Determination of nitrates, nitrites and oxalates in food products by capillary electrophoresis with pH-dependent electroosmotic flow reversal

Underutilized green leafy vegetables: frontier in fortified food development and nutrition

From the ancient period, Green leafy vegetables (GLV) are part of the daily diet and were believed to have several health beneficial properties. Later it has been proved that GLV has outstanding nutritional value and can be used for medicinal benefits. GLV is particularly rich in minerals like iron, calcium, and zinc. These are also rich in vitamins like beta carotene, vitamin E, K, B and vitamin C. In addition, some anti-nutritional elements in GLV can be reduced if it is grown properly and processed properly before consumption. Tropical countries have a wide variety of these green plants such as Red Spinach, Amaranth, Malabar Spinach, Taro Leaf, Fenugreek leaf, Bengal Gram Leaves, Radish Leaves, Mustard Leaves, and many more. This review focuses on listing this wide range of GLVs (in total 54 underutilized GLVs) and their compositions in a comparative manner. GLV also possesses medicinal activities due to its rich bioactive and nutritional potential. Different processing techniques may alter the nutritional and bioactive potential of the GLVs significantly. The GLVs have been considered a food fortification agent, though not explored widely. All of these findings suggest that increasing GLV consumption could provide nutritional requirements necessary for proper growth as well as adequate protection against diseases caused by malnutrition.

Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications

Oxalate is an antinutrient present in a wide range of foods, with plant products, especially green leafy vegetables, being the main sources of dietary oxalates. This compound has been largely associated with hyperoxaluria, kidney stone formation, and, in more severe cases, systematic oxalosis. Due to its impact on human health, it is extremely important to control the amount of oxalate present in foods, particularly for patients with kidney stone issues. In this review, a summary and discussion of the current knowledge on oxalate analysis, its extraction conditions, specific features of analytical methods, reported occurrence in foods, and its health implications are presented. In addition, a brief conclusion and further perspectives on whether high-oxalate foods are truly problematic and can be seen as health threats are shown.

Cobalt-Nitrogen Co-Doped Carbon as Highly Efficient Oxidase Mimics for Colorimetric Assay of Nitrite

Transition metal-N-doped carbon has been demonstrated to mimic natural enzyme activity; in this study, cobalt-nitrogen co-doped carbon (Co-N-C) nanomaterial was developed, and it could be an oxidase mimic. Firstly, Co-N-C with oxidase-like activity boosts the chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) to produce the oxidized TMB (oxTMB). And the aromatic primary amino group of oxTMB reacts with nitrite (NO₂^-) to form diazo groups. Based on this background, we developed a cascade system of a Co-N-C-catalyzed oxidation reaction and a diazotization reaction for nitrite determination. The low detection limit (0.039 μM) indicates that Co-N-C is superior compared with the vast majority of previously reported nitrite assays. This study not only provides a novel nanozyme with sufficiently dispersed active sites, but it also further applies it to the determination of nitrite, which is expected to expand the application of nanozymes in colorimetric analysis.

Determination of nitrate and nitrite levels in enteral nutrition formula marketed in Turkey: A risk assessment study

In this study, the nitrite and nitrate levels of 37 enteral nutrition formulas of three different international brands marketed in Turkey were evaluated using high-performance liquid chromatography with diode-array detection (HPLC-DAD). Also, risk assessment of non-carcinogenic was calculated by models including hazard quotient (HQ) and hazard index (HI) in the deterministic model. Enteral nutrition formula consumption amounts obtained from individuals between the ages of 6-36 volunteers voluntarily participated in the study, and health risk assessments were calculated. The range of concentration of nitrate levels in enteral formulas of brands (B1, B2, and B3) was determined as 11.08 ± 2.88 (2.90-15.79), 11.64 ± 3.39 (2.92-22.93), and 10.66 ± 3.46 (4.92-15.37) mg/kg, respectively. The range of concentration of nitrite levels in enteral formulas of brands (B1, B2, and B3) was determined as 4.18 ± 1.10 (1.86-5.82), 3.70 ± 1.25 (1.29-5.26), and 3.38 ± 1.67 (2.00-5.29) mg/kg, respectively. The mean nitrate and nitrite levels of exposure from consumption of enteral nutrition formulas were determined as 0.14 and 0.11, 0.06 and 0.07 mg/kg bw/day for females and males, respectively. Nitrate and nitrite exposure levels calculated in the study did not exceed the ADI threshold values given by JECFA. The average HQ value calculated for the exposure of nitrate to male and female individuals was less than 1. Still, the P95 values calculated for nitrate were greater than 1.00 except for female and male individuals (24-36 ages). The HI value was found to be greater than 1.00 in all age groups of both genders. The presence of nitrites and nitrates in enteral nutrition formulas may lead to health problems in sensitive groups.

