Assessment Of A Method For Total Organic Halogen Detection In Water Using Ultraviolet Photolysis Pretreatment

Halogenated organic compounds in water raise extensive concern in public due to their teratogencity,carcinogensis,and mutagenicity.Because of their diversity and complexity,halogenated compounds can't be readily measured as individual species.Total organic halogen(TOX)is proposed before as an alternative to evaluate the status of all halogenated compounds in water.Currently,the conventional method of measuring TOX usually applies pyrolysis process to convert halogenated organic compounds into inorganic halide,but there are a series of problems associated with it,such as the demand of high quality activated carbon,the oxidation of the bromide and iodide,the incomplete recovery of hadrogen halide gas,and the high costs of instruments and consuming items.In order to solve the above mentioned problems,we herein propose to apply vacuum ultraviolet(VUV)and ultraviolet(UV)systems to converst TOX into halides.Develop and optimize the ultraviolet conversion procedure.According to the dechlorination rate of monochloroacetic acid under different conditions,we ascertained the radiation time in VUV system was 60 min.Although 60 min is enough to dehalogen,elemental bromine and iodine can yield higher oxidation states,which would affect the determination via ion chromatography.Thus,this paper optimized the UV reduction condition of iodate due to higer oxidation degree compared to elemental bromine.And also,we evaluated the conversion of chloride and bromide ions under the favorable operating cond itions.There are three steps of the optimal operation procedure:i)photolysis of 60 min in VUV system;ii)adjustion p H ranging 10.5 to 11.5;and iii)photolysis of 30 min in UV system.Based on the optimal operation procedure,this paper studied the recovery of three standard compounds after all conversion steps.The results show that the recovery could reach 90% under p H value ranging from 10.5 to 11.5,meeting the requirement of this detection method.Common anions in water of 10 mg/L(Cl-,Br-,NO3-,and CO32-)has no impact on the recovery of standard compounds.Moreover,natural organic material with the concentration of 10 mg-C/L,such as humic acid,would not affect the recovery.In order to further evaluate this detection method,we conducted a series of experiments.The results shows that iodomethane,haloacetic acid,haloacetonitriles,halogen ethanol,halogenated acetaldehyde,and halogenated nitromethane could be measured accurately by this method.Under favorable operating conditions,this method has successfully achieved acceptable recoveries(> 92%)of halogenated organic compounds dosed to ultrapure and natural waters,a calibration curve with R2 > 0.9 for a wide range of concentrations from 0.01 to 1.00 mg/L.In addition,method detection limit of TOCl,TOBr,and TOI was 0.007 mg/L,0.011 mg/L,and 0.004 mg/L seprarately.