Simple and sensitive determination of trace nitrite in water by zero-crossing first-derivative synchronous fluorescence spectrometry using 6-amino-1,3- naphthalenedisulfonic acid as a new fluorescent probe

A violet light-emitting diode-based gas-phase molecular absorption device for measurement of nitrate and nitrite in environmental water

A simple and sensitive device for the detection of nitrite and nitrate in environmental waters was developed based on visible light gas-phase molecular absorption spectrometry. By integrating a detection cell (DC), semiconductor refrigeration temperature-controlling system (SRTCY), and nitrite reactor into a sequential injection analysis system, trace levels of nitrite and nitrate in complex matrices were successfully measured. A low energy-consuming light-emitting diode (violet, 400-405 nm) was coupled with a visible light-to-voltage converter (TSL257) to measure the gas-phase molecular absorption. To reduce the interference of water vapor, an SRTCY was used to condense the water vapor on-line before the gas-phase analyte entered the DC. The DC was radiatively heated by the SRTCY to avoid water vapor condensation in the light path. As a result, the obtained baseline noise reduced 3.75 times than that of without SRTCY. Under the optimized conditions, the device achieved limits of detection (3σ/k) of 0.055 and 0.36 mmol/L (0.77 and 5.04 mg N/L) for nitrite and nitrate, respectively, and the linear calibration ranges were 0.1-15 mmol/L (R2 = 0.9946) and 1-10 mmol/L (R2 = 0.9995), respectively. Precisions of 5.2 % and 9.0 % were achieved for ten successive determinations of 0.3 mmol/L nitrite and 1.0 mmol/L nitrate, and the analytical times for nitrite and nitrate determination were 5 and 13 min, respectively. This method was validated against standard methods and recovery tests, and it was applied to the measurement of nitrite and nitrate in environmental waters. Moreover, a device was designed to enable the field measurement of nitrite and nitrate in complex matrices.

Utilization of a micellar matrix for simultaneous spectrofluorimetric estimation of alfuzosin hydrochloride and vardenafil hydrochloride

A sensitive and direct spectrofluorimetric method was developed for simultaneous quantitation of two co-administered drugs, namely, alfuzosin hydrochloride (AFH) and vardenafil hydrochloride (VRH). Both drugs exhibited native fluorescence properties that could be exploited to assay them in biological fluids with high sensitivity. Spectrofluorimetric analysis of AFH and VRH is based on excitation of both drugs at 265 nm where emission spectra were recorded separately for AFH and VRH at 380 and 485 nm, respectively. Micellar trends in analytical chemistry were adopted to minimize both environmental and occupational hazards, using distilled water and sodium dodecyl sulphate (serves as a micellar medium that enhanced the sensitivity of AFH and VRH) for analysis of both drugs in their raw materials, tablets, and human biological fluids (plasma and urine). Linearity ranges were 1.0-16.0 and 10.0-700.0 ng mL^-1 for AFH and VRH, respectively. The proposed method was successfully assessed for analysis of AFH and VRH in spiked human plasma and urine samples over the following concentrations: 1.0-12.0 ng mL^-1 and 4.0-400.0 ng mL^-1 for both drugs, simultaneously with mean recoveries of 101.08 % and 102.06 % in plasma and 96.75 % and 92.8 % in urine. Statistical analysis of the practical results has proved quite good agreement and revealed there were no significant differences in the accuracy and precision with those obtained by the comparison methods. The proposed method was applied successfully to Prostetrol® and Powerecta® commercial tablets without interference with tablet additives.

A novel near-infrared fluorescent sensor for zero background nitrite detection via the "covalent-assembly" principle

Different chemical states of nitrogen are present in many freshwater and marine ecosystems, and nitrite ions are one of the most toxic water-soluble nitrogen species. Developing an effective and convenient sensing method to constantly detect the concentration of nitrite has become a wide concern. Here, a novel near-infrared fluorescent probe (AAC) was designed and synthesized via the "covalent assembly" principle, showing excellent selectivity and high sensitivity for nitrite. A new nitrite-quantitative method was established with the help of AAC, and the detection limit of nitrite using the new method was as low as 6.7 nM. AAC was successfully applied for the quantitative detection of nitrite in real-world environmental and food samples (including river water and Chinese sauerkraut), and the detection results were essentially identical to the results obtained from the traditional Griess assay. Moreover, AAC was successfully applied for tracking nitrite in Escherichia coli by fluorescence imaging. Since nitrite can have devastating effects, the method established with AAC allowed us to "see" effectively about the water quality, food quality, etc.