A turn-on fluorescent nano-probe base on methanobactin-AuNPs for simple and efficient detection of nitrite

Nitrite ions are important markers threatening humans and environmental security. A highly selective method for rapid detection of nitrite needs to be developed. Herein, a novel and rapid fluorescence method for nitrite determination is established on the basis of diazotization-coupling reaction of methanobactin (Mb) extracted by Methylosinus trichosporium OB3b with nitrite on the fluorescence. In the presence of gold nanoparticles (AuNPs), the fluorescence of AuNPs was strongly quenched by the Mb because the sulfhydryl or amino structures on the surface of Mb could be bound to the surface of AuNPs by forming Au-S or Au-N bonds. Upon addition of nitrite, the Mb easily reacts with nitrite to form azo products in the acidic medium. Then, with the increase of nitrite concentration, the Mb-AuNPs fluorescence was gradually recovered, realizing the turn-on fluorescence sensing of nitrite. Under optimal conditions, the proposed method has a good linear relationship with nitrite concentration in the range of 0-8.0 μM and 8.0-50.0 μM, and the detection limit is 16.21 nM. In addition, satisfactory results were obtained for nitrite analysis using milk, ham sausage and leaf mustard as real samples, which demonstrated that the method as-developed would have great practical application prospects.

The first harmonised total diet study in Portugal: Nitrate occurrence and exposure assessment

A harmonised TDS methodology was used to assess the Portuguese population's nitrate baseline dietary exposure and the risk of exceeding the Acceptable Daily Intake (ADI). Nitrate occurrence in 164 TDS samples pooled based on 20 FoodEx2 groups, representative of 18 to 75 years old population diet, was determined using UV-HPLC. The 'vegetables' group had the highest mean nitrate concentration (353 mg/kg), followed by 'starchy roots' (62 mg/kg), 'composite dishes' (53 mg/kg) and 'fruits' (46 mg/kg). Lettuce contained the most nitrates (1729 mg/kg). The estimated mean nitrate exposure of 1.17 mg/kg bw/day, with 3.18% of individuals exceeding the ADI, was assessed on a semi-probabilistic approach using the MCRA software. Lettuce (28%) contributed most to nitrate exposure followed by vegetable soup (13%). Processed meat contribution to exposure was 0.86% and 2.44% (overall population and consumers only). At population level the nitrate estimated exposure (mean and 95th percentile) revealed no reason for concern.

Bifunctional Mn-Doped N-Rich Carbon Dots with Tunable Photoluminescence and Oxidase-Mimetic Activity Enabling Bimodal Ratiometric Colorimetric/Fluorometric Detection of Nitrite

Multimodal detection is a promising paradigm because of its advantages of expanding usage scenarios and improving reliability. However, it is very challenging to design reasonable strategies to achieve the multimodal sensing of targets. Herein, we developed an unprecedented bimodal ratiometric colorimetric/fluorometric method by exploring a novel bifunctional artificial oxidase mimic, Mn-doped N-rich carbon dots (Mn-CDs), to achieve the high-performance determination of nitrite in complicated matrices. The Mn-CDs exhibited both tunable photoluminescence and high oxidase-like activity, effectively catalyzing the colorless 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to generate blue TMB⁺. When nitrite was introduced, the TMB⁺ species generated would specifically react with nitrite to produce diazotized TMB⁺, resulting in a color change from blue to green and finally to yellow. Simultaneously, the fluorescence of Mn-CDs was quenched by the diazotized TMB⁺ product via the inner filter effect. Hence, the existence of nitrite could lead to the simultaneous variations of visual color and photoluminescence, providing the principal basis for the bimodal ratiometric colorimetric/fluorometric quantification of the target. With the method, excellent sensitivity, selectivity, reliability, and practicability for nitrite detection were verified. Our work proposes a new bimodal strategy for nitrite measurement using bifunctional CDs-based enzyme mimics, which will inspire future effort on the exploration of promising multifunctional nanozymes and their advanced applications in biochemical sensing.

