Electrochemical determination of fenitrothion pesticide based on ultrathin manganese oxide nanowires/molybdenum titanium carbide MXene ionic nanocomposite and molecularly imprinting polymer.

A novel molecularly imprinted electrochemical sensor is presented based on one-dimensional ultrathin manganese oxide nanowires/two-dimensional molybdenum titanium carbide MXene (MnO2NWs@Mo2TiC2 MXene) for fenitrothion (FEN) determination. After the synthesis of MnO2NWs@Mo2TiC2 MXene ionic nanocomposite was successfully completed with a facile hydrothermal and the pillaring methods, a new type molecular imprinted electrochemical sensor based on MnO2NWs@Mo2TiC2 MXene was constructed with cyclic voltammetry (CV) polymerization including pyrrole monomer and FEN target molecule. After the characterization studies including spectroscopic, electrochemical and microscopic methods, the analytical applications of the prepared sensor were performed. A linearity of 1.0×10-9-2.0×10-8 mol L-1 was obtained and the values of the quantification limit (LOQ) and the detection limit (LOD) were 1.0×10-9 mol L-1 and 3.0×10-10 mol L-1, respectively. The studies of selectivity, stability and reproducibility of the constructed sensor based on MnO2NWs@Mo2TiC2 nanocomposite and molecularly imprinting polymer (MIP) were carried out in detail. Finally, the developed sensor was applied to white flour samples with the values close to 100%.

Highly conductive Ti3C2 MXene-supported CoAl-layered double hydroxide nanosheets for ultrasensitive electrochemical detection of organophosphate pesticide fenitrothion.

A novel electrochemical method is presented for ultrasensitive detection of the organophosphate pesticide (OPP) fenitrothion by using Ti3C2 MXene/CoAl-LDH nanocomposite as the electrode modifier. The Ti3C2 MXene/CoAl-LDH nanocomposite is synthesized by growing CoAl-LDH in situ on MXene nanosheets. The combination of two ultrathin 2D materials provides more active sites, larger specific surface area, superior adsorption properties, and better electrical conductivity, which leads to rapid electron-transfer and mass-transfer between the substrate electrode and analytes when it is acted as the electrochemical sensing material. In addition, through the chelation of phosphate groups with the Ti defect sites enriched in MXene, OPP is adsorbed on the electrode. Consequently, the corresponding modified electrode gives rise to a wide linear response range of 0.03 ~ 120 µmol/L for the differential pulse voltammetry detection of fenitrothion with a low detection limit of 5.8 nmol/L (3σ). The method offers good repeatability, stability, selectivity, and practicability for real samples. This strategy provides a reference platform for the electrochemical monitoring of trace OPPs residue by using MXene/LDH-based nanocomposites.

Acetylcholinesterase Inhibition in Rats and Humans Following Acute Fenitrothion Exposure Predicted by Physiologically Based Kinetic Modeling-Facilitated Quantitative In Vitro to In Vivo Extrapolation.

Worldwide use of organophosphate pesticides as agricultural chemicals aims to maintain a stable food supply, while their toxicity remains a major public health concern. A common mechanism of acute neurotoxicity following organophosphate pesticide exposure is the inhibition of acetylcholinesterase (AChE). To support Next Generation Risk Assessment for public health upon acute neurotoxicity induced by organophosphate pesticides, physiologically based kinetic (PBK) modeling-facilitated quantitative in vitro to in vivo extrapolation (QIVIVE) approach was employed in this study, with fenitrothion (FNT) as an exemplary organophosphate pesticide. Rat and human PBK models were parametrized with data derived from in silico predictions and in vitro incubations. Then, PBK model-based QIVIVE was performed to convert species-specific concentration-dependent AChE inhibition obtained from in vitro blood assays to corresponding in vivo dose-response curves, from which points of departure (PODs) were derived. The obtained values for rats and humans were comparable with reported no-observed-adverse-effect levels (NOAELs). Humans were found to be more susceptible than rats toward erythrocyte AChE inhibition induced by acute FNT exposure due to interspecies differences in toxicokinetics and toxicodynamics. The described approach adequately predicts toxicokinetics and acute toxicity of FNT, providing a proof-of-principle for applying this approach in a 3R-based chemical risk assessment paradigm.

