Study On The Analysisl Methods Of Fluoride In Soil Environment

As a common element of environmental chemistry and life science research,fluorine has the highest electronegativity amaong known elements and very lively chemical properties.Therefore,it could be reacted with all metals and the majority of non-metal directly to form fluoride compounds.Thus,fluoride in the environment,which meant the binary compounds containing fluorine with oxidation state of minus one valence,was only present as fluorine anion.Fluoride could have complex forms in soil,and the water soluble fluorine and exchangeable fluoride have high efficiency for plants,animals,microorganisms and humans.Fluorine pollution in the environment mainly came from the industrial waste and the natural geological process of fluorine enrichment in the local areas.Fluoride is an important component of all mineralized tissues in human.The intake of proper amount of:fluoride is beneficial to the growth of bones and teeth,but excessive intake would cause fluorine poisoning,with symptoms like spot glair tooth,and fluorosis when the situation becomes serious.Endemic fluorosis is a typical geochemical disease,which has a wide distribution and causes serious harm across our country.International organizations and countries around the have taken measures to effectively control fluoride in water,soil,air and other media.Therefore,systematic study on the method for the determination of fluoride in soil,is conducive to accurately grasp the transition of the fluoride in the environment in time,which can promote the effective treatment of fluorine pollution in environment soi,1 and is of great value to practical application.The thesis focused on the establishment of a method for the determination of water soluble fluoride and total fluoride in soil,including the pretreatment method and analysis conditions of ion-selective electrode method.The quality control and quality assurance technical indexes of the method were verified by 22 actual soil samples and 10 certified soil standard samples.The method was proved to have good practicability through six laboratories.The main research results were listed in the following.First,the pretreatment methods of water soluble fluoride and total fluoride in soil were studied.The leaching conditions were determined through three levels of certified soil standard samples of different solid/liquid ratio by comparing to different extraction conditions,leaching time and temperatures.For total fluoride in soil,similar experiments were performed by comparing to factors including alkali and soil ratios,temperatures and time controls to determine leaching conditions.Second,Certified standard samples were repeatedly compared by ion-selective electrode method with buffer solutions having different total ionic strength.It was found that 1 mol/L sodium citrate was better buffer capacity among different ionic buffers.In addition,critical interference concentrations of calcium ions,magnesium ions,iron ions and aluminum ions were determined by adding the metal ions to the 1.0 mg/L fluoride standard samples.At the same time,the standard curve in the test range and the blank level were determined according to the existing equipment and reagent conditions.Finally,the technical requirements of quality control and quality assurance wereprovided.Third,the method for determining fluoride in soil was established using ion-selective electrode.Electrode potential response as a function of logarithm of content was showed good linear relationship when the fluoride content range was from 5?g to 500?g.The correlation R was equal to or larger than 0.9992,with good reproducibility of the relative standard deviation which it was less than 10%,and the recovery rates from 70.0%to 120%.By calculation,the method detection limit was 2.5?g.When the sample size was 5.0 g,the detection limit was 0.5 mg/kg for the determination of water soluble fluoride in soil and the minimum quantitative limit was 2.0 mg/kg.When the sample was 0.2 g,the detection limit was 13 mg/kg for the determination of total fluoride in soil and the minimum quantitative limit was 50 mg/kg.Finally,it was proved that the method was accurate and efficient.It could be applied to the determination of fluoride in soil of different areas and functional areas.