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.

Dual determination of nitrite and iron by a single greener sequential injection spectrophotometric system employing a simple single aqueous extract from Areca catechu Linn. serving as a natural reagent

Dual determination of nitrite and iron was proposed by using a single greener sequential injection (SI) spectrophotometric system employing a simple single aqueous extract from Areca catechu Linn. The extract served as a natural reagent to replace N-(1-naphthyl)ethylenediamine (NED) of the Griess reagent with nitrite and 1,10-phenanthroline with iron. The color products possessed analytical wavelengths at 430 and 560 nm, respectively. Conditions for the SI procedure were optimized using a univariate experimental design. Calibration ranges were up to 5.0 mg L⁻¹ and 10.0 mg L⁻¹ with limits of detection (LODs) of 0.04 mg L⁻¹ and 0.05 mg L⁻¹ for nitrite and iron(iii), respectively, and relative standard deviations (RSDs) being less than 3%. Recoveries of spiked standard nitrite and iron(iii) at 0.3 mg L⁻¹ and 0.5 mg L⁻¹ in water samples were 88 to 104% and 84 to 109%, respectively. The developed method successfully achieved dual determination of nitrite and total iron agreeing at a 95% confidence level with the reference methods of the conventional Griess assay and flame atomic absorption spectrometry (FAAS), respectively. The proposed method utilized locally available material from plants and serves the UN-SDGs.

Dual determination of nitrite and iron was proposed by using a single greener sequential injection (SI) spectrophotometric system employing a simple single aqueous extract from Areca catechu Linn.

Transporters and tubule crystals in the insect Malpighian tubule

The insect renal (Malpighian) tubules are functionally homologous to the mammalian kidney. Accumulating evidence indicates that renal tubule crystals form in a manner similar to mammalian kidney stones. In Drosophila melanogaster, crystals can be induced by diet, toxic substances, or genetic mutations that reflect circumstances influencing or eliciting kidney stones in mammals. Incredibly, many mammalian proteins have distinct homologs in Drosophila, and the function of most homologs have been demonstrated to recapitulate their mammalian and human counterparts. Here, we discuss the present literature establishing Drosophila as a nephrolithiasis model. This insect model may be used to investigate and understand the etiology of kidney stone diseases, especially with regard to calcium oxalate, calcium phosphate and xanthine or urate crystallization.

Rapid pyrolysis of Cu2+-polluted eggshell membrane into a functional Cu2+-Cu+/biochar for ultrasensitive electrochemical detection of nitrite in water

Bioremediation is one of efficient methods to solve the issues of water or soil contaminated by metal ions. However, the harvested biowaste is often troublesome to handle owing to the second pollution. Herein, the waste eggshell membrane was used to adsorb Cu²⁺ in wastewater, which was then converted into biochar containing copper ions (Cu²⁺-Cu⁺/Biochar) via a rapid pyrolysis. By integrating the collective advantages of eggshell membrane and Cu²⁺-Cu⁺, such as superior electrical conductivity, enlarged electrochemically active surface area, unique three-dimensional porous network characteristics, and fast charge transport, the Cu²⁺-Cu⁺/Biochar system can be used as a self-supporting sensor for detection of nitrite (NO₂^-). The sensor demonstrated superior electrochemical sensing abilities accompanied by a broad linear range (1-300 μM), ultralow detection limit (0.63 μM), and high sensitivity (30.0 μA·mM^-1·cm^-2). In addition, the fabricated electrochemical sensor has excellent stability, good reproducibility, and strong anti-interference performance. More importantly, the sensor has a high recovery rate when it is used to detect nitrite in tap water, mineral water, and sausage, indicating the feasibility of using this sensor in practical applications. This study provides a green and sustainable approach for simultaneous treatment of biomass waste eggshell membrane, remedy of heavy metals, and electrochemical detection of nitrite.

