Determination of nitrite in food samples by anodic voltammetry using a modified electrode

Fabrication of Cu@Ag core-shell/nafion/polyalizarin: Applications to simultaneous electrocatalytic oxidation and reduction of nitrite in water samples

In this study, a Cu@Ag core-shell was synthesized using a co-precipitation method. To create a new electrochemical sensor, a Cu@Ag core-shell with conductive polymers such as polyalizarin yellow R (PA) and Nafion (Nf) was immobilized on the surface of a glassy carbon electrode (Cu@Ag-Nf/PA/GCE). X-ray diffraction analysis (XRD), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FTIR) techniques were employed to characterize the Cu@Ag-Nf/PA/GCE. This modified electrode was used to measure nitrite ions in the water samples. Electrochemical analysis of nitrite was conducted using differential pulse voltammetry (DPV) and cyclic voltammetry (CV) methods. For the first time, the results indicated that the Cu@Ag-Nf/PA nanocomposite demonstrated excellent performance in simultaneously electrocatalyzing oxidation at two specific potentials (0.17V and 0.98V denoted as OX1 and OX2 peaks) and one reduction potential (-0.42 V as a Red peak) for nitrite ions. This research showed various advantages, including applications in linear ranges, sensitivities, and detection limits in three potential areas (OX1, OX2, and Red) by elucidating the mechanism of action of the new electrode for detecting nitrite ions in water samples.

A novel premixing strategy for highly sensitive detection of nitrite on paper-based analytical devices

BACKGROUND

Nitrite has been involved in many food processing techniques and its excessive consumption is closely related to the development of different diseases. Therefore, highly sensitive detection of nitrite is significant to ensure food safety.

RESULT

This study presents a simple and novel strategy for the highly sensitive detection of nitrite in food using paper-based analytical devices (PADs). In this proposed strategy, the nitrite present in the sample undergoes efficient diazotization when initially mixed with sulfanilamide solution before reacting with N-(1-naphthyl) ethylenediamine dihydrochloride (NED) coated on the detection region of the PAD, leading to the maximum production of colored azo compounds. Specifically, within the concentration range of 0.1-20 mg/L, the LOD and LOQ for the nitrite assay using the premixing strategy are determined as 0.053 mg/L and 0.18 mg/L, respectively which significantly surpass the corresponding values of 0.18 mg/L (LOD) and 0.61 mg/L (LOQ) achieved with the regular Griess reagent analysis.

SIGNIFICANCE

The study highlights the critical importance of the premixing strategy in nitrite detection. Under optimized conditions, the strategy demonstrates an excellent limit of detection (LOD) and limit of quantification (LOQ) for nitrite detection in eight different meat samples. In addition to its high precision, the strategy is applicable in the field of nitrite analysis. This strategy could facilitate rapid and cost-effective nitrite analysis in real food samples, ensuring food safety and quality analysis.

CuONPs/MWCNTs/carbon paste modified electrode for determination of tramadol: theoretical and experimental investigation

A practical technique was applied to fabricate CuO nanostructures for use as the electrocatalyst. The green synthesis of cupric oxide nanoparticles (CuO NPs) via co-precipitation is described in this paper using an aqueous extract of Origanum majorana as both reductant and stabilizer, accompanied by characterization via XRD, SEM, and FTIR. The XRD pattern revealed no impurities, whereas SEM revealed low agglomerated spherical particles. CuO nanoparticles and multi wall carbon nanotubes (MWCNTs) have been used to create a modified carbon paste electrode. Voltammetric methods were used to analyze Tramadol using CuONPs/MWCNT as a working electrode. The produced nanocomposite showed high selectivity for Tramadol analysis with peak potentials of ~ 230 mV and ~ 700 mV and Excellent linear calibration curves for Tramadol ranging from 0.08 to 500.0 µM with a correlation coefficient of 0.9997 and detection limits of 0.025. Also, the CuO NPs/MWCNT/CPE sensor shows an an appreciable sensitivity of 0.0773 μA/μM to tramadol. For the first time the B3LYP/LanL2DZ, quantum method was used to compute DFT to determine nanocomposites' connected energy and bandgap energy. Eventually, CuO NPs/CNT was shown to be effective in detecting Tramadol in actual samples, with a recovery rate ranging from 96 to 104.3%.

