Simultaneous Determination of Nitrate and Nitrite in Fish Products with Improved Sensitivity by Sample Stacking-Capillary Electrophoresis

A Dual-mode Ratiometric Fluorometric and Colorimetric Platform Based on Nitrogen-doped Carbon Dots and o-phenylenediamine for the Detection of Nitrite

In this study, a dual-mode ratiometric fluorometric and colorimetric platform for the determination of nitrite in pickles was proposed by exquisitely employing the fact that non-fluorescent o-Phenylenediamine (OPD) was oxidized by nitrite under acidic conditions to form fluorescent 2,3-diaminophenazine (DAP) (Em = 575), which meanwhile quench the fluorescent nitrogen-doped carbon dots (N-CDs) at 455 nm, the ratio of fluorescence intensity of DAP to N-CDs (F575/F455) changed with the increase of nitrite accompanied by visible color changes. Thus, nitrite can be quantitatively detected within a wide linear range (10-500 µM) with a low detection limit of 0.45 µM due to the high quantum yield of 39.7% of N-CDs. In addition, the colour of the N-CDs/OPD system changed from transparent to yellow when the nitrite was introduced, enabling colorimetric and on-site visual detection. The detection limit of the colorimetric method was 3.03 µM with a linear range of 10-500 µM. The proposed ratiometric fluorometric method has pleasant selectivity and good immunity to interference.

Sample Stacking-Capillary Electrophoretic Analysis of Nitrate and Nitrite in Organic- and Conventional-Originated Baby Food Formulas from Turkey

Commercially available baby food formulas represent a convenient alternative to homemade meals especially in the recent years. The main purpose of this study is the determination of nitrate and nitrite levels by a sample stacking-capillary electrophoresis technique in the baby foods. The baby foods analyzed were organic-originated, vegetable-based, fruit-based, mixed puree, and a vegetable soup. Vegetables and fruits have high nitrate and nitrite concentrations. Nitrate itself is not actually hazardous. However, nitrite has negative health effects. Thus, baby foods have to be strictly controlled due to the potential health risk of nitrite. In this study, the sample stacking method enhanced the sensitivities of both anions. Nitrate contents ranged from 16.1 to 285 mg/kg with a mean concentration of 149 mg/kg for all samples. The lowest nitrate amount belonged to red fruity milky baby food whereas the highest nitrate was found in organic pumpkin, banana, and carrot mixed puree. The nitrite levels in all the samples were below the LOQ value of the analyzed method. As a conclusion, there is no health risk of the analyzed baby foods regarding nitrate and nitrite levels considering the regulations.

Electrochemical Sensing of Nitrite Ions Using Modified Electrode by Poly 1,8-Diaminonaphthalene/Functionalized Multi-Walled Carbon Nanotubes

A novel electrochemical sensor based on conducting polymer and multi-walled carbon nanotubes was reported for the detection of nitrite ions (NO₂⁻). The hybrid material poly 1,8-Diaminonaphthalene (poly 1,8-DAN)/functionalized multi-walled carbon nanotubes (f-MWCNT) was prepared by using a simple electrochemical approach which is based on the deposition of functionalized multi-walled carbon nanotubes (f-MWCNT) on the surface of the electrode followed by the electropolymerization of 1,8-DAN using cyclic voltammetry. The morphology and the electro-catalytic properties of the obtained electrodes were investigated with Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS) showing an improvement of the electronic transfer due to the synergic effect between the proprieties of poly 1,8-DAN and f-MWCNT. Under the optimum experimental conditions, the poly 1,8-DAN/f-MWCNT/CPE exhibited excellent electro-catalytic activity towards nitrite detection. The nitrite anodic peak potential decreased by 210 mV compared to the bare carbon paste electrode. The calibration plot of nitrite detection was linear in the range of concentration from 300 to 6500 nM with a low detection limit of 75 nM.