Preparation of magnetic molecularly imprinted polymer based on multiwalled carbon nanotubes for selective dispersive micro-solid phase extraction of fenitrothion followed by ion mobility spectrometry analysis.

A novel molecularly imprinted polymer based on magnetic multiwalled carbon nanotubes was fabricated and applied for selective dispersive micro-solid phase extraction of fenitrothion prior its determination by ion mobility spectrometry. The composite was synthesized using magnetic multiwalled carbon nanotubes as the support. Methacrylic acid was used as the functional monomer, fenitrothion as the template, ethylene glycol dimethacrylate as the cross-linker, and 2,2-azoisobutyronitrile as the initiator. The resultant polymer was characterized by FTIR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, Brunauer-Emmet-Teller analysis, thermogravimetric analysis, and vibrating sample magnetometer techniques. Experimental factors affecting the extraction efficiency such as pH and amount of sorbent were evaluated. Under optimum experimental conditions, the developed method displayed the linear range of 5-220 µg/L with a detection limit of 1.3 µg/L. The intra- and interday relative standard deviations for determination of fenitrothion were 3.6 and 4.7% (n = 6), respectively. Ultimately, the proposed method was used to monitor trace amounts of fenitrothion in fruits, vegetables, and water samples.

An Electrochemical Sensor Based on Electropolymerization of ß-Cyclodextrin on Glassy Carbon Electrode for the Determination of Fenitrothion.

An electrochemical sensor enabled by electropolymerization (EP) of ß-cyclodextrin on glassy carbon electrode (ß-CDP/GCE) is built for the determination of fenitrothion (FNT). The effects of the EP cycles, pH value, and enrichment time on the electrochemical response of FNT were studied. With the optimum conditions, good linear relationships between the current of the reduction peak of the nitroso derivative of FNT and the concentration are obtained in the range of 10-150 and 150-4000 ng/mL, with a detection limit of 6 ng/mL (S/N = 3). ß-CDP/GCE also exhibits a satisfactory applicability in cabbage and tap water, with recovery values between 98.43% and 112%. These outstanding results suggest that ß-CDP/GCE could be a new effective alternative for the determination of FNT in real samples.

Quercetin ameliorates the hepatic apoptosis of foetal rats induced by in utero exposure to fenitrothion via the transcriptional regulation of paraoxonase-1 and apoptosis-related genes.

BACKGROUND & PURPOSE: Exposure to organophosphorus during different phases of pregnancy induces many adverse impacts on the developing foetuses due to their immature detoxification system. We have estimated the potential amelioration role of quercetin against hepatic injury-induced apoptosis in rat foetuses following gestational exposure to fenitrothion and probable involvement of paraoxonase-1. METHODS: Forty pregnant rats were allocated into four groups; the first one kept as control, the second intubated with quercetin (100 mg/kg), the third orally administrated fenitrothion (4.62 mg/kg) and the last group received quercetin two hours before fenitrothion intoxication. RESULTS: Fenitrothion significantly elevated the foetal hepatic levels of thiobarbituric acid reactive substances, protein carbonyl, and nitric oxide, but it reduced the enzymatic activities of glutathione-S-transferase, superoxide dismutase, catalase, and acetylcholinesterase. Furthermore, fenitrothion provoked many histopathological changes in the foetal liver and markedly up-regulated the mRNA gene expression of p53, caspase-9 along with elevation in the immunoreactivity of Bax and caspase-3, but it down-regulated the expression level of paraoxonase-1. Remarkably, quercetin co-treatment successfully ameliorated the hepatic oxidative injury and apoptosis prompted by fenitrothion. CONCLUSIONS: Dietary supplements with quercetin can be used to reduce the risk from organophosphorus exposure probably through paraoxonase-1 up-regulation and enhancement of the cellular antioxidant system.

