Study On Rapid Determination Of Total Mercury And Methyl Mercury In Fish

Mercury(Hg)is a common heavy metal element,generally in the form of metallic mercury,inorganic mercury and organic mercury,and is one of the most important inorganic pollutants in the current environment and food.Among all kinds of elemental forms of mercury,methoxymercury is the most toxic form of mercury,which has adverse effects on cardiovascular and cerebrovascular system,nervous system,reproductive system and immune system,especially neurotoxicity.What's more,methylmercury accumulates at the top of the food chain,and fish is one of the biggest food sources of methylmercury.Therefore,it is particularly important to monitor the total mercury and methyl mercury in fish samples.At present,the laboratory testing method on morphology of total mercury in food requires complicated sample preparation process,consumes large amounts of chemical reagent and time.It easily causes the loss of the trace elemental mercury.Besides,the mercury speciation analysis also need to be complicated with expensive chromatography atomic spectrum combination instrument system.It is difficult to the laboratory application promotion in a line.Therefore,aiming at the demand of simple and rapid analysis of total mercury and methyl mercury in fish,this study established a method of direct sampling detection of total mercury in fish.And based on catalytic pyrolysis of gold amalgam atomic absorption spectrometry.In addition,the principle of reduction reaction of stannous chloride was innovatively applied to the analysis of mercury morphology,and a rapid method for the determination of organic mercury in fish was established by catalytic pyrolysis and amalgam atomic absorption method.In this study,the rapid and accurate analysis of total mercury and organic mercury was achieved through simple sample processing and the use of catalytic pyrolysis amalgam atomic absorption device,which has the characteristics of convenience,efficiency and environmental protection.It is especially suitable for the rapid detection of mercury forms in grassroots laboratories.The main research contents and relevant results of this paper are as follows:1.Determination of total mercury in fish.Firstly,the optimization test of the drying pyrolysis time and the heating time of the gold trap was carried out on the mercury measuring instrument.Finally,the instrument conditions were determined as the pyrolysis time of 60 s and the release time of the gold trap of 12 s.Methodological evaluation result shows that:of the total mercury in fish method detection limit(LOD)is 0.3?g/kg,quantitative limit(LOQ),0.9?g/kg,long course(low concentration)standard curve of the linear range of 0~20 ng,short course(high concentration)the linear range of 20 ng~500 ng,standard curve R~2>0.998,the days of relative standard deviation(RSD)<5%(n=4),daytime RSD<8%(n=4).The standard recovery rates of various fish samples ranged from 93%to 110%,and the determination results of matrix standard substances(NIST1566b)of aquatic animal samples were all within the uncertainty range.This method does not require sample digestion,and the analysis time from weighing the sample to obtaining the determination result can be controlled within5 min.2.Determination of methyl mercury in fish.Based on the catalytic pyrolysis of gold amalgam atomic absorption mercury measuring instrument can only determine the content of mercury in the sample,unable to distinguish the form of mercury,so the determination of the content of methyl mercury in the sample needs a step of pre-treatment,that is,through the reduction reaction of tin chloride,the inorganic mercury in the sample is reduced,leaving only methyl mercury to be tested on the machine.The extraction method of methyl mercury in fish was to take 0.5 g fish samples,put them into a 15 mL centrifuge tube,add 10 mL 5 mol/L hydrochloric acid solution,and leave overnight.Ultrasonic water bath was performed for 60 min at room temperature,during which vibration was performed several times.Centrifuge at8000r/min under 4?for 15 min.Complete vapor generation of inorganic mercury can be achieved by adding 1 mL 10%stannous chloride solution to the fish sample.It is generally believed that organic mercury in food exists in the form of methyl mercury,so the inorganic mercury in the sample is reduced,leaving only methyl mercury.Using the principle of reducing inorganic mercury with stannous chloride,the treated samples were detected with a mercury detector to determine the content of methyl mercury in the samples.The methodology of the method is evaluated.Methods:the detection limit(LOD)was 1.2?g/kg,the quantitative limit(LOQ)was 3.6?g/kg,the linear range of standard curve of long pool(low concentration)was 0~20 ng,the linear range of short pool(high concentration)was 20~500 ng,the standard curve R~2>0.998,intraday RSD<7%(n=4),daytime RSD<9%(n=4),and the standard recovery rate was between 85%~106%.Compared with the LC-AFS method in GB 5009.17"determination of total mercury and organic mercury in national standard food for food safety",the relative difference between the two groups of data was<5.7%,showing a small difference between the two groups of data,indicating that this research method can accurately determine the content of methyl mercury in fish samples.