Sample stacking – Capillary electrophoretic determination of nitrate and nitrite contents as nitric oxide metabolites in honey varieties originated from Anatolia

Nitrate and nitrite ions taken from food are the sources of bioavailable nitric oxide (NO) in the nitrogen cycle. Some beneficial effects of honey on health are attributed to the ability of honey to increase NO production. The variation of nitrate and nitrite levels of honey samples collected from different Anatolia regions were clarified using capillary electrophoresis technique. The sensitivities of both anions were improved with the application of the sample stacking method. Separation buffer consisted of 30 mmol L−1 formic acid and 30 mmol L−1 sodium sulfate at a pH of 4.0. The CE technique revealed that 18 honey samples contained nitrate anion ranged between 2.53 and 31.8 mg kg−1. Nitrite amounts were found in lower amounts in the honey samples as between non-detected and 0.533 mg kg−1. The observed differences in nitrate levels between honey varieties may be a way to determine honey's origin.

Nitrite, biogenic amines and volatile N-nitrosamines in commercial Chinese traditional fermented fish products

To examine the safety of Chinese traditional fermented fish products (CTFPs) available on the Chinese market, nitrite, nitrate, biogenic amines (BAs) and volatile N-nitrosamines (VNAs) content in 33 commercial CTFPs from different provinces was investigated. The mean content of nitrite and nitrate wase 0.63 and 749.5 mg/kg, respectively. Concerning the occurrence of BAs, the accumulation in all CTFPs samples remained at low levels, whereas only in one sample from Guangxi the histamine content exceeded the critical level (50 mg/kg). In addition, six types of VNAs, including N-nitrosodimethylamine (NDMA), N-nitrosoethylmethylamine, N-nitrosopiperidine, N-nitrosopyrrolidine, N-nitrosomorpholine and N-nitrosodiphenylamine, were detected in a high number of samples. The NDMA content in 36.4% of the samples and the total VNAs content in about 63.6% of the samples were unacceptable. Principal component analysis indicated that the accumulation of NDMA and total VNAs was closely related with the content of histamine, tyramine and nitrate.

Development of a Copper-Based Metal Organic Electrode for Nitrite Sensing

BACKGROUND

Nitrite is naturally present in vegetables and added to processed meats to enhance their color and prolong their shelf life. It is of concern because it reacts to form nitrosamines, which have been linked to cancer.

OBJECTIVE

To develop a quick, reliable, and inexpensive method for quantifying nitrite in foods.

METHOD

A copper-based metal organic framework (Cu-MOF)/gold-platinum alloy nanoparticle(Au@Pt)-modified glassy carbon electrode (GCE) was developed via a simple wet chemical synthesis followed by electrochemical deposition of gold-platinum alloy nanoparticles onto the surface of a GCE. Morphological characterization and component analysis of the prepared nanomaterials were carried out by Fourier transform infrared spectroscopy and scanning electron microscopy. Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the electrochemical behavior of the fabricated electrodes.

RESULTS

The quantitative and specific detection of nitrite was obtained by the amperometric i-t method. At a pH of 7, temperature of 25°C, and ionic strength of 0.4 M, the electrode exhibited a linear range of 0.001-12.2 mM nitrite with a low detection limit of 72 nM (S/N = 3).

CONCLUSIONS

The Cu-MOF/Au@Pt/GCE exhibited good repeatability, reproducibility, stability, and selectivity to provide a capable analysis method for food samples.

HIGHLIGHTS

A Cu-MOF with a large surface area and high porosity was developed to provide an electrode with many active sites. The Au@Pt alloy nanoparticle improved the electrocatalytic activity toward nitrite. The synergistic action between the Cu-MOF and Au@Pt alloy nanoparticle enhanced the electrochemical performance of the sensor.

Nitrate and Nitrites in Foods: Worldwide Regional Distribution in View of Their Risks and Benefits

Nitrate and nitrite ions are used as food additives to inhibit the growth of microorganisms in cured and processed meats. Vegetables contain significant quantities of nitrate and nitrite. Actually, the vast majority of consumed nitrate and nitrite comes from natural vegetables and fruits rather than food additives. For years, the cancer risks of these two ions have been discussed, since they potentially convert into the carcinogenic nitrosamines. However, recently, these two ions have been considered essential nutrients which promote nitric oxide production and consequently help cardiovascular health. It seems that the role of these two ions in our diet is important now from a different point of view. In this review, the nitrate and nitrite contents of food products from different countries are displayed globally in order to reinterpret the risks/benefits of our consumption quotations. This review article is based on Science Citation Index (SCI) articles reported between 2008 and 2018.