Facile synthesis of petal-like VS2 anchored onto graphene nanosheets for the rapid sensing of toxic pesticide in polluted water.

Fenitrothion (FT) is a toxic phosphorothioate insecticide that can easily contaminate aquatic environments, leading to a detrimental effect on the aquatic species and harmful endocrine disrupter effects on human health. Therefore, it is vital to develop a reliable methodology for the accurate and precise real-time sensing of carcinogenic FT in water samples at trace concentration to ensure environmental safety. We aim to fabricate the low-cost VS2-attached reduced graphene oxide (RGO) sheets via a simple hydrothermal approach. It was further applied for the rapid and accurate sensing of toxic FT. The VS2/RGO-composite delivers a more favorable microenvironment for the rapid electrocatalytic sensing performance towards toxic FT reduction than the VS2 and RGO modified electrodes. The electron transfer rate constant (ks) and the saturating absorption capacity (Γ) value of FT was evaluated to be 1.52 s-1 and 2.18 × 10-10 mol cm-2, respectively. The constructed sensor exhibits a wide linear relationship after amperometry between the cathodic current densities and the concentrations of FT in the range of 5-90 nM and high sensitivity (5.569 µA nM-1 cm-2); moreover, the detection limit was 0.07 nM (S/N = 3). The fabricated sensor has excellent anti-interference ability and reproducibility for the direct sensing of FT in river water, seawater, and lake water samples with acceptable recoveries. It is a promising sensing device for in-situ quantification of FT in agricultural products and ecological systems.

A method for topical dosing of invertebrates with pesticide for use in feeding experiments.

The ability to produce large numbers of pesticide-exposed insects (e.g. crickets) is important for feeding studies into the effects of pesticides on key predatory species. House crickets (Acheta domesticus L. 1758) were submersed in serial dilutions of the pesticides, fenitrothion and fipronil, used for the control of locusts in Australia, and then rapidly frozen for residue analysis. Good correlations were found between increasing concentrations of serial pesticide dilutions and the resultant residual concentrations of the parent compounds in crickets, with R2 values of 0.949 (fenitrothion) and 0.946 (fipronil). R2 values for the much less abundant fipronil metabolites were lower 0.858 (sulfone), 0.368 (desulfinyl) and 0.785 (sulfide). This method enables insecticide exposure mimicking the field conditions to be assessed, and can be done immediately prior to an experiment. This ensures locusts remain alive when introduced to the feeding chambers, and enables multiple prey items to be dosed with a known pesticide burden.

The ameliorative effect of curcumin on hepatic CYP1A1 and CYP1A2 genes dysregulation and hepatorenal damage induced by fenitrothion oral intoxication in male rats.

This research aimed to assess curcumin (CUR) effects on fenitrothion (FNT), a broad-spectrum organophosphate insecticide, -induced hepatorenal damage. Thirty adult male Wistar rats were allocated at random to five equal groups orally administered distilled water containing 1% carboxyl methylcellulose, corn oil (1 mL/rat), CUR (100 mg/kg b.wt.), FNT (5 mg/kg b.wt.), or CUR + FNT. CUR and FNT were dosed three times a week for two months. At the end of this trial, blood and tissue samples (liver and kidney) were subjected to molecular, biochemical, and histopathological assessments. The results revealed that CUR significantly diminished the FNT-induced up-regulation of hepatic CYP1A1 and CYP1A2 transcriptional levels. Moreover, CUR significantly suppressed the increment of the serum levels of hepatic alanine aminotransferase, gamma-glutamyl transferase, and kidney damage indicators (urea and creatinine) in FNT-intoxicated rats. Furthermore, in the hepatic and renal tissues, CUR remarkably restored the FNT-associated depletion of the antioxidant enzymes (glutathione peroxidase, glutathione reductase, glutathione S transferase, catalase, and superoxide dismutase). In addition, CUR notably reduced the FNT-induced increment in malondialdehyde content in the hepatic and renal tissues. Besides, the pathological aberrations in liver and kidney tissues resulting from FNT exposure were significantly abolished in FNT + CUR treated rats. Overall, CUR could be an effective ameliorative agent against negative pesticide impacts like FNT.

