Determination Of Alkyl Mercury In Water By Liquid Chromatography With Atomic Fluorescence Spectrometry

According to the relevant state document requirements,the "Water quality-determination of alkyl mercury-liquid chromatography / atomic fluorescence spectrometry detection" had been included in the 2016 annual environmental standard revision project which uniform number is 2016-16.In this paper,liquid chromatography combined with atomic fluorescence spectrometry(LC-AFS)method was proposed to detect methyl mercury and ethyl mercury in environmental water samples.The main work and conclusions are as follows:Firstly,the parameters of LC-AFS were optimized and conditions are as follows: C18 column has better separation effect,the mobile phase consists of 5%CH3OH,1.2g/L L-cysteine and 4.62g/L CH3COONH4,flow rate is 1.0mL/min;oxidizing agents: 0.2% K2S2O8+0.5% KOH;carrying agents: 5% HCl;reducing agents:0.2% KBH4 +0.5% KOH.Lamp current is 30 mA,negative high voltage is 300 V,flow rate of Ar carrier gas and shielding gas: 300 and 1000 mL/min.Under the optimized conditions,the linear ranges for methyl mercury and ethyl mercury were between(0.1~10)ng/L,with correlative coefficients more than 0.9990.Secondly,the water samples were extracted by liquid-liquid extraction and solid-phase extraction(SPE),and the recovery rate was calculated after measuring by LC-AFS.The recovery rate of methyl mercury and ethyl mercury with liquid-liquid extraction varied from 76%~114% for low,medium and high three concentrations.The relative standard deviations(n=6)was between 4.1% to 7.4%.Three types of SPE methods were used in the experiment: homemade sulfhydryl cotton,C18 SPE disk andC18 SPE cartridge.Corresponding to low,medium and high concentrations,the recovery rate of methyl mercury with sulfhydryl cotton is 103%?96.0%?65.8%,and ethyl mercury is 96.3%?54.6%?23.0%,the recovery rate is not stable.The recovery rate of methyl mercury and ethyl mercury with C18 SPE disk varied from 34.4% to57.4%.The recovery rate of methyl mercury and ethyl mercury with C18 SPE cartridge varied from 55.4% to 73.1%.Liquid-liquid extraction is the best method by comparing the recovery rate,method detection limit,ease to operate,cost and other factors.Thirdly,liquid-liquid extraction combined with LC-AFS was used to detect actual water samples and the recovery rate.Actual water samples include tap water,reservoir samples and outlet samples of wastewater treatment plants.There are no methyl mercury and ethyl mercury in tap water and reservoir water.The concentration of methyl mercury was 0.29 ng/L in Tuandao wastewater treatment plant,and 0.11ng/L in Loushan river wastewater treatment plant.The results showed that the quality of water sample from wastewater treatment plants could reach the standard?Integrated Wastewater Discharge Standard?,and the overall recovery rate varied from 74.0% to 116.7%.The outcome could meet the requirements for the analysis of methyl mercury and ethyl mercury.The analysis method of methyl mercury and ethyl mercury in water samples has been established through improving the disadvantages of existing method.It can reduce the matrix interference and method detection limit,and improve the precision,accuracy and repeatability.By detecting actual water samples with this method,method basis for the analyze,pollution control work and the revision of relevant standards of methyl mercury and ethyl mercury in water were provided.