Fluorescent and colorimetric dual-readout sensor based on Griess assay for nitrite detection

In this work, we presented a sensitive and selective colorimetric and fluorescent dual-readout sensor based on Griess assay for nitrite (NO₂^-) detection under acidic condition. The sensor system was constituted of acid-resistant carbon quantum dots (CQDs) and 3-aminophenol (3-Aph) with acidic condition regulated using HCl. During the sensing procedure, reaction of 3-Aph and NO₂^- under acidic condition can yield a yellow-colored azoic compound (AZO), which gives the colorimetric readout; meanwhile, the fluorescence of CQDs (fluorescence reporter) quenched due to the strong absorption of AZO, leading to fluorescent readout. Wherein, CQDs were synthesized via hydrothermal method through using polyacrylamide as precursor and characterized by AFM, XRD and XPS. Under the optimized condition, the sensor exhibit broad linear relationships towards NO₂^- in the range of 10 to 100 nM and 2.5 to 100 μM, with practical detection limits of 10 nM and 2.5 μM for the fluorescent and colorimetric readout, respectively. And the sensor displayed excellent capability of selectivity according to interferences study. Furthermore, testing of sprouts, bacon and ham sausage real samples demonstrated good recoveries and reproducibility of the sensor system. All these results suggested the presented colorimetric and fluorescent dual-readout sensor can be a promising candidate for the NO₂^- detection in real applications.

The nitrate content of fresh and cooked vegetables and their health-related risks

BACKGROUND

Vegetables are the most important source of nitrates in the human diet. During various processes in the body, nitrates are converted into nitrites, which causes various diseases, such as blue baby syndrome and cancer. This study aimed to determine the concentration of nitrates in several vegetable farms in Sanandaj city and to evaluate their health-related risks.

METHODS

This descriptive cross-sectional study was conducted from October 2017 to July 2018. A total of 90 samples were taken from nine farms. Soil and water sampling was also carried out. All stages of sample preparation and extraction were carried out according to Food Standards 2-16721, and the nitrate measurements were performed using ion chromatography (Compact IC Plus 882 Model, Metrohm, Switzerland). A health risk assessment was performed using the non-carcinogenic risk assessment.

RESULTS

This study's results showed that the nitrate concertation in all vegetables was less than National Iranian Vegetable Nitrate Standard. Nitrate levels in leafy vegetables were higher than in root vegetables, and the root vegetables levels were higher than those in Fruit vegetable. The nitrate level in vegetables in autumn was higher than in spring. The cooking process reduced the raw vegetables' nitrate content from 4.094% to 13.407%, while the frying process increased the vegetables' nitrate content from 12.46% to 29.93%. The highest health risk level in raw, cooked and fried vegetables was parsley, parsley and beet leaves, respectively, and the lowest in all categories was tomatoes. Generally, the highest health risk was related to fried beet leaves, and the lowest was raw tomatoes. In addition, each of the abovementioned relationships between vegetables' nitrate levels and the harvest season, type of processing procedure and type of vegetables was significant (p < 0.05). The irrigation water's nitrate concentration in all fields was between 12.36 and 33.14 mg/l. The soil contained nitrate levels of between 4.35 and 9.7 mg/kg.

CONCLUSION

Based on this study, we can conclude that the amount of nitrates in raw vegetables was lower than the standard limit's level and that this level does not cause health problems for consumers.

Porous ionic liquid polymer: A reusable adsorbent with broad operating pH range for speciation of nitrate and nitrite

Ionic liquids (ILs) are a class of fluids with unique physicochemical properties employing polymeric substances emerging new materials. Solidification of ILs into porous materials generates porous ionic liquid polymers that combine the unique characteristics of ILs with common porous materials and polymers. In this study, it's the first time the porous ionic liquid polymer was chosen as a sorbent for extraction and speciation of nitrite and nitrate. Porous IL was prepared through polymerization of 1-allyl-3-methylimidazolium bromide monomers in the presence of azobisisobutyronitrile (AIBN) and crosslinking of ethylene glycol dimethyl acrylate (EGDMA). Parameters affecting the adsorbent performance were optimized. Under the optimal conditions, correlation coefficient (R²) was 0.9996 and LOD was 0.1 µg L^-1. This method presented the linearity in the concentration range between 0.1-100 µg L^-1 and the relative standard deviation was 3.2%. Finally, the adsorption behavior of the obtained sorbent for nitrate and nitrite determination in various real samples was evaluated. The result indicates that the porous ionic liquid polymer showed high adsorption capacity (233 mg g^-1). The convenient preparation of the porous ionic liquid material, as well as high adsorption capacity for anionic pollutants predicted its broad application potential in anion removal materials.