Ion-selective electrodes based on laser-induced graphene as an alternative method for nitrite monitoring

Nitrite is an important food additive for cured meats; however, high nitrite levels pose adverse health effects to humans. Hence, monitoring nitrite concentration is critical to comply with limits imposed by regulatory agencies. Laser-induced graphene (LIG) has proven to be a scalable manufacturing alternative to produce high-performance electrochemical transducers for sensors. Herein, we expand upon initial LIG studies by fabricating hydrophilic and hydrophobic LIG that are subsequently converted into ion-selective sensors to monitor nitrite in food samples with comparable performance to the standard photometric method (Griess method). The hydrophobic LIG resulted in an ion-selective electrode with improved potential stability due partly to a decrease in the water layer between the electrode and the nitrite poly(vinyl) chloride-based ion-selective membrane. These resultant nitrite ion-selective sensors displayed Nernstian response behavior with a sensitivity of 59.5 mV dec-1, a detection limit of 0.3 ± 0.1 mg L-1 (mean ± standard deviation), and a broad linear sensing range from 10-5 to 10-1 M, which was significantly larger than currently published nitrite methods. Nitrite levels were determined directly in food extract samples of sausage, ham, and bacon for 5 min. These sensor metrics are significant as regulatory agencies limit nitrite levels up to 200 mg L-1 in finished products to reduce the potential formation of nitrosamine (carcinogenic compound). These results demonstrate the versatility of LIG as a platform for ion-selective-LIG sensors and simple, efficient, and scalable electrochemical sensing in general while demonstrating a promising alternative to monitor nitrite levels in food products ensuring regulatory compliance.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

Nitrate, nitrite and nitrosamines in the global food supply

Inorganic nitrate provided by either nitrate salts or food supplements may improve cardiometabolic health. However, current methods to assess dietary nitrate, nitrite and nitrosamine consumption are inadequate. The purpose of this study was to develop a reference database to estimate the levels of nitrate, nitrite and nitrosamines in the global food supply. A systematic literature search was undertaken; of the 5,747 articles screened, 448 met the inclusion criteria. The final database included data for 1,980 food and beverages from 65 different countries. There were 5,105 unique records for nitrate, 2,707 for nitrite, and 954 for nitrosamine. For ease of use, data were sorted into 12 categories; regarding nitrate and nitrite concentrations in food and beverages, 'vegetables and herbs' were most reported in the literature (n = 3,268 and n = 1,200, respectively). For nitrosamines, 'protein foods of animal origin' were most reported (n = 398 records). This database will allow researchers and practitioners to confidently estimate dietary intake of nitrate, nitrite and nitrosamines. When paired with health data, our database can be used to investigate associations between nitrate intake and health outcomes, and/or exercise performance and could support the development of key dietary nitrate intake guidelines.

Electrochemical Sensor Based on Iron(II) Phthalocyanine and Gold Nanoparticles for Nitrite Detection in Meat Products

Nitrites are widely used in the food industry, particularly for the preservation of meat products. Controlling the nitrate content in food is an important task to ensure people's health is not at risk; therefore, the search for, and research of, new materials that will modify the electrodes in the electrochemical sensors that detect and control the nitrate content in food products is an urgent task. In this paper, we describe the electrochemical behavior of a glass carbon electrode (GCE), modified with a Fe(II) tetra-tert-butyl phthalocyanine film (FePc(tBu)₄/GCE), and decorated with gold nanoparticles (Au/FePc(tBu)₄/GCE); this electrode was deposited using gas-phase methods. The composition and morphology of such electrodes were examined using spectroscopy and electron microscopy methods, whereas the main electrochemical characteristics were determined using cyclic voltammetry (CV) and amperometry (CA) methods in the linear ranges of CV 0.25-2.5 mM, CA 2-120 μM in 0.1 M phosphate buffer (pH = 6.8). The results showed that the modification of bare GCEs, with a Au/FePc(tBu)₄ heterostructure, provided a high surface-to-volume ratio, thus ensuring its high sensitivity to nitrite ions of 0.46 μAμM^-1. The sensor based on the Au/FePc(tBu)₄/GCE has a low limit of nitrite detection at 0.35 μM, good repeatability, and stability. The interference study showed that the proposed Au/FePc(tBu)₄/GCE exhibited a selective response in the presence of interfering anions, and the analytical capability of the sensor was demonstrated by determining nitrite ions in real samples of meat products.

