Study On Photochemical Formation Of Bromo Amino Acids In Aquatic Environment

The halogenated organics emitted by man-made production are not the only source of halogenated organics in the environment.Many natural processes can also produce halogenated organics.In natural waters,the photochemical reaction process is one of the important processes of organic transformation.In this dissertation,we selected the amino acids of small molecule nitrogenous organic compounds in water as the model compounds to form brominated amino acids by photochemical transformation in aqueous solution,and effects of some important aquatic environmental factors on this process are fully investigated the following works have been done:?1?The photochemical formation of brominated organic compounds was investigated in saline water under Hg lamp irradiation??>290 nm?,using tyrosine?Tyr?and histidine?His?as a model molecule.Only the photoreaction of Tyr to form the brominated product3-bromo-tyrosine.?3-BrTyr?and 3,5-dibromo-tyrosine?3,5-di BrTyr?.A solid phase extraction coupled with high performance liquid chromatography-triple quadrupole mass spectrometry?SPE-HPLC-MS/MS?method for the analysis of Tyr and two brominated products was established.The conditions of the final optimized instrument were as follows:Analysis of three targets in multi reaction monitoring?MRM?mode and positive mode of electrospray ionization source?ESI?,using 0.1%formic acid solution and acetonitrile?9:1?as the mobile phase.The linear correlation coefficient?R²?of 3 targets were 0.998,0.999 and0.999.The solid phase extraction?SPE?was used as the pre-treatment method in this study and optimized.The final pre-treatment conditions were using Clearnet-SCX column,sample pH 2.4,and 8 m L of 5%ammonia-methanol solution as eluent,the recoveries of the targets were 73.5%⁸3.1%,the relative standard deviations?n=3?were less than 5.25%,and the detection limits of the methods were all less than 4.72 ng/L,the recoveries of three targets in in Heishijiao Reef near Dalian were 72.7%⁸6.6%.?2?The photochemical formation of brominated organic compounds was investigated in saline water,using Tyrosine?Tyr?(C_0,Tyr=400?g/L)as a model molecule.Result shows that the bromide products 3-BrTyr and 3,5-diBrTyr were determined during the photo-transformation of Tyr in saline solution with Fe?III?at pH 3.0 under Hg lamp irradiation??>290 nm?.The degradation of Tyr,the amount of 3-BrTyr and 3,5-diBrTyr increased gradually with increase of Fe?III?concentrations.The effect of pH on the photochemical reaction of Tyr was also significant.The photodegradation rate of Tyr decreased with the increase of pH value in the range of p H 3.0⁸.0;the formation of 3-BrTyr and 3,5-diBrTyr decreased with the increase of p H.Under the same pH 8.0,the degradation rate of Tyr in natural seawater is far greater than that of simulated seawater,and the formation of 3-BrTyr and 3,5-diBr Tyr in natural seawater is significantly larger than that in simulated seawater.3,5-dimethylpyrazole?DMPZ?was used as a probe of non-radical active bromine species?HOBr,Br₂?during the photobromination reaction.The production of4-bromo-3,5-dimethylpyrazoles?BDMPZ?was measured by HPLC-MS/MS.It was concluded that HOBr and Br₂ are non-radical active bromine species.The number increases with increasing Fe?III?concentration and the bromination reaction increases.