Determination of diphenylamine residue in fruit samples using spectrofluorimetry and multivariate analysis

A disposable voltammetric sensor for the determination of diphenylamine using modified pencil graphite electrode

This study reports the electrochemical monitoring and sensing of diphenylamine (DPA), an anti-scald agent on a modified pencil graphite electrode (PGE). DPA is also a potentially toxic environmental pollutant. A polymer of tyrosine synthesized by electrochemical process was utilized for the determination of DPA in real samples. The electrodes were characterized using IR, SEM, EDAX, AFM and EIS analyses. As far as we know, this is first time reporting the utilization of modified PGE via green approach for the monitoring of DPA. A dynamic linear range of 1.00-117.11 µM with a lower detection limit (LOD) of 0.7050 µM was showed by this sensor for the electrochemical quantification of DPA. The electrochemical oxidation of DPA on the modified sensor followed a mixed adsorption -diffusion controlled kinetics. The sensor also showed good anti-interference property for the determination of DPA in real samples. Furthermore, the developed sensor was applied for the selective sensing of DPA from real apple extracts with good recovery. The real sample analysis was validated with standard spectrophotometric method.

La-doped NiWO4 coupled with reduced graphene oxide for effective electrochemical determination of diphenylamine

Diphenylamine (DPA) is a harmful pesticide widely used to control post-harvest scald of fruits. In this study, rapid and sensitive determination of DPA was realized by the development of an effective electrochemical sensor, which was fabricated by coupling La-doped NiWO4 nanoparticles (La/NiWO4) with reduced graphene oxide (rGO), and the obtained rGO/La/NiWO4 nanocomposite was modified on glassy carbon electrodes (GCEs). The morphologies, structures and compositions were well characterized, and the effects of La doping and the introduction of rGO on the crystal structure and electrochemical performance were discussed. The incorporation of both La and rGO was found to enhance the active surface area and improve conductivity, resulting in the enhanced electrocatalytic performance of rGO/La/NiWO4/GCE, including a wide linear range (0.01-500 μM), a low detection limit (0.0058 μM) and high sensitivity (1.778 μA μM-1 cm-2). The fabricated sensor was further used for DPA detection in fresh apple extract to evaluate its practicality and demonstrated excellent recoveries ranging from 99.52 to 104.70%.

A label-free electrochemical sensor constructed with layer-by-layer assembly of GCE-AuNPs-Q[7]·HAuCl4 for detection of diphenylamine

Metal-organic frameworks (MOFs) including cucurbit[7]uril block (Q[7]·HAuCl₄) were employed to develop a diphenylamine (DPA) sensor in electrochemical method, the presence of HAuCl₄ improved the conductivity of the macrocyclic compound. To further enhance of the sensitivity, Au nanoparticles were inserted between the surface of glassy carbon electrode and Q[7]·HAuCl₄ MOFs (GCE-AuNPs-Q[7]·HAuCl₄). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) were applied for evaluation on the electrochemical behavior. For the electrochemical inertness of DPA, a label-free electrochemical sensor in 5 mM K₃[Fe(CN)₆] solution was achieved, to produce a limit of detection as low as 4.6 µM in a linear range of 5-1000 µM with good reproducibility, high stability and acceptable anti-interference ability. Application of the proposed electrode for the quantitative determination of DPA in tap water and apple juice confirms its real value.

Tailored construction of one-dimensional TiO2/Au nanofibers: Validation of an analytical assay for detection of diphenylamine in food samples

We report a one-dimensional titanium dioxide encapsulated with gold heterojunction nanofibers (TiO₂/Au NFs) as robust electrocatalysts for electrochemical detection of diphenylamine (DPA). A TiO₂/Au NFs were successfully synthesized by a coaxial electrospinning method. The formation of TiO₂/Au NFs was confirmed by various analytical and spectroscopic approaches. The fabricated TiO₂/Au NFs modified screen-printed carbon electrodes (SPCE) exhibit a well-enhanced detection activity towards DPA sensing as compared to other electrodes. Under the experimental conditions, the proposed electrode leading to the sensing range from 0.05 to 60 µM with a detection limit of 0.009 µM was obtained for the DPA detection. Moreover, the TiO₂/Au NFs/SPCE showed good selectivity towards the electrochemical oxidation of DPA. Interestingly, the TiO₂/Au NFs modified electrode was then applied to detect the effect of DPA on spiked content in the food samples.

