Nitrite determination, electrochemical method

Measuring nitrite in food and environmental samples is an important issue as this compound is a human health hazard and may even cause gastric cancer. The determination of nitrite using electrochemical methods offers simple, inexpensive, and faster analysis method compared to some other more expensive and time-consuming techniques such as chromatography or spectrophotometry. Electrochemical determination of nitrite is carried out by either reduction or oxidation methods. However,... 

An indirect electrochemical method developed for nitrite determination may be of general applicability for PAA determination, as shown in equation 13. A nitrite sample is placed into a cell containing a known amount of 3-sulfanilic acid in dilute HC1 at pH 3. After 5 min the diazonium ion formation is complete an excess of catechol (109) is added and the concentration of the remaining 3-sulfanilic acid is determined at +0.12 V with a GCE vs. standard calomel electrode, by measuring the adduct (110) formed between the aromatic amine and the quinone derived from catechol in the diffusion layer of the electrode. The 3-isomer of sulfanilic acid was chosen among the three isomers, aniline and 4-nitroaniline for its highest sensitivity and its lowest LOD, 0.7 pM, with linearity from 20 to 80 pM. A spectrophotometric assay may be carried out for nitrite by measuring at 516 nm the azo dye derived from catechol and the diazonium ion after 3 h ... 

Nitrite and nitrate may also be determined by HPLC using anion-exchange columns with either UV absorption or electrochemical detection. These methods are generally used for environmental samples and urine where fewer interfering compounds exist. The more extensive sample preparation and analysis time have limited its use for biological samples. 

In method (c), the NOC after HPLC separation was photolyzed by a UV lamp (254 10 nm), and the charged nitrite species was determined amperometrically (79). The denitrosation reaction was found to be dependent on the wavelength of the UV light, lamp intensity, exposure time, and pH of the solution. The effluent from the HPLC column was passed through a capillary PTFE tubing coiled around a 40-W mercury lamp. The electrochemical detector used permitted either single- or dual-mode detection corresponding, respectively, to detection limits of 60 pg and 20 pg for NDMA. The method was applied to the determination of NDMA in beer and of... 

This method is free from interferences, which when coupled with the specificity and the high sensitivity of the electrochemical detection mode, renders it suitable for the determination of trace levels of nitrate and nitrite in surface, ground and main water. 

Kim and Kim [6] have described an extremely sensitive determination of nitrite in drinking water (tap water and underground water) and environmental samples (rain, lake water, and soil) by ion exclusion chromatography with electrochemical detection. Potential interferences in the determination of nitrite by the standard spectrophotometric method or by the ion exchange chromatographic method with either conductivity or ultraviolet detection were eliminated. The detection limit was 0.1 pg L 1 without preconcentration. 

Microelectronic technologies have also been used in nitrite biosensors and electrochemical sensors (Suzuki and Taura, 2001 Adhikari and Majumdar, 2004). Ameida et al. (2013) have also developed a method of electrochemical nitrite measurement by means of a gold working electrode covered with 1,2-diaminobenzene (DAB) integrated in a FIA system. This sensor helps improve selectivity, repeatability, stability, and sensitivity. A Nafion/lead-ruthenate pyrochlore electrode chemically modified for determination of NO2 oxidation and NO reduction based on AC-impedance spectroscopy and FIA has also been tested (Zen et al., 2000). Quan and Shin (2010) also tested an electrochemical nitrite biosensor based on co-immobilization of copper-containing nitrite reductase and viologen-modified chitosan (CHIT-V) on a glassy carbon electrode (GCE). 

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