Improved spectrophotometric method for nitrite determination in processed foods and dietary exposure assessment for Korean children and adolescents

A spectrophotometric method based on diazo-coupling reaction for nitrite analysis was established and validated, including inter-laboratory validation, linearity, accuracy, precision, the limit of detection (LOD) and limit of quantification (LOQ). The time-saving and high-recovery method was established by examining the filtration step, colorimetric process and concentration range of the calibration curve. This method showed good linearity (r² > 0.999) in the range of 0.025-1.0 μg/mL. The three-level recoveries were between 86.7% and 108.6%, with the coefficient of variation (CV) below 5.8%. Mean nitrite concentration ranges in processed foods were ND-33.47 mg/kg. The mean nitrite intake was 0.8% of the Acceptable Daily Intake (ADI, 0.07 mg/kg bw/day) for all children and adolescents and 2.8% for the consumer group. The major contributors for all subjects and consumers were ham, sausage and bacon. These results indicated that the improved method was suitable for analyzing nitrite in processed foods and the nitrite exposure levels were safe.

Surface Engineering of Carbon Fiber Paper toward Exceptionally High-Performance and Stable Electrochemical Nitrite Sensing

In this work, we introduce our recent finding that the carbon fiber paper (CFP) treated by simple air annealing (OCFP) could be used for exceptionally high-performance electrochemical nitrite sensing. The air-annealing process endows the pristine CFP with higher defective edge/plane sites, more oxygen-containing functional groups, higher roughness, and improved wettability. The electrochemical studies show that the OCFP exhibits excellent sensing performance for nitrite, with an ultralow determination limit of 0.1 μM and a detection limit of 0.07 μM, an ultrawide linear determination range of 0.1-3838.5 μM, a fast current response of 1 s, and a high sensitivity of 930.4 μA mM^-1 cm^-2. These performance values are comparable or even superior to those for most reported noble- or transition-metal-based advanced nitrite sensors. Besides, this electrode also presents satisfactory stability, reproducibility, and feasibility of nitrite sensing in food samples. As an ideal monolithic and metal-free catalyst with ultrahigh and stable detection performance, the OCFP has a high potential to be integrated into next-generation electrochemical sensing devices.

Can the mechanical activation (polishing) of screen-printed electrodes enhance their electroanalytical response?

The mechanical activation (polishing) of screen-printed electrodes (SPEs) is explored and shown to exhibit an improved voltammetric response (in specific cases) when polished with either commonly available alumina slurry or diamond spray. Proof-of-concept is demonstrated for the electrochemical sensing of nitrite where an increase in the voltammetric current is found using both polishing protocols, exhibiting an improved limit of detection (3σ) and a two-fold increase in the electroanalytical sensitivity compared to the respective un-polished counterpart. It is found that mechanical activation/polishing increases the C/O ratio which significantly affects inner-sphere electrochemical probes only (whereas outer-sphere systems remain unaffected). Mechanical activation/polishing has the potential to be a simple pre-treatment technique that can be extended and routinely applied towards other analytes for an observable improvement in the electroanalytical response.

A new electrochemical sensor for highly sensitive and selective detection of nitrite in food samples based on sonochemical synthesized Calcium Ferrite (CaFe2O4) clusters modified screen printed carbon electrode

Herein, we report a novel, disposable electrochemical sensor for the detection of nitrite ions in food samples based on the sonochemical synthesized orthorhombic CaFe₂O₄ (CFO) clusters modified screen printed electrode. As synthesized CFO clusters were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformer infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and amperometry (i-t). Under optimal condition, the CFO modified electrode displayed a rapid current response to nitrite, a linear response range from 0.016 to 1921 µM associated with a low detection limit 6.6 nM. The suggested sensor also showed the excellent sensitivity of 3.712 μA μM^-1 cm^-2. Furthermore, a good reproducibility, long-term stability and excellent selectivity were also attained on the proposed sensor. In addition, the practical applicability of the sensor was investigated via meat samples, tap water and drinking water, and showed desirable recovery rate, representing its possibilities for practical application.

