Flow-Injection Analysis Method for the Determination of Nitrite and Nitrate in Natural Water Samples Using a Chemiluminescence NOx Monitor

Abstract

The determination of nitrite and nitrate in aqueous environmental samples is of considerable interest in research concerning hydrological chemistry, chemical oceanography, and atmospheric chemistry. Nitrate is an essential nutrient which controls the biomass in natural water; the amount also indicates the extent of pollution and eutrophication of the aquatic environment. Nitrite is a nitrogen-cycle intermediate and a useful indicator of the equilibrium state of the oxidative and reductive pathways of the nitrogen cycle. Also, nitric acid and nitrous acid are very important trace constituents of the atmosphere in both the gaseous and particulate phases. Nitric acid is a major NOx sink in photochemical air pollution. Nitrous acid is recognized as a major source of a very reactive hydroxyl radical, which is a key intermediate for all photochemical oxidant formations. These gases and particulates are precursors of acid rain, and are deposited on the ground mainly by wet precipitation, such as rain and snow.Among many analytical methods proposed for the determination of nitrate and nitrite, a widely used method for analyses of natural water samples is based on the reduction of nitrate to nitrite and a subsequent spectrophotometric determination via the Griess reaction, 1-3 which involves the diazotization of sulfanilic acid and successive coupling with 1-naphthylamine. Though numerous modifications have been suggested, primarily based on changing either the reagent being diazotized or coupled, sulfanilamide or sulfanilic acid and N-(1-naphtyl)ethylenediamine are the most popular couples. 4,5 The spectrophotometric method can provide reliable results for natural water samples, but suffers from interferences from suspended and colored substances in the samples. Cox 6 proposed a chemiluminescence analysis technique, which is more highly sensitive and free from these interferences. The technique is based on the chemical reduction of nitrate and nitrite to NO and detection via a chemiluminescence reaction of NO with ozone. Garside 7 first applied this technique to seawater analyses. Braman and Hendrix 8 reported on an application used for environmental water samples. These methods used NaI for reducing nitrite to NO, and iron(II)-molybdate or vanadium(III) for reducing nitrate to NO. The reduction procedures in these methods require highly acidic conditions and/or operation at a relatively high temperature. In the monitoring method of ambient gaseous HNO2, 9 we employed ascorbic acid in a dilute H2SO4 for reducing nitrite to NO. This reagent is easy to handle and the reaction is rapid and quantitative at low nitrite levels. By reducing nitrate to nitrite with an alkaline hydrazine solution, the measurement system was further developed to a gaseous HNO3 monitoring method. 10The coupling of the chemiluminescence detection with a flowinjection technique (FIA) would permit the development of sensitive, precise, rapid, and high throughput methodologies having a wide dynamic range. Aoki and Wakabayashi 11 reported a chemilumine...

A method for nitrite removal in nitrate N and O isotope analyses

“…Reduction of nitrous acid by ascorbate-The pKa 1 of ascorbic acid (AscH 2 ) is 4.2, around which pH the concentration of nitrous acid (HNO 2 ) becomes sufficiently high to engender its spontaneous reduction by ascorbate (AscH -), generating NO (nitric oxide) gas (Kanda and Taira 2003):…”

A chemiluminescence flow injection system for nitrite ion determination

“…Among various methods that have been reported for the determination of nitrite, chemiluminescence-based methods are of great importance for environmental monitoring, water analysis and other applications where the determination of trace amounts of nitrite, or its related compounds, is needed [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Chemiluminescence, as one of the most sensitive detection methods, offers a wide linear range, low detection limit, simple and inexpensive instrumentation and very short analysis time [20].…”

“…However, gas-phase chemiluminescence requires additional devices such as an ozone generator and liquid-gas separator (LGS), and thus more control over the experiment is required. Various methods have been used for the reduction of nitrite and separation of the resulting NO from the liquid-phase [6][7][8][9][10][11][12][13], but the detection of NO in all of these reports has been made with commercial analyzers. It must be noted that mixing of the reactants in the reduction step and separation of NO from the liquid-phase by a fast, efficient and reproducible method is very important, because they strongly affect the sensitivity, precision and detection limit of the measurement.…”

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples*1

“…Several reactions and detection methods have been developed [6][7][8][9][10][11][12]. Some of those are timeconsuming, need heating for acceleration of the detection reaction, sometime solvent extraction is necessary for analyte separation and procedures are rather complicated.…”