| || || Water -- Analysis|
| || || Catalytic kinetic method for the determination of nitrite and its application in water and vegetables|
Author: Halafihi, Tuikolongahau.
Institution: University of the South Pacific.
Subject: Nitrites -- Analysis, Water -- Analysis, Catalysis -- Fiji, Food -- Analysis
Call No.: Pac TX 572 .N5 H35 2008
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: Nitrite is an active form of nitrogen cycle, resulting from incomplete oxidation of ammonia or from reduction of nitrates. Nitrite is also a versatile chemical agent, which has numerous applications ranging from dye manufacture, fertilizers in agriculture and as corrosion inhibitors to food preservation. Under ordinary conditions nitrite levels in water are low. However, the increasing use of nitrate/nitrite as a preservative in the food industry and as corrosion inhibitor in industrial process, water results in increased levels due to uncontrolled wastewater release by the industries. The environmental impacts caused by the build-up of high nitrite concentrations are significant concerns. Fresh vegetables are the major vehicles for the entry of nitrate (nitrite) into the human system. Nitrate upon reduction to nitrite can cause methaemoglobinaemia or act as precursor in the endogenous formation of carcinogenic nitrosamines. The high content of nitrite in vegetables, other food products and waters is thus a serious threat to human health. Therefore, nitrite determination is important for environment and for public health. Because of these properties the development of analytical methods for very low concentration of nitrite are of interest for application to environmental and vegetables samples. The present study was conducted to establish a catalytic kinetic method (CKM) to investigate the nitrite contents of few commonly consumed fresh and frozen leafy (Chinese cabbage, English cabbage, spinach, lettuce); root (carrot, potato, radish and sweet potato) and fruit (tomato, bean, cucumber, cauliflower and pumpkin) vegetables from Suva municipal market in Fiji. A catalytic kinetic procedure for nitrite determination based on its catalytic effect on the oxidation of brilliant cresyl blue (BCB) by bromate ion in acidic media is standardised and proposed. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of BCB at its .max 595nm. The calibration graph is linear from 1 90 ng mL-1 of nitrite. The detection limit is 0.1 ng mL-1 of nitrite. Nitrite in the range of 1-80 ng mL-1 has been determined successfully where recoveries were 96 - 103.7% with the relative standard deviation 0.03-0.8%. The effect of many foreign ions upon determination of 70 ng mL-1 on nitrite has been studied and shown that most common cations and anions do not interfere in the determination except Fe2+, which was masked by the addition of EDTA. Three extraction techniques (extraction by blending, extraction by heating and alkaline extraction) have been assessed for nitrite extraction from the selected vegetables. The proposed procedure has been successfully applied for the determination of nitrite in wastewater, river water, seawater and vegetable samples with satisfactory results. The typical feature of this procedure is that nitrite determination can be carried at normal temperature of 25oC with analysis time of four minutes.