A simple yet sensitive colorimetric nitrite ions assay based on diazotization with p‑Aminobenzoic and coupling with phloroglucinol in acidic medium

Immoderate intake of nitrite (NO₂^-) is deleterious human health and may result in causing dangerous diseases. In this study, nitrite detection system was successfully fabricated based on a unique diazo-coupling reaction of p‑Aminobenzoic acid (PABA) and phloroglucinol (1, 3, 5‑trihydroxybenzene). Upon the presence of NO₂^- in an acid medium, p‑Aminobenzoic acid could not only form diazonium ion easily but also couple with p‑Aminobenzoic acid, and results forming yellow water-soluble azo dye that shows maximum absorption at 434 nm. Under the further accurate determination condition, such as acid concentration, amount of reagents and time required, the naked-eye detection of NO₂^- showed excellent selectivity in compared with some anions. Especially, diazotization and coupling reaction proposed here is very fast and control of pH and temperature are unnecessary. Moreover, the color is stable for several days and Beer's law is obeyed over a wide range. Reliable detection can be made in the range of 0.05 to 1 p.p.m. of nitrite ion. Detection limit was calculated to be 0.024 p.p.m. (0.52 μ M) by UV-visible spectroscopy and 0.05 p.p.m. (1.09 μ M) by naked-eye. By using an electrochemical method, IR, SEM, and ¹HNMR, the sensing mechanism can be easily verified. More importantly the proposed method was successfully applied for the determination of nitrite in a real water sample.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2016-2018)

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in-line concentration methods in capillaries and microchips, covering the period July 2016-June 2018. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in-line extraction methods that have been used for electrophoresis.

Recent progress of sample stacking in capillary electrophoresis (2016-2018)

Electrophoretic sample stacking comprises a group of capillary electrophoretic techniques where trace analytes from the sample are concentrated into a short zone (stack). This paper is a continuation of our previous reviews on the topic and brings a survey of more than 120 papers published approximately since the second quarter of 2016 till the first quarter of 2018. It is organized according to the particular stacking principles and includes chapters on concentration adjustment (Kohlrausch) stacking, on stacking techniques based on pH changes, on stacking in electrokinetic chromatography and on other stacking techniques. Where available, explicit information is given about the procedure, electrolyte(s) used, detector employed and sensitivity reached. Not reviewed are papers on transient isotachophoresis which are covered by another review in this issue.

Simultaneous determination of parabens and inorganic anions in cosmetics by a two-dimensional ultrahigh-performance liquid chromatography-ion chromatography valve-switching method

Simultaneous determination of parabens and inorganic anions in cosmetics in a single injection was obtained in a two-dimensional UHPLC-IC valve switching system.

Recent progress of sample stacking in capillary electrophoresis (2014-2016)

The term "sample stacking" comprises a relatively broad spectrum of techniques that already form an almost inherent part of the methodology of CZE. Their principles are different but the effect is the same: concentration of a diluted analyte into a narrow zone and considerable increase of the method sensitivity. This review brings a survey of papers on electrophoretic sample stacking published approximately since the second quarter of 2014 till the first quarter of 2016. It is organized according to the principles of the stacking methods and includes chapters aimed at the concentration adjustment principle (Kohlrausch stacking), techniques based on pH changes, micellar methods, and other stacking techniques. Not reviewed are papers on transient ITP that are covered by another review in this issue.

Recyclable Magnetic Mesoporous Nanocomposite with Improved Sensing Performance toward Nitrite

A magnetic nanomaterial for nitrite ion detection was demonstrated in the present study. This nanomaterial was prepared by grafting a rhodamine 6G derivative (denoted as Rh 6G-OH) into the channels of core-shell magnetic mesoporous silica nanospheres. The nanocomposite (denoted as Fe3O4@Rh 6G) showed large surface area and improved fluorescent performance to accumulate and recognize NO2(-), and its superparamagnetic behavior played an important role in reusability. The fluorescent intensity decreased linearly along with the NO2(-) concentration in the range of 1-50 μM, and the detection limit was estimated to be 0.8 μM, which was much lower than the maximum limit of nitrite ion in drinking water (65 μM) recommended by World Health Organization. Importantly, Fe3O4@Rh 6G could be magnetically collected and effectively reutilized after six test cycles.