Certification of nitrate in spinach powder reference material SPIN-1 by high-precision isotope dilution GC-MS

A high-precision exact-matching quadruple isotope dilution method (ID⁴MS) was employed for the quantitation of nitrate in an air-dried spinach powder Certified Reference Material (CRM). The analyte was extracted in hot water following addition of ¹⁵NO[Formula: see text] internal standard. The blend was then treated with sulfamic acid to remove nitrite and with triethyloxonium tetrafluoroborate to promote aqueous conversion of nitrate into volatile EtONO₂. The derivative was analyzed by headspace GC-MS with 3-min elution time. The method performance was validated with a series of tests which demonstrated adequate selectivity and ruggedness. This method supported the development of novel SPIN-1 CRM giving a modest contribution to its uncertainty (u_char = 0.85%). With respect to previous attempts, the SPIN-1 was proven stable, homogeneous (u_hom = 0.44%), and suitable for spinach monitoring under EU regulations. On dried basis, the nitrate content of SPIN-1 was found to be 22.53 ± 0.43 mg/g (U_c = 1.9%, k = 2). The material was also used in an inter-laboratory study where four laboratories employed a total of ten measurement methods. Graphical Abstract SPIN-1 Certified Reference Material for nitrate in spinach powder.

Analysis of Leafy Vegetable Nitrate Using a Modified Spectrometric Method

A quick and cost-effective method to analyze leafy vegetable nitrate on spectrometry was developed and compared with a standard method using high performance liquid chromatography (HPLC). This method was designed to use ion-exchange solid phase extraction (SPE) cartridges in reducing interference from organic matrices to meet the criterion of an existing method for analyzing nitrate in wastewater. Nine vegetables (bok coy, cabbage, celery, Chinese cabbage, Chinese kale, lettuce, mustard green, pak choi, and water spinach) were selected for the method testing with three replicates being conducted for each vegetable. The nitrate contents ranged from 800 to 4,300 μg/g, with bok coy, celery, and pak choi being the highest. Data derived from spectrometry and HPLC were close to each other with most relative errors being within ±10% and were highly correlated with an R square value of 0.969. Stability testing and spike analysis resulted in a mean coefficient of variation lower than 6% and a mean recovery rate of 83.7%, suggesting reliability of the method. In addition, both the cost and time consumption for using this method were lower than the standard method using HPLC or ion chromatography, making this spectrometric method a good alternative for analysis of leafy vegetable nitrate.

Polyethylenimine-Capped CdS Quantum Dots for Sensitive and Selective Detection of Nitrite in Vegetables and Water

In the present work, polyethylenimine-capped CdS quantum dots (PEI-CdS QDs) with bright green fluorescence were synthesized and applied for sensitively and selectively detecting the nitrite in vegetable and water samples. Highly fluorescent and environment-friendly PEI-CdS QDs (quantum yield about 8%) with diameters of ca. 5 nm were easily synthesized by using hyperbranched PEI as functional polymer. Formation of the PEI-CdS QDs was verified by transmission electron microscopy and UV-vis spectroscopy. The fluorescence intensity of the as-synthesized PEI-CdS QDs was enhanced pronouncedly by the increasing amount of PEI and was stable when the pH ranged from 5.0 to 9.0. Our results demonstrated that the fluorescence of the PEI-CdS QDs was effectively quenched by the nitrite in a rather wide linear range of 1.0 × 10^-7-1.0 × 10^-4 M while efficiently avoiding the interferences from nitrate ions and other commonly coexisting anions of nitrite in the vegetable samples. The detection limit of the present method was lower than the maximum limit of nitrite in drinking water (6.5 × 10^-5 M) ruled by the World Health Organization, which is significant to the application of the method.

