Determination Of Nitrite In Saliva Research Articles

Colorimetric determination of nitrite in clinical, food and environmental samples using microfluidic devices stamped in paper platforms

Paper microfluidic devices were explored to perform the colorimetric determination of nitrite in saliva, sausage, ham, preservative water and river water samples with no statistical difference from a reference method.

Determination of nitrite in saliva using microfluidic paper-based analytical devices

Point-of-care platforms can provide fast responses, decrease the overall cost of the treatment, allow for in-home determinations with or without a trained specialist, and improve the success of the treatment. This is especially true for microfluidic paper-based analytical devices (μPAD), which can enable the development of highly efficient and versatile analytical tools with applications in a variety of biomedical fields. The objective of this work was the development of μPADs to identify and quantify levels of nitrite in saliva, which has been proposed as a potential marker of periodontitis. The devices were fabricated by wax printing and allowed the detection of nitrite by a colorimetric reaction based on a modified version of the Griess reaction. The presented modifications, along with the implementation of a paper-based platform, address many of the common drawbacks (color development, stability, etc.) associated with the Griess reaction and are supported by results related to the design, characterization, and application of the proposed devices. Under the optimized conditions, the proposed devices enable the determination of nitrite in the 10–1000μmolL−1 range with a limit of detection of 10μmolL−1 and a sensitivity of 47.5AU [log (μmolL−1)]−1. In order to demonstrate the potential impact of this technology in the healthcare industry, the devices were applied to the analysis of a series of real samples, covering the relevant clinical range.

Amperometric detection with microelectrodes in flow injection analysis: theoretical aspects and application in the determination of nitrite in saliva

The construction of a wall-jet cell with amperometric detection using a set of disc electrodes whose radii ranged from 5 to 750 μm has been proposed. The influence of some experimental parameters like flow rate and electrode radius on hydrodynamic voltammograms recorded for a 0.5 mmol dm −3 potassium ferrocyanide solution also containing 0.1 mol dm −3 KCl has been discussed. Some considerations regarding the current signals obtained from flow injection experiments using both a 5- and a 750-μm radius platinum electrode were carried out in order to achieve the lowest limit of detection, a value of 0.03 μmol dm −3 ferrocyanide being calculated by using the 5-μm radius microelectrode as amperometric detector. The wall-jet cell has been used in the determination of nitrite in saliva by quantifying the triiodide formed in the reaction of the analyte with excess iodide in acidic medium. A 12.5-μm platinum disc microelectrode maintained at +0.2 V vs. Ag/AgCl was used as amperometric detector. Peaks obtained in fiagrams after injection of diluted saliva to the carrier stream containing 0.1 mol dm −3 sulphuric acid and 20 mmol dm −3 potassium iodide were compared to an analytical curve obtained in the same conditions ( r 2=0.997) for a nitrite concentration in the range 1–10 μmol dm −3. The concentration of nitrite in the saliva sample after the appropriate correction for dilution was found to be 2.3 ppm (0.05 mmol dm −3), in a good agreement with results obtained by using a standard spectrophotometric procedure (2.5 ppm). The limit of detection of the method was calculated as 0.2 μmol dm −3, and the reproducibility was checked by measuring the peak current for 19 injections of 10 μM nitrite, the standard deviation being 3.7%.

Electrochemical sensor of nitrite based on an inorganic film modified glassy carbon electrode

The electrocatalysis of nitrite in solutions at an inorganic film modified glassy carbon electrode was studied. The modifier was an electrodeposited thin inorganic film of the copper-heptacyanonitrosylferrate (CuHNF). Cyclic voltammetry of the modified electrode in a nitrite solution revealed that both oxidation and reduction of nitrite were catalyzed and the electrocatalytic currents were controlled by the diffusion of nitrite. Voltammetric and amperometric responses were investigated. When applied as an amperometric sensor in a flow injection system, the modified electrode permitted detection at — 0.55 V, over 500 mV lower than at the naked electrode surface. A linear response range extending from 1 × 10−6 to 1 × 10−3M nitrite was obtained, with a detection limit of 3 × 10−7M. The relative standard deviation for 50 repetitive injections with a 5 × 10−5M nitrite solution was less than 4%. The procedure was applied to the determination of nitrite in saliva and nitrate.

Development of a sensor for the detection of nitrite using a glassy carbon electrode modified with the electrocatalyst [Os(bipy) 2(PVP) 10Cl]Cl

The electrocatalytic polymer [Os(bipy) 2(PVP) 10Cl]Cl, where bipy = 2,2′-bipyridyl and PVP = poly(4-vinylpyridine), was used to modify glassy carbon for use in planar flow cells and conventional electrochemical cells for the reductive electrochemical detection of nitrite. The electrocatalyst accelerates a slow electrochemical reduction of nitrite via a two-step reduction process resulting in a 70-fold increase in response compared with the unmodified electrode. The detector response was evaluated with regard to flow-rate, applied potential, electrolyte pH and surface coverage of the polymer film. A mechanism for the two-step reduction process is proposed. The detector response appears to be limited by the rate constant of the mediated electrochemical reaction. A linear response range extending from 5 × 10 −6 to 1 × 10 −2 M nitrite was obtained, with a detection limit of 0.23 ng ml −1 for the planar flow cell and 0.23 ng ml −1 for a conventional electrochemical cell. The performance of the sensor was assessed with respect to stability, selectivity and interference. The sensor was applied to the determination of nitrite in saliva.

Fluorometric determination of nitrite with 4-hydroxycoumarin.

A simple, sensitive, and reproducible fluorometric method for determination of nitrite has been developed. This method is based on the nitrosation of 4-hydroxycoumarin in acidic medium and subsequent reduction to 3-amino-4-hydroxy-coumarin, which is fluorescent in alkaline medium. The fluorescence intensity is proportional to the nitrite concentration in the range of 3 ng/mL to 1 ..mu..g/mL in the sample solution, with a relative standard deviation of 0.5% (50 ng/mL). The method has been applied to the determination of nitrite in saliva.