| Due to their special electronic structural characteristics and unique physical and chemical properties,rare earth elements(REEs)have an irreplaceable role in many fields.They have been widely used in the fields of catalysis,superconductors,elec-tronic products,chemical sensors,hybrid electric vehicles,fertilizer and so on.However,with the widespread application of REEs not only increases their con-sumption but also releases them into the environment,which can enter the human body via the food chain and then influences the human body.Meanwhile,REEs have been listed as "New and Emerging Risks to Occupational Safety and Health"by the European Agency for Safety and Health at Work.Therefore,the development of sensitive and feasible methods for determination of trace REEs in environmental samples can be provide support to the assessment of environmental pollution,and is of great significance to the study of toxicity and toxicology in animals and plants.However,the low concentration of REEs in environmental samples and contains a large amount of other elements,which often interfere with the enrichment,recovery,and detection of REEs.Therefore,it is necessary to develop a fast and efficient preconcentration method for the detection and recovery of trace REEs in a complex sample matrix.Based on this,the environmental friendly N,N,N’,N’-tetraoctyl diglycolamide(TODGA)was selected as an extractant to extract REEs from envi-ronmental samples with complex matrix,and combined with inductively coupled plasma optical emission spectrometry(ICP-OES)to establish the preconcentration,separation and detection method of trace REEs in environmental samples.Mean-while,we propose to graft diglycolamide(DGA)derivatives onto a polydopamine(PDA)modified Fe3O4 solid surface,and synthesize a novel magnetic nanomaterial Fe3O4@PDA@DGA as an alternative material for the separation and enrichment of REEs.And a novel method of Magnetic solid phase extraction(MSPE)-ICP-OES was developed for the preconcentration,separation and determination of REEs.The research results are presented as follows:(1)An analytical method for the simultaneous determination of 16 trace REEs in water samples by liquid-liquid extraction(LLE)coupled with inductively cou-pled plasma optical emission spectrometry(ICP-OES)was established.With this method,TODGA was used as the extractant to perform the LLE sample pretreat-ment procedure.All 16 REEs were extracted from a 3 mol L-1 nitric acid medium into an organic phase by a 0.025 mol L-1 TODGA petroleum ether solution.A 0.03 mol L-1 ethylenediaminetetraacetic acid disodium salt(EDTA)solution was used for back-extraction to strip the REEs from the organic phase into the aqueous phase,and then detected by ICP-OES.Under the optimum experimental conditions,the limits of detection for the REEs ranged from 0.0405 μg L-1(Nd)to 0.504μg L-1(Ho).The relative standard deviations(c=100μg L-1,n＝7)were from 0.5%(Eu)to 4.0%(Tm)with a linear range of 4-1000μg L-1(R2>0.999).The recoveries of 16 REEs ranged from 95.9%to 106%.The LLE-ICP-OES method established in this study has the advantages of simple operation,low detection limits,fast analysis speed and the ability to simultaneously determine 16 REEs,thereby acting as a vi-able alternative for the simultaneous detection of trace amounts of REEs in water samples.(2)A novel method was developed for the determination of trace REEs in fruit samples by microwave digestion coupled with ICP-OES after preconcentration with TODGA.The parameters affecting the extraction and back-extraction behaviors of the target analytes in LLE were studied systematically.Under the optimum condi-tions,the limits of detection for the target REEs of interest were in the range of 0.0548(Tb)-0.541(La)μg L-1,and the tolerable concentration ratios were reaches 4 orders of magnitude for the common interfering ions.The relative standard devi-ations(c= 100 μg L-1,n=7)were from 0.6%(Sm)to 3.3%(La)with the wide linear range spanned three orders of magnitude(R2>0.999).The recoveries for the spiked fruit samples were ranged from 92.1%to 104%.The proposed method has the advantages of simple operation,good anti-interference ability,simultaneous de-termine 16 REEs,which has been successfully applied for analysis of REEs in the 10 locally collected fruit samples,thereby exhibits application potential for the analysis of trace REEs in biological samples with complex matrix.(3)In this work,a novel method for magnetic solid phase extraction(MSPE)coupled with ICP-OES was developed,which can quantitatively determine trace REEs in environmental water.The magnetic nanomaterials were synthesized by grafting diglycolamide(DGA)derivatives onto polydopamine(PDA)functional-ized magnetic nanomaterials(Fe3O4@PDA@DGA).The adsorption behaviors of Fe3O4@PDA@DGA for rare earth elements(REEs)were evaluated.The character-ization results indicated that the Fe3O4 nanoparticles form a hexagonal-like two-dimensional projection shape,and DGA is successfully grafted onto the surface of the nanomaterials.With the MSPE procedure,the parameters affecting the adsorp-tion behaviors of the REEs on Fe3O4@PDA@DGA nanomaterials,such as pH,ul-trasonic adsorption time,mass and solution volume were investigated systemati-cally.Under the optimum experimental conditions,the limits of detections and the relative standard deviations(RSDs)of 16 REEs(C= 10μg L-1,n=7)were in the range of 0.039μg L-1 for Eu to 0.425μg L-1 for Nd and 1%for La to 3.9%for Gd.The linear range of the calibration curve over 2-1000 μg L-1(R2>0.999)was ob-tained for the target analytes.This developed method was applied for the environ-mental samples and the recoveries were 95.8-1 05%for the spiked water.The pro-posed MSPE-ICP-OES method has the advantages of easy separation,simple oper-ation,good anti-interference capability,fast adsorption and elution kinetics,low detection limits,high sensitivity and fast analysis speed,thereby acting as a poten-tial application for the simultaneous analysis of trace REEs in environmental sam-ples.(4)The extraction mechanism of the extractant in this work was investigated by density functional theory,the extraction procedure and the structure of the com-plex after extraction were determined.The specific selectivity of extractant to REEs was determined by calculating the change of zero-point energy in the extraction procedure.In addition,it was confirmed that the final complex was RE(DGA)(NO3)3 with octahedral structure.Furthermore,the coordination ability of carbonyl oxygen atoms in the extractant was stronger than that of ester oxygen atoms.The theoretical calculation proves that the extractant has good selectivity and anti-interference characteristics. |
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