Determination of Food Oxalates Using Silica-Titania Xerogel Modified with Eriochrome Cyanine R

The interaction of silica–titania xerogel with triphenylmethane dyes (pyrocatechol violet, chrome azurol S, eriochrome cyanine R) has been investigated to create a new sensor material for solid phase spectrophotometric determination of food oxalates. The complex forming reaction between xerogel incorporated titanium(IV) and triphenylmethane dyes has been studied; half-reaction periods, complex composition, equilibrium constants, and xerogel sorption capacity have been calculated for each dye. Eriochrome cyanine R (ECR) is characterized by the shortest half-reaction period, the smallest equilibrium constant, and the greatest capacity; it has been chosen for the sensor material construction because titanium(IV)-ECR complex is formed faster and can be destroyed easier than other studied complexes. The interaction of this sensor material with oxalates has been described: the presence of oxalates causes sensor material discoloration and the absorbance is used as analytical signal. The analytical range is 35–900 mg/L (LOD 10.5 mg/L, n = 7). High concentrations of interfering inorganic anions, organic acids, and sucrose did not affect oxalate determination. Proposed solid phase spectrophotometric procedure has been successfully applied for the determination of oxalates in food samples (sorrel, spinach, parsley, ginger, and black pepper) and the results are in good agreement with HPLC oxalate determination.

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.

A total analytical system featuring a novel solid-liquid extraction chamber for solid sample flow analysis

In this work, a total flow analysis system based on a novel solid-liquid extraction chamber is presented. This strategy enables all the main experimental procedures for the analysis of a solid sample to be performed automatically: enrichment of the liquid extract, sample treatment, filtration of the liquid extract from the solid sample, directing the extract towards detection, and finally cleansing of the chamber for the following solid sample to be analyzed. The chamber designed to be incorporated in the flow manifold presents two main features: it accommodates stirring bars for enhancing the extraction process, and it presents replaceable solid sample containers (a spare part of the solid-liquid extraction chamber) to easily replace the solid sample and therefore enhance sample analysis throughput. The chamber performance was assessed using two different solid samples, an ion exchanger resin and vegetable samples, focussing on proton and nitrate ion extraction, respectively. The main figures of merit achieved were relative standard deviation (RSD) and relative error values below 7 % for all determinations. The determination rate for vegetable samples was ca. 12 samples h-1. The proposed strategy may be exploited to perform automatically the analysis of solid samples as it embodies a simple automatic strategy of a very important but time-consuming and laborious analytical operation. Graphical abstract TAS for solid liquid extraction and nitrate potentiometric determination of vegetable samples.

Au-Pt bimetallic nanoparticles supported on functionalized nitrogen-doped graphene for sensitive detection of nitrite

In this work, we report a novel Au-Pt bimetallic nanoparticles (Au-PtNPs) decorated on the surface of nitrogen-doped graphene (NG) functionalized with 1, 3, 6, 8-pyrene tetra sulfonic acid sodium salt (PyTS) by direct electrodeposition method. The results of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and electrochemical impendence spectrum (EIS) reveal that the Au-PtNPs were successfully anchored on the surface of NG sheets with a diameter of 20-40nm. Further, the prepared Au-PtNPs/PyTS-NG nanocomposite exhibits superior catalytic activity for the oxidation of nitrite. Under optimal experimental conditions, an amperometric sensor with a linear range of 0.5-1621μM and a detection limit of 0.19μM (S/N=3) for the detection of nitrite was set up and applied to real samples.

Rapid and sensitive method for analysis of nitrate in meat samples using ultra performance liquid chromatography-mass spectrometry

A sensitive and selective ultra performance liquid chromatography-mass spectrometric method has been developed for the quantitative analysis of nitrate in meat samples. Selected ion reaction (SIR) mode was adopted to identify and quantify the nitrate. Chromatographic analyses were performed on a BEH C-18 column with a mobile phase consisting of a surfactant (Cetylpyridinium chloride) and acetonitrile in equal ratio (50/50, v/v) at a flow rate of 0.4 mL min(-1). The limit of detection and limit of quantitation of the developed method was found to be 0.0599 and 0.1817 mg kg(-1), respectively. The linearity of the proposed method was checked in the concentration range of 0.5-10 mg kg(-1) with an excellent correlation coefficient (r) of 0.997. The recovery of the nitrate in the meat samples were in the range of 98.02-98.99%.