Linseed ameliorates renal apoptosis in rat fetuses induced by single or combined exposure to diesel nanoparticles or fenitrothion by inhibiting transcriptional activation of p21/p53 and caspase-3/9 through pro-oxidant stimulus.

Gestational exposure to environmental pollutants can induce oxidative injury and apoptosis since the fetal organs are sensitively vulnerable to these chemicals. In this work, we have investigated the renal anti-apoptotic efficiency of linseed (LS) against the oxidative stress-mediated upregulation of the fetal apoptosis-related genes following the prenatal intoxication with diesel nanoparticles (DNPs) and/or fenitrothion (FNT). A fifty-six timed-pregnant rats were equally divided to eight groups; control, LS (20% in diet), DNPs (0.5 mg/kg by intratracheal inoculation), FNT (3.76 mg/kg by gavage), DNPs+FNT, LS + DNPs, LS + FNT, and LS + DNPs+FNT. The transmission electron microscope analysis revealed the spherical shape of diesel particles with a homogeneous nanosized range (20-92.3 nm) and the crystallinity was confirmed by electron diffraction microscopy. Administration of DNPs and/or FNT significantly increased fetal renal malondialdehyde, nitric oxide, and glutathione reductase as compared with the control group. However, they declined the level of glutathione together with the activities of glutathione peroxidase, glutathione-S-transferase, superoxide dismutase, and catalase. Furthermore, DNPs and/or FNT elicited many histopathological changes in fetal renal cells, markedly up-regulated apoptosis-related gene expressions (p53, p21 caspase-3, and caspase-9), and evoked DNA breaks as detected by comet assay. Interestingly, LS supplementation significantly ameliorated the disturbances in oxidant/antioxidant biomarkers, downregulated the apoptosis gene expressions, and alleviated DNA damage alongside renal cell architecture. These findings reveal that the antioxidant and anti-apoptotic characteristics of LS are acceptable defender pointers for the renal injury especially during gestational exposure to DNPs and/or FNT.

Novel DNA Aptameric Sensors to Detect the Toxic Insecticide Fenitrothion.

Fenitrothion is an insecticide belonging to the organophosphate family of pesticides that is widely used around the world in agriculture and living environments. Today, it is one of the most hazardous chemicals that causes severe environmental pollution. However, detection of fenitrothion residues in the environment is considered a significant challenge due to the small molecule nature of the insecticide and lack of molecular recognition elements that can detect it with high specificity. We performed in vitro selection experiments using the SELEX process to isolate the DNA aptamers that can bind to fenitrothion. We found that newly discovered DNA aptamers have a strong ability to distinguish fenitrothion from other organophosphate insecticides (non-specific targets). Furthermore, we identified a fenitrothion-specific aptamer; FenA2, that can interact with Thioflavin T (ThT) to produce a label-free detection mode with a Kd of 33.57 nM (9.30 ppb) and LOD of 14 nM (3.88 ppb). Additionally, the FenA2 aptamer exhibited very low cross-reactivity with non-specific targets. This is the first report showing an aptamer sensor with a G4-quadruplex-like structure to detect fenitrothion. Moreover, these aptamers have the potential to be further developed into analytical tools for real-time detection of fenitrothion from a wide range of samples.

Current Status and Future Prognosis of Malaria Vector Control Pesticide Ecotoxicology and Xenopus sp.