Surfactant-Assisted Synthesis of Praseodymium Orthovanadate Nanofiber-Supported NiFe-Layered Double Hydroxide Bifunctional Catalyst: The Electrochemical Detection and Degradation of Diphenylamine

Physiological storage disorders are caused by ineffective post-harvest handling of horticultural crops, particularly fruits. To address these post-harvest concerns, diphenylamine (DPAH^•+) is widely used as a preservative to prevent fruit degradation and surface scald during storage around the world. Humans are negatively affected by the use of high concentrations of DPAH^•+ because of the various health complications related to its exposure. As a result, accurate detection and quantification of DPAH^•+ residues in treated fruits are critical. Rare earth metal orthovanadates, which have excellent physical and chemical properties, are potential materials for electrochemical sensors in this area. Herein, we present a simple and direct ultrasonication technique for the surfactant-assisted synthesis of praseodymium orthovanadate (PrVO₄ or PrV) loaded on nickel iron layered double hydroxide (NiFe-LDH) synthesized with deep eutectic solvent assistance, as well as its application as an effective catalyst in the detection and degradation of DPAH^•+ in fruits and water samples. The current work presents supreme electrochemical features of a PrV@NiFe-LDH-modified screen-printed carbon electrode (SPCE) where cetyltrimethylammonium bromide (CTAB) surfactant-driven fabrication of PrV directs the formation of highly qualified engineered structures and the deep eutectic solvent based green synthesis of NiFe-LDH creates hierarchical lamellar structures following the principles of green chemistry. PrV and NiFe-LDH combine to produce a synergistic effect that improves the number of active sites, charge transfer kinetics, and electronic conductivity. Differential pulse voltammetry analysis of PrV@NiFe-LDH/SPCE reveals a dynamic working range (0.005-226.26 μM), increased sensitivity (133.13 μA μM^-1 cm^-2), enhanced photocatalytic activity, and low detection limit (0.001 μM), which are considered significant when compared with the former reported electrodes in the literature for the determination of DPAḢ⁺ for its real-time applications.

Electrocatalytic detection of noxious antioxidant diphenylamine in fruit samples with support of Cu@nanoporous carbon modified sensor

Herein, the facile synthesis of copper(II) and benzene-1,3,5-tricarboxylate (Cu-BTC) and copper nanoporous carbon (Cu@NPC) for the electrochemical detection of diphenylamine (DPA) was systematically investigated. The Cu-BTC and Cu@NPC materials structural, morphological, and thermal stability were evaluated and confirmed using FE-SEM, HR-TEM, XRD, FT-IR, and TGA. The electrocatalytic behavior of sensor materials was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It is presumed that the structural stability and synergic effect exhibited in Cu@NPC are favorable for enhanced sensitivity and selectivity towards the detection of DPA. The Cu@NPC exhibited a wide linear range (0.09-396.82 μM) and the lowest limit of detection (5 nM). Furthermore, the real sample analysis of the sensor for the detection of DPA in apples and pears confirms its potential capability in practical application.

Development of Two-Dimensional Nanomaterials Based Electrochemical Biosensors on Enhancing the Analysis of Food Toxicants

In recent times, food safety has become a topic of debate as the foodborne diseases triggered by chemical and biological contaminants affect human health and the food industry's profits. Though conventional analytical instrumentation-based food sensors are available, the consumers did not appreciate them because of the drawbacks of complexity, greater number of analysis steps, expensive enzymes, and lack of portability. Hence, designing easy-to-use tests for the rapid analysis of food contaminants has become essential in the food industry. Under this context, electrochemical biosensors have received attention among researchers as they bear the advantages of operational simplicity, portability, stability, easy miniaturization, and low cost. Two-dimensional (2D) nanomaterials have a larger surface area to volume compared to other dimensional nanomaterials. Hence, researchers nowadays are inclined to develop 2D nanomaterials-based electrochemical biosensors to significantly improve the sensor's sensitivity, selectivity, and reproducibility while measuring the food toxicants. In the present review, we compile the contribution of 2D nanomaterials in electrochemical biosensors to test the food toxicants and discuss the future directions in the field. Further, we describe the types of food toxicity, methodologies quantifying food analytes, how the electrochemical food sensor works, and the general biomedical properties of 2D nanomaterials.

Hydrophobic deep eutectic solvent-based ultrasonic-assisted liquid-liquid micro-extraction combined with HPLC-FLD for diphenylamine determination in fruit

In this paper, novel high extraction efficiency hydrophobic eutectic solvents (DESs), n-octanoic acid as a hydrogen bond donor (HBD) and menthol as a hydrogen bond acceptor (HBA), were selected from five hydrophobic DESs to extract trace diphenylamine (DPA) in fruits apple, pear and orange under ultrasonic-assisted liquid-liquid micro-extraction (UA-LLME) technology before high-performance liquid chromatography (HPLC) analysis. Working parameters such as the DESs type, molar ratio, extractant volume, and ultrasonic time of the LLME hydrophobic DESs technology were optimised. Average recoveries between 96% and 108% were obtained on actual samples. This method gave lower detection limit (LOD) than other existing methods due to combining the high-efficiency extraction of hydrophobic DES and high sensitivity of fluorescence detector. This method was sensitive and eco-friendly, and can be used for the determination of trace components in fruits.

