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Nitrite ions are one of the harmful compounds for human health. In addition to the available state, nitrite ions are converted from nitrate ions by the microbial reduction in the natural environment. When entering our body, they will react with haemoglobin to form methemoglobin by oxidation of ferrous iron, leading to dangerous methemoglobinemia, also known as blue-baby syndrome. In this study, the determination of nitrite in water and vegetables samples is based on Griess reaction between sulfanilic acid with 1-Naphthylamine. The absorbance was measured at 524 nm after 15-25 minute reaction in acid environment (pH 2.5) at room temperature. There is a good tolerance towards high amount of interfering ions such as nitrate, chloride and ferric ions. The range of linearity was found to be 0.04 ÷ 1.1 mg/L of nitrite. The limit of detection and limit of quantitation were found to be 3.79 x 10-3mg/L and 0.0126 mg/L, respectively. Under these validated conditions, Gries - Ilosvay reagents were successful in quantifying concentrations of nitrite in water and fresh vegetables collected in the South of Vietnam.