The Determination Of Nitrite In Food And Sensitivity Enhancement With Cyclodextrins

It is known that nitrite is wide spread contaminants of food,soil and surface water worldwide.The determination of nitrite and nitrate is of general importance because of their harmful impact on human health.The toxicity of nitrite is primarily due to the fact that it can react with secondary or tertiary amines present in human body to form nitrosamines,and nitrite can react with iron(Ⅲ) of haemoglobin to produce methaemoglobinaemia disease.Thus,the determination of nitrite is of great importance.Cyclodextrin(CD) has influence on optics property of guest-object,such as how to enhance selectivity and stability of methods,and how to increase sensitivity and decrease detection limit.The researches for the determination of nitrite in food and sensitivity enhancement with cyclodextrins in this thesis included four aspects:(1) The fluorescence of o-phenylenediamine is very weak,but when it reacts with nitrite in an acidic medium,a strong fluorescence triazole- benzotriazole forms in alkaline medium.The sensitivity is largely enhanced in the presence of CD because of complexation,and the effect of HP-β-Cyclodextrin(HP-β-CD) was most effective.(2) A rapid,sensitive spectrophotometric determination of nitrite using new diazotizing and coupling reagents is described.The method is based on a diazotion-coupling reaction between benzidine and hydrochloric acid-naphthyl-ethylenediamine in a hydrochloric acid medium.This increase in absorbance is directly proportional to nitrite concentration obeying Beer's law.(3) A new fluorescence quenching method has been developed to determine nitrite in water and food samples.The method is based on the reaction between nitrite and the water-soluble dye phenosafranine(PS), which is used as an emission reagent,to form a non-fluorescent compound in hydrochloric acid.The sensitivity is largely enhanced in the presence of CD because of complexation.HP-β-CD was most effective.(4) A simple and sensitive spectrophotometric method for the determination of nitrite is described.The method is based on the oxidation of brilliant cresyl blue by nitrite in acidic solution,which resulted in the decrease in absorbance at 636 nm.The sensitivity is largely enhanced in the presence ofβ-CD because of inclusion complexation.