Simple sonochemical synthesis of lanthanum tungstate (La2(WO4)3) nanoparticles as an enhanced electrocatalyst for the selective electrochemical determination of anti-scald-inhibitor diphenylamine

In this work, lanthanum tungstate (La₂(WO₄)₃) nanoparticles (NPs) were synthesized by facile sonochemical method (elmasonic P, under-sonication 37/100 kHz, ~60 W energy) and utilized as an electrode material for the selective and sensitive electrochemical determination of anti-scald inhibitor diphenylamine (DPA). The synthesized La₂(WO₄)₃ NPs were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDAX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The results revealed that the sonochemically synthesized La₂(WO₄)₃ nanoparticles were with high crystallinity and uniformly distributed nanoparticles like structure. The as-prepared lanthanum tungstate NPs exhibited an excellent electrocatalytic behavior for DPA determination with the lowest detection limit of 0.0024 µM, wide linear range response of 0.01-58.06 µM and a remarkable sensitivity of 1.021 µA µM^-1 cm^-2. Furthermore, La₂(WO₄)₃ NPs showed a good recovery to DPA in apple juice sample. Besides, the electrochemical mechanism of the DPA oxidation reaction was provided in detail.

Electrochemical detection of toxic anti-scald agent diphenylamine using oxidized carbon nanofiber encapsulated titanium carbide electrocatalyst

Two dimensional (2D) titanium carbide (Ti-C) is an analogues of graphene have tremendous attention in recent years due to their high electrical conductivity and catalytic activity. Herein, we have synthesized Ti-C micro particles based on the template-assisted method and subsequently integrated with oxidized carbon nanofiber (f-CNF) through ultrasonication technique. The prepared Ti-C/f-CNF composite was subjected to various structural and morphological characterization techniques including the X-ray diffraction (XRD), scanning electron microscope (SEM), Energy Dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The all followed studies confirmed the formation and crystalline nature of prepared Ti-C/f-CNF nanocomposite. Further, the proposed Ti-C/f-CNF composite modified electrode was successfully applied as an electrocatalyst for the electrochemical detection of diphenylamine (DPA) in food. DPA is known as an anti-scald agent used to post harvest treatment of fruits. However, the higher concentration of DPA causes some hazardous side effects to human. Thus, the detection of DPA is an important concern in healthcare research. Eventually, the proposed Ti-C/f-CNF/SPCE exhibited ultra-low detection limit of (0.003 μM) with a linear range of 0.04-56.82 μM towards the detection of DPA. Moreover, the practicability of the proposed sensor was tested by real sample analysis by using fresh apple extract. Remarkably, the proposed sensor showed an excellent recovery range from 106.8% to 108% for the detection of DPA in spiked apple extract. Finally, we concluded that the integration of f-CNF with Ti-C is significantly enhanced both electrical conductivity and electrocatalytic activity for sensor application.

Estimating Diphenylamine in Gunshot Residues from a New Tool for Identifying both Inorganic and Organic Residues in the Same Sample

A method involving the collection and determination of organic and inorganic gunshot residues on hands using on-line in-tube solid-phase microextraction (IT-SPME) coupled to miniaturized capillary liquid chromatography with diode array detection (CapLC-DAD) and scanning electron microscopy coupled to energy dispersion X-ray (SEM-EDX), respectively, for quantifying both residues was developed. The best extraction efficiency for diphenylamine (DPA) as the main target among organic residues was achieved by using a dry cotton swab followed by vortex-assisted extraction with water, which permits preservation of inorganic residues. Factors such as the nature and length of the IT-SPME extractive phase and volume of the sample processed were investigated and optimized to achieve high sensitivity: 90 cm of TRB-35 (35% diphenyl, 65% polydimethylsiloxane) capillary column and 1.8 mL of the processed sample were selected for the IT-SPME. Satisfactory limit of detection of the method for analysis of DPA deposited on shooters’ hands (0.3 ng) and precision (intra-day relative standard deviation, 9%) were obtained. The utility of the described approach was tested by analyzing several samples of shooters’ hands. Diphenylamine was found in 81% of the samples analyzed. Inorganic gunshot residues analyzed by SEM-EDX were also studied in cotton swab and lift tape kit samplers. Optical microscopy was used to see the inorganic gunshot residues in the cotton swab samplers. The lift tape kits provided lesser sensitivity for DPA than dry cotton swabs—around fourteen times. The possibility of environmental and occupational sources could be eliminated when DPA was found together with inorganic residues. Then, the presence of inorganic and organic residues in a given sample could be used as evidence in judicial proceedings in the forensic field.

