Guaiacol Catalytic Spectrophotometric Determination Of Trace Amounts Of Iron, Lead And Reaction Mechanism

It is well known that lack of iron or an exceeding amount of lead in one's body is very dangerous,especially,with the wide use of lead in industry and agriculture,people pay great attention to their poisonous effect on the environment.Therefore,there are an increasing importance in the research of the determination of them,within which,the most common methods are spectrophotometric techniques,atomic absorption spectrometry (AAS),oscillopolarography,inductively coupled plasma-atomic emission spectrometry (ICP-AES)and so on.But the methods listed above have their disadvantages:AAS needs expensive instruments;spectrophotography has poor sensitivity and its operations are very complex.Catalytic spectrophotometry,developed from common spectrophotography,having ideal sensitivity and not needing too expensive instruments,has become the most often used method in developing countries for the determination of trace metals.The research of catalytic spectrophotometry has become a hot point in the field of analytical chemistry.In the basis of retrieving science literatures and doing large amounts of experiments, the author of this dissertation found the ion of iron can facilitate the oxidation color reaction of guaiacol by potassium periodate and obtained a new method for the determineation of trace iron(Ⅲ):a catalytic spectrophotometric for the determination of iron with GA. Following experiments show that the ion of lead(Ⅱ)can facilitate the same color reaction in a more extent and catalytic spectrophotometric for the determination of trace lead(Ⅱ)with GA has also been developed.Our research in this dissertation include:finding the optimum reaction conditions such as the range of pH,the dosage of reactants,reaction time and temperature;plotting the calibration graph under the optimum conditions;testing the interference effects of ordinary ions;applying to determination of iron(Ⅲ)or lead(Ⅱ)in real samples by this proposed method;discussing the reaction mechanisms.The results of the experiments are:catalytic reaction for the determination of iron(Ⅲ) with GA should carry out in 1.5 mL potassium biphthalate-hydrochloric acid buffer solution(pH=2.6);the dosage of the oxidant-potassium periodate is 3 mL,the dosage of the surfactant-phen is 2 mL,the dosage of the indicator-GA is 0.6 mL;after reacting in 60℃constant temperature water bath for about 6 min,the absorbance of both catalyzed and uncatalyzed reaction mixtures should be tested in 480 nm.In the absence of surfactant,the regression equation of the calibration graph is△A=-0.01408+0.2472C_Fe(Ⅲ)with a correlation coefficient of r=0.9990.Iron(Ⅲ)concentration is linear for 0μg.(25mL)^-1-1.8μg·(25mL)^-1;In the presence of 2 mL 0.001 mol·L^-1surfactant phen,the regression equation is△A=0.1334+9.4073C_Fe(Ⅲ),with a correlation coefficient of r=0.9997.The ange of Fe(Ⅲ) is from 5ng·(25mL)^-1to 50ng·(25mL)^-1,and the detection limit is 2.21x10^-11g·mL^-1.The interference of copper(Ⅲ)could be masked by homocysteine.Catalytic spectrophotometric of the activated system has been used to determination of trace amount of iron(Ⅲ)in dianchi water,green lake,underground sewage in kunming,running water,mineral water, pure water and beer.The recoveries were 97.3%-102.3%.This system is a first-order reaction for Fe³⁺with apparent rate constant 3.15x10^-4s^-1and apparent activation energy 32.07 kJ.mol^-1.Catalytic reaction for the determination of lead(Ⅱ)with GA should carry out in 1.5mL hexamethylene tetramine-hydrochloric acid buffer solution(p=5.0);the dosage of the oxidant-potassium periodate is 4.5 mL,the dosage of the surfactant-tween20 is 3 mL, the dosage of the indicator-GA is 1 mL;after reacting in 70℃constant temperature water bath for about 18 min,the absorbance of both catalyzed and uncatalyzed reaction mixtures should be tested in 480 nm.The regression equation of the calibration graph is△A=2.8563+0.01272C_pb(Ⅱ),with a correlation coefficient of r=0.9996.Lead(Ⅱ) concentration is linear for 0μg.(25mL)^-1-22.5μg.(25mL)^-1,and the detection limit is 9.94x10g^-9g'mL^-1.Most of the foreign ions except for copper(Ⅱ),iron(Ⅲ)do not interfere with the determination.The interference of them can be removed by Ammonium fluoride and Thiourea.This method had been used to detect the concentration of lead(Ⅱ)in Peanuts, rice,potato slices expanded food,pu'er biluochun,pu'er maofeng,premium pu'er,jasmine tea,Yunnan red and Yunnan Green.The recoveries were 97.6%-103.7%.This system is a zero-order reaction for Pb²⁺.The apparent rate constant is 1.91x10^-4s^-1and the apparent activation energy is 10.61 kJ'mol^-1.