Polypyrrole with a functionalized multi-walled carbon nanotube hybrid nanocomposite: a new and efficient nitrite sensor

This study mainly focuses on the electrochemical-assisted synthesis of conducting polymers such as polypyrrole (PPy) with sodium dodecyl sulfate (SDS) as a surfactant and supported with functionalized multi-walled carbon nanotubes (f-MWCNTs).

Methods for the detection and determination of nitrite and nitrate: A review

Various techniques for the determination of nitrite and/or nitrate developed during the past 15 years were reviewed in this article. 169 references were covered. The detection principles and analytical parameters such as matrix, detection limits and detection range of each method were tabulated. The advantages and disadvantages of various methods were evaluated. In comparison to other methods, spectrofluorimetric methods have become more attractive due to its facility availability, high sensitivity and selectivity, low limits of detection and low-cost.

Determination of hypochlorite by quenching the fluorescence of 1-pyrenylboronic acid in tap water

In neutral conditions, a new probe based on the oxidative conversion of 1-pyrenylboronic acid to 1-hydroxypyrene was established for the fluorescence signaling of practical hypochlorite.

Hydrophobicity effects in iron polypyridyl complex electrocatalysis within Nafion thin-film electrodes

Four polypyridyl redox catalysts Fe(bp)₃²⁺, Fe(ph)₃²⁺, Fe(dm)₃²⁺, and Fe(tm)₃²⁺ (with bp, ph, dm, and tm representing 2,2′-bipyridine, 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine, and 3,4,7,8-tetramethyl-1,10-phenanthroline, respectively) are investigated for the electrocatalytic oxidation of three analytes (nitrite, arsenite, and isoniazid).

Polymer/carbon nanotubes coated graphite surfaces for highly sensitive nitrite detection

This study describes the preparation of poly(vinylferrocenium)/multi-walled carbon nanotubes (PVF(+)/MWCNTs) coated electrode and its use for sensitive electrochemical nitrite detection. PVF(+)/MWCNTs composite coated disposable pencil graphite electrode (PVF(+)/MWCNTs/PGE) was prepared by electropolymerization of poly(vinylferrocene) (PVF) in the presence of MWCNTs with one-step electropolymerization. Characterization of PVF(+)/MWCNTs/PGE was carried out with scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Then electrochemical detection of nitrite was performed using differential pulse voltammetry (DPV). Nanocomposite coated electrode showed high sensitivity to nitrite with a detection limit of 0.1 μM. The electrode platform was successfully applied to a commercial mineral water sample.

Electrochemical response of nitrite and nitric oxide on graphene oxide nanoparticles doped with Prussian blue (PB) and Fe2O3 nanoparticles

Electrocatalytic behaviour of graphene oxide (GO), iron(iii) oxide (Fe₂O₃) and Prussian blue (PB) nanoparticles towards nitrite (NO₂⁻) and nitric oxide (NO) oxidation was investigated on a platinum modified electrode.

Determination of nitrite in real food and water samples by a novel terbium-macrocycle complex

A novel terbium-macrocycle complex (Tb-Ac) was designed and synthesized for selective and sensitive sensing towards NO₂⁻ in real food and water samples, as well as living cells, in terms of reliable accuracy and practicability.

Polymeric optical sensors for selective and sensitive nitrite detection using cobalt(III) corrole and rhodium(III) porphyrin as ionophores

Cobalt(III) 5,10,15-tris(4-tert-butylphenyl) corrole with a triphenylphosphine axial ligand and rhodium(III) 5,10,15,20-tetra(p-tert-butylphenyl) porphyrin are incorporated into plasticized poly(vinyl chloride) films to fabricate nitrite-selective bulk optodes via absorbance measurements. The resulting films yield sensitive, fast and fully reversible response toward nitrite with significantly enhanced nitrite selectivity over other anions including lipophilic anions such as thiocyanate and perchlorate. The selectivity patterns differ greatly from the Hofmeister series based on anion lipophilicity and are consistent with selectivity obtained with potentiometric sensors based on the same ionophores. The optical nitrite sensors are shown to be useful for detecting rates of emission of nitric oxide (NO) from NO releasing polymers containing S-nitroso-N-acetyl-DL-penicillamine.