Sample Pretreatment Combined With Inductively Coupled Plasma Mass Spectrometry To Analyze Trace Rare Earth Elements In Environmental Samples

In recent years,rare earth elements in seawater have been used as tracers for ocean or surface water complexation.At the same time,their content can provide important geochemical information and play an important role in geochemical research.On the other hand,the information of rare earth element concentration in crude oil can be used to understand the geological formation and exploitation process,provide information such as the source,maturity and type of crude oil,provide important information for the petroleum industry and geochemistry.Considering the amount of rare earth elements in seawater and crude oil is very low,high sensitive analysis technology that can provide multi-elements determination is needed.Since ICP-MS has excellent sensitivity and multi-element simultaneous analysis ability,it is currently one of the most important tools to detect rare earth ions in these complex matrix samples.However,the high salt matrix in seawater will accumulate on the sampling cone and may block the sampling cone hole;Crude oil samples contain complex organic matrix,which will carbonize and accumulate on the sampling cone during ICP-MS injection.These two kinds of problems will interfere with the direct injection detection of ICP-MS.Therefore,appropriate sample pretreatment is needed to separate the complex matrix of the sample and preconcentrate the rare earth elements in the samples.Therefore,the following research was carried out in this paper:(1)A coprecipitation method using zwitterionic compound zinc hydroxide as precipitant was established.Trace rare earth elements were effectively enriched and separated from seawater matrix.After rare earth ions were enriched by coprecipitation reaction,high concentration zinc ions were removed by KOH.The p H,precipitation time and the amount of precipitant affecting the extraction were optimized.Finally,the enriched rare earth elements were determined by ICP-MS.The accuracy of the method was verified by the quantitative analysis of rare earth elements in CASS-6.Compared with the conventional coprecipitation method,this method effectively realizes the separation of coprecipitation carrier reagent and target ions,which reduces the influence of high concentration carrier ions on the detection of trace rare earth ions.Finally,zinc hydroxide coprecipitation method was successfully applied to the separation and enrichment of rare earth elements in seawater samples.(2)A reversed-phase liquid-liquid microextraction method with switchable hydrophilic solvent N,N-dimethylformamide as capture agent and nitric acid as trigger was established to separate the matrix and enrich trace rare earth elements in crude oil.The N,N-dimethylformamide dissolve in oil sample and react with rare earth element ions in oil to produce hydrophobic complex;the hydrophobic rare earth element complex is converted into hydrophilic complex by nitric acid,and then back extracted into nitric acid phase,and then the extraction phase is taken for ICP-MS analysis.The type of capture agent,capture time,trigger reaction time and concentration of nitric acid were optimized.The accuracy of this method is verified by quantitative analysis and standard addition recovery experiment of rare earth elements in transformer oil samples.Finally,the method has been successfully applied to analyze the amount of rare earth elements in crude oil samples.Compared with the previous pretreatment methods for crude oil samples,this method has the characteristics of environmentfriendly,simple and fast operation,safety and efficiency.