A New Detection Method For Total Organic Chlorine And Bromine Using Silver Carbonate Pretreatment

Disinfection byproducts(DBPs)are contaminants resulting from the reaction between disinfectants and natural organic matters.They cause potential hazardous effects on human health because of their high degree of carcinogenic ity.Dissolved organic halogen(DOX)is a collective parameter that indicates the sum of all DBPs,and its significance to DBPs studies cannot be ignored.Previously,DOX was measured with adsorption-pyrolysis method,but its loss of DBPs and high cost have affected its widespread application.To solve the problems,this paper intends to establish a new method for detecting DOX in water.The main process es includes the separation of DOX and inorganic halogen(DIX)followed by transformation of DOX into DIX.The main process of separation is based on a precipitation method by use of silver carbonate,and the process of transformation is based on UV photolysis.This method has the advantages of simple operation,rapid measurement and low cost,and therefore may have a broad application prospect.We use Cl-and Br-as the research objects during the exploration and optimization of the separation of DIX and DOX.The results showed that the silver carbonate precipitation method is an effective method to remove DIX.After adding silver carbonate,the precipitation in the solution was removed by 0.22 ?m microporous filter membrane,and finally,the residual Ag+ in the solution was removed by a hydrogen column.A new method for the determination of DOX in water was developed by combining the above optimized separation with the UV photolysis of DOX.Organic chloride and bromide were the research objects to evalua te the typical influencing factors of the method,including the effects of type and concentration of organic halides,effects of concentration of Cl-and Br-and the mixing systems.The results showed that under the optimized conditions of this experiment,the final recovery rates of 100 ?g/L~1 mg/L halogenated acetonitrile,100 ?g/L halogenated acids,halogenated methanes,and halogenated phenols were high,which were 85%~102%.The final recovery rates of halogenated acetaldehydes were low,which was about 60%.Cl-and Br-with initial concentrations of less than 100 mg/L had little effects on the detection results of this method.In most cases,the recovery rates of halogen in organic matter exceed 80%.The detection method was evaluated by using chloroacetonitrile and bromoacetonitrile as standard materials and total organic chlorine(TOCl)and total organic bromine(TOBr)as indexes respectively.The results showed that the correlation coefficients of the standard curves of TOCl and TOBr are greater than 0.999 using the measured values and theoretical values.The detection limits of TOCl and TOBr were about 8 ?g/L and 9 ?g/L.The difference between repeated test and theoretical value of TOCl and TOBr at different concentrations was less than 10%,and the relative standard deviation(RSD)of repeated test was no more than 7%.