Redox-derivatization reaction-based rapid and sensitive determination of nitrite using resonance Rayleigh scattering method

It remains a problem for direct detection of small inorganic nitrite ions using resonance Rayleigh scattering (RRS) method based on the direct dye-binding reaction. In the present study, a redox-derivatization reaction taking only 5 min was introduced prior to nitrite detection. In the redox-derivatization reaction, nitrite ions were reduced by excess iodine ions to generate triiodide ions (I₃^-), which were further derivatized with a cationic dye (basic violet 1, BV1) to form the ion associates of I₃^--BV1. Therefore, the RRS signal was significantly enhanced, resulting from the increase of particle size and resonance-enhanced scattering effect. The analytical procedure was performed by just mixing nitrite, oxidant, acid, and dye all-in-one, avoiding the tediousness of a multi-step process or the preparation of nanoparticles. The whole detection process including the redox-derivatization reaction was less than 6 min. The reaction conditions such as concentration of hydrochloric acid, potassium iodide, and BV1, reaction time, and temperature were investigated. Under optimum conditions, the concentration of nitrite was linear with an RRS signal of I₃^--BV1 ion associates at 320 nm in the range of 0.015-1.2 mg/L. The limit of detection (LOD) was calculated to be 3.0 μg/L. The RRS method was applied to the determination of nitrite in real samples such as pork sausage, milk powder, and water with recovery of 95.2-112%. With advantages of rapidness, high sensitivity, and high selectivity, the method indicates potential applicability for detection of nitrite in complex samples. The method also provides an instructive protocol for detection of analytes that generate no/weak RRS enhancement after the direct dye-binding reaction. Graphical abstract.

A colorimetric fluorescent probe for rapid and specific detection of nitrite

The method of fluorescent probes has been an important technique for detection of nitrite (NO₂ ^- ). As an important inorganic salt, excessive nitrite would threaten humans and the environment. In this paper, a colorimetric fluorescent probe P-N (1,2-diaminoanthraquinone) with rapid response and high selectivity, which could detect NO₂ ^- by visual colour changes and fluorescence spectroscopy is presented. The probe P-N solution (pH 1) changed from pink to colourless with the addition of NO₂ ^- and fluorescence intensity at 639 nm clearly decreased. Good linear exists between fluorescence intensities and NO₂ ^- concentrations for the range 0-16 μM, and the detection limit was 54 nM (based on a 3σ/slope). Moreover, probe P-N could also detect NO₂ ^- in real water samples, and results were all satisfactory. Probe P-N shows great practical application value for detecting NO₂ ^- in the environment.

Sensitive and selective colorimetric nitrite ion assay using silver nanoparticles easily synthesized and stabilized by AHNDMS and functionalized with PABA

Nitrite ions (NO₂ ^-), as one of the important inorganic anions, exhibit considerable effects towards the environment and human health. Moreover, over intake of this anion may cause dangerous diseases. Herein, we successfully fabricated silver nanoparticles (AgNPs) using 4-amino-5-hydroxynaphthalene-2, 7-disulphonic acid monosodium salt (AHNDMS) and functionalized them with p-aminobenzoic acid (PABA), and used the functionalised AgNPs as a sensitive and selective colorimetric sensor for nitrite ions. The structure of the as-prepared pure AgNPs was experimentally characterized by different characterizations methods, namely, UV-vis, FT-IR, CV, DPVs, SEM, TEM, and XRD. Additionally, the nitrite ion sensitively and selectively changes the brownish yellow color of the dispersed AgNPs to pinkish red, indicating aggregation of AgNPs, with a detection limit of 0.016 ppm (0.348 μM) and 0.0069 ppm (0.149 μM) by the naked-eye and by UV-vis spectroscopy, respectively. The color change suggested that the aggregation of AgNPs was induced by nitrite-selective diazo-coupling. UV-vis spectra show the disappearance of the absorbance at 474 nm and appearance of a new peak at 532 nm, presumably due to the conversion of AgNPs to silver ions. Moreover, the studies of interference in the proposed sensor confirm its selectivity in the presence of anions as well as cations. Furthermore, linearity was observed between the absorption and the concentration of nitrite ions. More importantly, the proposed sensor was practicably applied for the determination of nitrite in different water samples, such as distilled water, river water, and tap water.

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.

Ultrasensitive and bifunctional ZnO nanoplates for an oxidative electrochemical and chemical sensor of NO2: implications towards environmental monitoring of the nitrite reaction

Herein, we focused on the one pot synthesis of ZnO nanoplates (NP edge thickness of ∼100 nm) using a chemical emulsion approach for chemical (direct) and electrochemical (indirect) determination of NO₂.