Determination Of The Total Microcystins And Their Oxidative Degradation Study

Microcystins （MCs） are a group of cyanotoxins that happen most frequently, produce themost toxins and do much harm than any others in freshwater in the cyanobacteria bloom. MCscould enter the human body through multiple channels such as drinking, contacting pollutedwater, eating contaminated spires health food and through IV in special circumstances. MCswere dangerous potentially to people by cumulative amounts in fishes, entering the bodythrough aquatic products. In recent years, more than80kinds of MC had been found andthese toxins were similar to MC-LR. However, due to the constraints of the standard，both inChina and abroad, most studies concentrated on single MC and the researches about total MCwere limited actually. In order to fully reflect the MC pollution levels and ensure the safety ofdrinking water for humans and animals, rapid analysis and detection methods wereestablished for three kinds of environmental matrices by using GC/MS and LC-MS in thispaper, specific researches are as following:First of all, a method of sensitive determination of total MCs with GC/MS method usingmethylchloroformate as a derivatizing reagent was employed to detect the MCs in aqueoussolution. Water samples were concentrated through SPE. The oxidation of the MCs in watersample was achieved by adding the oxidant solution, which consists of0.025mol/L potassiumpermanganate and saturated sodium periodate. The pH of water sample was adjusted to9.0.The oxidation process needed1h to complete at25°C. The MMPB formed in the oxidationprocess was converted to methyl ester using methylchloroformate in the presence of pyridineas the catalyst and the derivatized product was then extracted by chloroform for thesubsequent analysis. The protonated molecules m/z146.1and91.0was selected in theselected ion monitoring mode for specific measurement. The results of showed the goodlinearities between peak area and analyte concentration in the range of2.5μg/L-1.010⁴μg/L and the limit of detection was0.56μg/L. The recoveries of the method were between84.0%-95.6%with the relative standard deviation （RSD） between4.3%-6.1%（n=3） bydetecting15water samples. The results reflect the method apply to the detection of total MCin aqueous solution.On the basis of the above work, we further explore the feasibility of the application ofthe method on detecting total MCs in the sediments. A method for determination of total MCswith GC/MS method was employed to detect the MCs in sediments. Samples were extractedby5%HAc and methanol before centrifugation. The supernate was separated and enriched bySPE. The oxidation of the MCs was achieved by adding the oxidant solution, which consistsof0.025mol/L potassium permanganate and saturated sodium periodate after the pH ofsediment samples was adjusted to9.0. The oxidized derivative was converted to methyl ester using methylchloroformate before the GC/MS analysis. The limit of detection was as low as7.0μg/g and the recoveries for spiked samples between82.0%-98.6%with the RSD between3.9%-6.7%（n=3）. The results reflect the method apply to the detection of total MC insediments.Secondly, in order to simplify the operation of determination of total MCs, we studiedthe new method without methyl ester by liquid chromatography tandem mass spectrometry.We quantify the total MCs in cyanobacterial hepatotoxins by determination of MMPB withultra-high performance liquid chromatography mass spectrometry （UPLC-Q-TOF-MS）.Samples were extracted by50%HAc and methanol before centrifugation. The supernate wasseparated and enriched by SPE after concentration. The separation was performed on a BEHC₁₈column with gradient elutions. The oxidation of the MCs was achieved by adding theoxidant solution, which consists of0.050mol/L potassium permanganate and saturatedsodium periodate after the pH of samples was adjusted to9.0. The protonated molecules m/z131.10was selected in the selected ion monitoring mode for specific measurement. Theresults of showed the good linearities between peak area and analyte concentration in therange of30.0μg/L–2000μg/L and the limit of detection was as low as0.8μg/L. Therecoveries of the method were in the range of82.0%-98.6%and the RSD of2.7%-6.7%（n=3）. The results reflect the method apply to determine total cyanobacterial hepatotoxins MCs.In this paper, a new oxidant1,3-dibromo-5,5-dimethylhydantoin（DBDMH）was studiedas a possible approach for the removal of MCs. MC-RR which is the most abundant in TaiLake was employed as the model compounds. The optimum reaction conditions:5min wasselected as the reaction time, the degradation efficiency was decreased with increase of pH,20mg/L was selected as the optimum initial concentration. The result showed the degradationreaction followed the first-order kinetics. Through the mass spectrum analysis to determinethe relative molecular mass and its degradation products, we further discussed its chemicaldegradation pathway in the paper.