Electrochemical sensing of free radical antioxidant diphenylamine cations (DPAH˙+) with carbon interlaced nanoflake-assembled MgxNi9−xS8 microspheres

The detection and control of free radical antioxidant diphenylamine cations (DPAH˙⁺), a typical organic industrial waste water byproduct, is important for environmental safety and protection.

Ultrasound-assisted synthesis of two-dimensional layered ytterbium substituted molybdenum diselenide nanosheets with excellent electrocatalytic activity for the electrochemical detection of diphenylamine anti-scald agent in fruit extract

Metal chalcogenides with large active sites have been received great attention as an excellent catalyst due to their hierarchical structural properties. Here, we have demonstrated the synthesis of ytterbium-doped molybdenum selenide (YbMoSe₂) in the form of two-dimensional nanosheets by using a simple ultrasonic method. The formation of the crystal phase of prepared YbMoSe₂ nanosheets was studied by using the selective characterization techniques. The reported HRTEM confirmed that the introduction of heterogeneous spin of Yb with MoSe₂ creates the lattice distortion. Thus, the active sites can be increased by creating the lattice distortion on the basal plane of the metal chalcogenides nanosheets. The band gap study was carried out by using UV-visible spectrometer and demonstrated the decreasing band gap of MoSe₂ from 1.30 eV to 1.15 eV due to the Yb substitution/doping. The increasing active sites with decreasing band gap facilitate an excellent electronic conductivity and electrochemical activity. Furthermore, the electrocatalytic activity of YbMoSe₂ modified glassy carbon electrode (YbMoSe₂/GCE) toward the sensing of diphenylamine (DPA) anti-scald agent. As expected, YbMoSe₂/GCE showed a high level of electrochemical activity with a low limit of detection (0.004 µM) and excellent sensitivity (11.4 µA µM^-1 cm^-2) towards the detection of DPA. In addition, the superior selectivity, stability, and reproducibility of YbMoSe₂/GCE also were recorded. The beneficial electrochemical activity of YbMoSe₂/GCE offered the more advantages to detection of DPA in the food sample also.

Novel molecularly imprinted polymer based on β-cyclodextrin@graphene oxide: Synthesis and application for selective diphenylamine determination

A sensitive and selective molecularly imprinted polymer (MIP) for the determination of diphenylamine (DPA) was developed based on host-guest interactions of a cyclodextrin-based polymer which possesses an inherent affinity for the target. The proposed GO@MIP has been prepared using the graphene oxide (GO) sheets as surface of polymerization, DPA as target molecule, β-cyclodextrin (β-CD) and acrylamide (AM) as functional monomers, azobisisobutyronitrile (AIBN) as initiator and N, N methylene bisacrylamide (MBAm) as crosslinker which denoted as GO@MIP nanocomposite. The MIP sites were formed by the inclusion complex through interaction of DPA and β-CD, followed by extraction of target. The resulting GO@MIP nanocomposite possess a fast adsorption kinetics, highly improved imprinting effect, high adsorption capacity, and it can be applied to fast extraction of DPA. The resultant GO@MIP nanocomposite was characterized using the Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) analysis. On the other hand, the non-imprinted polymer (GO@NIP nanocomposite) has been synthesized and was used in the adsorption experiments. The MIP exhibited good affinity with a maximum adsorption capacity of 95.98mgg^-1 and excellent selectivity toward DPA than other structural analogues such as 2-amino benzophenone and dithizone.

Ionic liquid coated magnetic core/shell Fe3O4@SiO2 nanoparticles for the separation/analysis of linuron in food samples

Three hydrophobic ionic liquids (ILs) including 1-butyl-3-methylimidazole hexafluorophosphate ([BMIM]PF6), 1-hexyl-3-methyl-imidazole hexafluorophosphate ([HMIM]PF6), and 1-octyl-3-methylimidazole hexafluoro-phosphate ([OMIM]PF6) coated Fe3O4@SiO2 nanoparticles with core-shell structure to prepare magnetic solid phase extraction agent (Fe3O4@SiO2@ILs) and establish a new method of magnetic solid phase extraction (MSPE) coupled with UV spectrometry for separation/analysis of linuron. The results showed that linuron was adsorbed rapidly by Fe3O4@SiO2@[OMIM]PF6 and eluanted by ethanol. Under the optimal conditions, preconcentration factor of the proposed method was 10-fold. The linear range, detection limit, correlation coefficient (R) and relative standard deviation (RSD) were found to be 0.04-20.00 μg mL(-1), 5.0 ng mL(-1), 0.9993 and 2.8% (n=3, c=4.00 μg mL(-1)), respectively. The Fe3O4@SiO2 nanoparticles could be used repeatedly for 10 times. This proposed method has been successfully applied to the determination of linuron in food samples.