOD) and the linear ranges were 0.0128 and 0.001-1381 μM, respectively, for CF detection under optimized experimental conditions. Moreover, we also investigated the practical applicability of the sensor for CF detection in the environment and food samples.

Temperature-Controllable Electrodes with a One-Parameter Calibration

Electrically heated electrodes have been applied for various chemical and biological sensors. However, previous electrically heated electrodes, including microwires and microdiscs, are usually small and often suffer from the requirement of frequent calibrations of the electrode surface temperature ( T_s) at different environment temperatures. Here, we fabricate a temperature-controllable disk electrode (TCDE) with a conventional size (3-5 mm in diameter). A one-parameter temperature calibration is proposed using a temperature transfer coefficient α and a structural model ( T_s = T_e + α ( T_h - T_e)) to estimate T_s ( T_h and T_e are the temperature of the heating element and environment, respectively). The value of α is unique for a TCDE and mainly dependent on the structure and materials of the electrodes and the solution in nature. Once α is experimentally determined, T_s can be calibrated and found to be applicable to wide fluctuations in room temperature (15.0-33.0 °C) with errors below 1.5% for three types of disk electrodes (gold, glassy carbon, and platinum). The required T_s can be obtained by just setting T_h without thermal characterization between the heating power and T_s. A simple relationship for exploring the dependence of α on the height ( H) and radius ( R) of the electrode materials and other constants ( a, b, c, and R₀), α = 1 - c - aH - b ( R - R₀)², is revealed by numerical simulations (COMSOL). The impact of the radii of both the insulating materials of the electrode and the electrochemical cells on T_s is also considered. The effect of the solution thermal conductivity on α is studied. TCDEs are expected to be used as a sensor platform with enhanced performance.

Promising post-consumer PET-derived activated carbon electrode material for non-enzymatic electrochemical determination of carbofuran hydrolysate

In this work, activated carbon (AC) materials, prepared from polyethylene terephthalate (PET) waste bottles were used as the sensing platform for the indirect detection of carbofuran. The morphology and surface properties of the PET-derived AC (PET-AC) were characterized by N₂ adsorption/desorption isotherm, X-ray diffraction (XRD), field-emission scanning/transmission electron microscopy (FE-SEM/TEM) and Raman spectroscopy. The electrochemical activity of the PET-AC modified glassy carbon electrode (GCE) (PET-AC/GCE) was measured by cyclic voltammetry and amperometry. The enhanced surface area and desirable porosities of PET-AC are attributed for the superior electrocatalytic activity on the detection of carbofuran phenol, where, the proposed sensor shows low detection limit (0.03 µM) and remarkable sensitivity (0.11 µA µM⁻¹ cm⁻²). The PET-AC/GCE holds high selectivity towards potentially interfering species. It also provides desirable stability, repeatability and reproducibility on detection of carbofuran phenol. Furthermore, the proposed sensor is utilized for the detection of carbofuran phenol in real sample applications. The above mentioned unique properties and desirable electrochemical performances suggest that the PET-derived AC is the most suitable carbonaceous materials for cost-effective and non-enzymatic electrochemical sensor.

Development of Micellar HPLC-UV Method for Determination of Pharmaceuticals in Water Samples

Method for extraction and determination of amoxicillin, caffeine, ciprofloxacin, norfloxacin, tetracycline, diclofenac, ibuprofen, nimesulide, levonorgestrel, and 17α-ethynylestradiol exploiting micellar liquid chromatography with PDA detector and solid-phase extraction was proposed. The usage of toxic solvents was low; the chromatographic separation of the medicaments was performed using a C18 column and mobile phases A and B containing 15.0% (v/v) ethanol, 3.0% (m/v) sodium dodecyl sulfate (SDS), and 0.02 mol·L^-1 phosphate at pHs 7.0 and 8.0, respectively. The method is simple, selective, and fast, and the analytes were separated in 23.0 min. For extraction, 1000 mL of sample containing 2.0% (v/v) ethanol and 0.002 mol·L^-1 citric acid at pH 2.50 was loaded through a 1000 mg of C18 cartridge. The analytes were eluted using 3.0 mL of ethanol, which were evaporated and redissolved in 0.5 mL of mobile phase. Concentration factors better than 1200, except amoxicillin (224), were obtained. The analytical curves were linear (R² better than 0.992); LOD and LOQ (n=10) presented values in the range of 0.019-0.247 and 0.058-0.752 mg·L^-1, respectively. Recoveries of 99% were obtained, and the results are in agreement with those obtained by the comparative methods.

Electrochemical sensor based on low silica X zeolite modified carbon paste for carbaryl determination

A new and simple approach for carbaryl determination in natural sample was proposed using Low Silica X (LSX) zeolite modified carbon paste electrode. LSX zeolite with a porous structure was incorporated into carbon paste electrode in the appropriate portion. The prepared electrode was then characterized using scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Various experimental parameters as the zeolite amounts, pH, accumulation time, and differential pulse voltammetric parameters were optimized. Under optimal conditions, a linear response was obtained in the range of 1-100 µM of carbaryl using differential pulse voltammetry with detection limit of 0.3 µM (S/N = 3). The sensors showed good selectivity, stability, and reproducibility and has been successfully applied for detection of carbaryl in tomato samples with good recoveries.

Online microchannel preconcentrator for carbofuran detection

A simple and rapid online microchannel preconcentrator coupled with an amperometric detection for the analysis of carbofuran using polyethylene glycol coated onto magnetic particle (PEG-magnetic particles) sorbents was developed. This simple-to-prepare microchannel preconcentrator used an external magnet to retain the PEG-magnetic particle sorbents inside the microchannel. Under optimum conditions, the system provided two linear ranges, from 0.01 to 10.0 mg L(-1) and from 10.0 to 130.0 mg L(-1) with a limit of detection of 8.7 ± 0.1 μg L(-1). The microchannel preconcentrator provided very good stability; it can be used for up to 326 consecutive injections of 5.0 mg L(-1) carbofuran with a relative standard deviation of less than 3%. The developed system provided a good microchannel-to-microchannel and a good electrode-to-electrode reproducibility (n = 6, %RSD < 1). It also provided an excellent selectivity when it was tested with two other carbamate pesticides, carbaryl and methomyl, with a 43 and 256 times higher detection sensitivity for carbofuran, respectively. The developed system was successfully applied to detect carbofuran in surface water samples obtained near vegetable plantation areas. The concentrations of carbofuran in these samples were found to be in the range of non-detectable to 0.047 ± 0.001 mg L(-1). The developed system is easy to operate and easy to couple with other analytical instruments and it could be easily adapted for the analysis of other polar organic contaminants.