Anurans from the genus Xenopus have long been used as standard testing organisms and occur naturally in tropical and sub-tropical areas where malaria vector control pesticides are actively used. However, literature on the toxic effects of these pesticides is limited. This review analyses the available data pertaining to both Xenopus and the pesticides used for malaria vector control in order to determine the pesticides that have the greatest potential to influence amphibian health while also identifying gaps in literature that need to be addressed. Amphibian diversity has shown the fastest decline of any group, yet there are still voids in our understanding of how this is happening. The lack of basic toxicity data on amphibians with regard to pesticides is an issue that needs to be addressed in order to improve effectiveness of amphibian conservation strategies. Meta-analyses performed in this review show that, at current usage, with the available acute toxicity literature, the pyrethroid pesticide group could hold the highest potential to cause acute toxicity to Xenopus sp. in relation to the other MVCPs discussed, but the lack of data cripples the efficacy with which meta-analyses can be performed and conclusions made from such analyses. Several studies have shown that DDT accumulates in Xenopus sp. from malaria vector control areas, but accumulation of other MVCPs in frogs is still largely unknown. Through this review we hope to encourage future research into the field of amphibian ecotoxicology and to promote the use of the Xenopus standard model in order to build comprehensive datasets that may be used in amphibian conservation.

Fabric phase sorptive extraction followed by HPLC-PDA detection for the monitoring of pirimicarb and fenitrothion pesticide residues.

A sensitive and readily deployable analytical method has been reported for the simultaneous analysis of pirimicarb (PRM) and fenitrothion (FEN) pesticide residues in environmental water samples using fabric phase sorptive extraction (FPSE) followed by high-performance liquid chromatography combined with photodiode array (HPLC-PDA) detector. Both pesticides were successfully determined with a Luna omega C18 column under isocratic elution mode by means of acetonitrile and phosphate buffer (pH 3.0) as the mobile phase. The quantitative data for PRM and FEN were obtained at their maximum wavelengths of 310 nm and 268 nm, respectively. The calibration plots were linear in the range 10.00-750.00 ng mL-1 and 10.00-900.00 ng mL-1 with correlation coefficient of 0.9984 and 0.9992 for PRM and FEN, respectively. Major FPSE experimental variables were investigated in detail, such as contact time with the FPSE membrane, pH and electrolyte concentration, and the volume and type of desorption solvent. Under the optimized conditions, the developed method showed satisfactory reproducibility with relative standard deviations less than 2.5% and low limits of detection of 2.98 and 3.02 ng mL-1 for PRM and FEN, respectively. The combined procedure allows for enhancement factors ranging from 88 to 113, with pre-concentration values of 125 for both analytes. The chromatographic resolutions were approx. 12 for FEN (retention factor of 3.52) and PRM (retention factor of 6.09), respectively, with a selectivity factor of 1.73. Finally, the validated method was successfully applied to real environmental water samples for the determination of these pesticides. Graphical abstract.

Photodegradation of Organophosphorus Pesticides in Honey Medium by Solar Light Irradiation.

In this study, the photodegradation of organophosphorus (OPs) pesticides in the honey medium was evaluated under sunlight irradiation. Some of the 22 samples collected at different sites contained OPs pesticides (Methyl parathion, Coumaphos and Fenitrothion) with an average of 8 ng/g. Moreover, three samples were found with pesticide residue levels exceeding the maximum residue limits (MRL ≥ 50 ng/g) imposed by the standard water (WHO). Gas chromatography (GC) combined with a tritium electron capture detector system was used for the analysis of OPs pesticides in honey. Total degradation of the Methyl parathion was obtained in less than 60 min of irradiation. Moreover, the elimination of the other OPs found in the samples was also effective with a rate of 85% for Coumaphos and Fenitrothion after 50 min of sunlight irradiation. The kinetics of the photodegradation reaction of all OPs pesticides studied followed a pseudo-first order model.

Protective effect of N-acetylcysteine on fenitrothion-induced toxicity: The antioxidant status and metabolizing enzymes expression in rats.

