Kinetic Spectrophotometric Determination of Nitrite Based on Its Catalytic Effect on the Oxidation of Methyl Red by Bromate

Abstract

A precise, sensitive, and accurate catalytic spectrophotometric method for the determination of nitrite in food stuff is presented. In acidic solution, methyl red (MR) is oxidized by bromate to form a colorless compound. The reaction is accelerated by trace amounts of nitrite and can be followed by measuring the absorbance at 520 nm. The absorbance of the reaction mixture decreases with increasing time and reaches to a minimum that is inversely related to the nitrite concentration. The change in absorbance at 25 and 50 sec was calculated as an analytical signal. Under the optimum experimental conditions (0.3 M sulfuric acid, 1.1 × 10⁻⁵ M MR, 2.6 × 10⁻⁴ M bromate, 0.2 M nitrate, and 25°C), nitrite can be determined in the range of 0.05–1.2 µg g⁻¹. The standard deviation is 0.06 for six replications at 0.3 µg g⁻¹.The detection limit as the mean of the blank signals plus three times the blank standard deviation is 0.045 mg kg⁻¹. The method was successfully applied for the determination of nitrite in meat products.

Keywords:

• Kinetic
• Spectrophotometric
• Methyl red
• Nitrite
• Bromate
• Catalytic effect