Spectrophotometric determination of nitrite in soil and water using cefixime and central composite design

The present paper seeks to develop a simple method for the spectrophotometric determination of nitrite in soil and water samples and also measure optimum reaction conditions along with other analytical parameters. The method is based on the diazotization-coupling reaction of nitrite with cefixime and 1-naphthylamine in an acidic solution (Griess reaction). The final product that is an azo dye has an orange color with maximum absorption at 360 nm which Beer's Law is obeyed over the concentration range 0.02-15.00 mg L(-1) of nitrite. Optimal conditions of the variables affecting the reaction were obtained by central composite design (CCD). A detection limit of 4.3×10(-3) mg L(-1) was obtained for determination of nitrite by the proposed method. The proposed method was successfully applied to determine nitrite in soil and water samples. The molar absorptivity of the product of the reaction and RSD in determination of nitrite in real samples are 4.1×10(3) (L mol(-1) cm(-1)) and lower than 10%, respectively.

Adding Molecules to Food, Pros and Cons: A Review on Synthetic and Natural Food Additives

The pressing issue to feed the increasing world population has created a demand to enhance food production, which has to be cheaper, but at the same time must meet high quality standards. Taste, appearance, texture, and microbiological safety are required to be preserved within a foodstuff for the longest period of time. Although considerable improvements have been achieved in terms of food additives, some are still enveloped in controversy. The lack of uniformity in worldwide laws regarding additives, along with conflicting results of many studies help foster this controversy. In this report, the most important preservatives, nutritional additives, coloring, flavoring, texturizing, and miscellaneous agents are analyzed in terms of safety and toxicity. Natural additives and extracts, which are gaining interest due to changes in consumer habits are also evaluated in terms of their benefits to health and combined effects. Technologies, like edible coatings and films, which have helped overcome some drawbacks of additives, but still pose some disadvantages, are briefly addressed. Future trends like nanoencapsulation and the development of "smart" additives and packages, specific vaccines for intolerance to additives, use of fungi to produce additives, and DNA recombinant technologies are summarized.

Development of a selective and pH-independent method for the analysis of ultra trace amounts of nitrite in environmental water samples after dispersive magnetic solid phase extraction by spectrofluorimetry

This paper describes an innovative and rapidly dispersive magnetic solid phase extraction spectrofluorimetry (DMSPE-FL) method for the analysis of trace amounts of nitrite in some environmental water samples. The method includes derivatization of aqueous nitrite with 2, 3-diaminonaphthalene (DAN), analysis of highly fluorescent 2, 3-naphthotriazole (NAT) derivative using spectrofluorimetry after DSPME. The novelty of our method is based on forming NAT that was independent with the pH-responsive and was adsorbed on MMWCNT by hydrophobic attractions in both acidic and basic media. The extraction efficiency of the sorbent was investigated by extraction of nitrite. The optimum extraction conditions for NO2(-) were obtained as of extraction time, 1.5 min; 10mg sorbent from 160 mL of the sample solution, and elution with 1 mL of acetone/KOH. Under the optimal conditions, the calibration curves were obtained in the range of 0.1-80 µg L(-1) (R(2)=0.999) and LOD (S/N=3) was obtained in 34 ng L(-1). Relative standard deviations (RSD) were 0.6 % (five replicates at 5 μg L(-1)). In addition, the feasibility of the method was demonstrated with extraction and determination of nitrite from some real samples containing tap, mineral, sea, rain, snow and ground waters, with the recovery in standard addition to real matrix of 94-102 % and RSDs of 1.8-10.6%.

Analysis of nitrites and nitrates in hams and sausages by open-tubular capillary electrochromatography with a nanolatex-coated capillary column

In this work, a new open-tubular capillary electrochromatography (OT-CEC) method with the nanolatex-coated column was proposed for the determination of nitrites and nitrates in foodstuffs. The method was simple and repeatable as a result of avoiding the introduction of an electroosmotic flow reverse additive (such as cetyltrimethylammonium chloride) in electrophoretic buffer. The limits of quantitation were 0.89 and 1.05 mg kg⁻¹ for nitrate and nitrite, respectively, whereas the overall recoveries ranged from 94 to 103%. The developed OT-CEC method was successfully applied for 12 samples, and the residue profiles of nitrites and nitrates in hams and sausages were obtained and evaluated.

Upconversion nanoparticles for ratiometric fluorescence detection of nitrite

Individual upconversion nanoparticles with green and red emissions were synthesized and used as ratiometric fluorescence probes for the detection of nitrite by selectively turning on the green fluorescence.