The existence of fenitrothion (FNT) in the soil, water, and food products has harmful effects on non-target organisms. Therefore, this study was conducted to evaluate the hepatotoxic, nephrotoxic and neurotoxic effects of FNT and the possible ameliorative effect of N-acetylcysteine (NAC), a precursor of intracellular GSH, on FNT-induced toxicity. For this purpose, thirty-two adult male albino rats were allocated into control group and groups treated with NAC (200 mg/kg), FNT (10 mg/kg) and FNT + NAC via gastric tube daily for 28 days. FNT intoxication significantly reduced food intake, water intake, body weight, and body weight gain and altered the expression of phase I and phase II xenobiotic-metabolizing enzymes-cytochrome P450 (CYP1A1) and glutathione S-transferase (GSTA4-4). In hepatic, renal and brain tissues, FNT induced oxidative stress, hepatopathy, nephropathy, and encephalopathy, and significantly increased pro-inflammatory cytokines. Furthermore, FNT exposure significantly elevated the level of hepatic and renal injury biomarkers and significantly inhibited the brain acetylcholinesterase activity. Co-administration of NAC with FNT modulated most of these altered biochemical, oxidative and inflammatory markers and restored the xenobiotic-metabolizing enzymes expression and histological structures. Our study indicated the involvement of oxidative damage, inflammation, and alteration of xenobiotic-metabolizing enzymes expression in FNT-induced toxicity and revealed that they were significantly improved by NAC co-treatment. These findings suggest that NAC administration might protect against FNT-induced toxicity in non-target organisms, including humans.

Modulatory effect of Turnera diffusa against testicular toxicity induced by fenitrothion and/or hexavalent chromium in rats.

Oxidative stress and increased production of reactive oxygen species have been implicated in pesticides and heavy metals toxicity. The objective of this study was to investigate the efficacy of Turnera diffusa Willd (damiana) on counteracting fenitrothion (FNT) and/or potassium dichromate (CrVI)-induced testicular toxicity and oxidative injury in rats. FNT and/or CrVI intoxicated animals revealed a significant increase in thiobarbituric acid reactive substances and hydrogen peroxide levels. While, reduced glutathione and protein content, as well as antioxidant enzymes, phosphatases, and aminotransferases activities, were significantly decreased. In addition, significant changes in testosterone and follicle-stimulating hormone levels were detected. Furthermore, histological and immunohistochemical alterations were observed in rat testes and this supported the observed biochemical changes. On the other hand, rats treated with damiana alone decreased lipid peroxidation and increased most of the examined parameters. Moreover, damiana pretreatment to FNT and/or CrVI-intoxicated rats showed significant improvement in lipid peroxidation, enzyme activities, and hormones as compared with their respective treated groups. Conclusively, rats treated with both FNT and/or CrVI showed pronounced hazardous effect especially in their combination group in addition, Turnera diffusa had a potential protective role against FNT and/or CrVI induced testicular toxicity.

Surface plasmon resonance based fiber-optic nanosensor for the pesticide fenitrothion utilizing Ta2O5 nanostructures sequestered onto a reduced graphene oxide matrix.

A surface plasmon resonance study was carried out for the identification and determination of the organophosphate pesticide fenitrothion via an optical fiber sensor. A thin layer of silver was deposited on the unclad core of silica optical fiber for plasmon generation. This was followed by the deposition of a sensing surface comprising a layer of tantalum(V) oxide nanoparticles sequestered in a nano-scaled matrix of reduced graphene oxide. The sensing mechanism is due to the interaction of fenitrothion with the silver film which leads to a change in refractive index.. Characterized by a wavelength interrogation scheme, the fiber-optic sensor exhibited a red shift equalling 56 nm corresponding to fenitrothion concentration in the range 0.25-4 µM including the blank solution. The spectral sensitivity is 24 nm µM-1, the limit of detection is 38 nM, and the response time is as short as 23 s. The sensor is selective, repeatable and works at ambient temperature. Graphical abstractSchematic representation of the sensing mechanism of an SPR based fiber-optic fenitrothion sensor utilizing modification in refractive index of sensing surface comprising of tantalum(V) oxide (Ta2O5) nanoparticles embedded in reduced graphene oxide (rGO) caused by interaction with fenitrothion entities.

Analytical Methodology for Trace Determination of Propoxur and Fenitrothion Pesticide Residues by Decanoic Acid Modified Magnetic Nanoparticles.

A sensitive, rapid, reliable, and easily applicable method based on magnetic solid phase extraction (MSPE) combined with HPLC-PDA was developed for monitoring propoxur (PRO) and fenitrothion (FEN) pesticides in environmental water samples. The effect of major experimental variables on the extraction efficiency of both the pesticides was investigated and optimized systematically. For this purpose, a new magnetic material containing decanoic acid on the surface of particles was synthesized and characterized by XRD, FT-IR, SEM, EDX, and TGA analysis in detail. The simultaneous determination of pesticide molecules was carried out by using a Luna Omega C18 column, isocratic elution of acetonitrile (ACN): Water (70:30 v/v) with a flow rate of 1.2 mL min-1. After MSPE, the linear range for pesticide molecules (r2 > 0.9982) was obtained in the range of 5-800 and 10-800 ng mL-1, respectively. The limit of detections (LOD) are 1.43 and 4.71 ng mL-1 for PRO and FEN, respectively while RSDs % are below 3.5%. The applicability of the proposed method in four different environmental samples were also investigated using a standard addition-recovery procedure. Average recoveries at two spiking levels were over the range of 91.3-102.5% with RSD < 5.0% (n = 3). The obtained results show that decanoic acid grafted magnetic particles in MSPE combined with HPLC-PDA is a fast and simple method for the determination of PRO and FEN in environmental water samples.

Electrochemical enzymatic fenitrothion sensor based on a tyrosinase/poly(2-hydroxybenzamide)-modified graphite electrode.

This paper reports the electrosynthesis and characterisation of a polymeric film derived from 2-hydroxybenzamide over a graphite electrode and its application as an enzymatic biosensor for the determination and quantification of the pesticide fenitrothion. The material was analysed by scanning electron microscopy and its electrochemical properties characterised by cyclic voltammetry and electrochemical impedance spectroscopy. The enzyme tyrosinase was immobilised over the modified electrode by the drop and dry technique. Catechol was determined by direct reduction of biocatalytically formed o-quinone by employing the flow injection analysis technique. The analytical characteristics of the proposed sensor were optimised as follows: phosphate buffer 0.050 M at pH 6.5, flow rate 5.0 mL min-1, sample injection volume 150 µL, catechol concentration 1.0 mM and maximum inhibition time by fenitrothion of 6 min. The biosensors showed a linear response to pesticide concentration from 0.018 to 3.60 µM. The limit of detection and limit of quantification were calculated as 4.70 nM and 15.9 nM (RSD < 2.7%), respectively. The intra- and inter-electrode RSDs were 3.35% (n = 15) and 8.70% (n = 7), respectively. In addition, water samples spiked with the pesticide showed an average recovery of 97.6% (±1.53).

Temperature-controlled liquid-liquid microextraction combined with high-performance liquid chromatography for the simultaneous determination of diazinon and fenitrothion in water and fruit juice samples.

A simple, environmentally benign, and rapid method based on temperature-controlled liquid-liquid microextraction using a deep eutectic solvent was developed for the simultaneous extraction/preconcentration of diazinon and fenitrothion. The method involved the addition of deep eutectic solvent to the aqueous sample followed by heating the mixture in a 75°C water bath until the solvent was completely dissolved in the aqueous phase. Then, the resultant solution was cooled in an ice bath and a cloudy solution was formed. Afterward, the mixture was centrifuged and the enriched deep eutectic solvent phase was analyzed by high-performance liquid chromatography with ultraviolet detection for quantification of the analytes. The factors affecting the extraction efficiency were optimized. Under the optimized extraction conditions, the limits of detection for diazinon and fenitrothion were 0.3 and 0.15 µg/L, respectively. The calibration curves for diazinon and fenitrothion exhibited linearity in the concentration range of 1-100 and 0.5-100 µg/L, respectively. The relative standard deviations for five replicate measurements at 10.0 µg/L level of analytes were less than 2.8 and 4.5% for intra- and interday assays, respectively. The developed method was successfully applied to the determination of diazinon and fenitrothion in water and fruit juice samples.