The Application Of Sample Pre-enrichment Techniques In Trace Elements Analysis

Trace elements have an important impact on ecosystems and biological organisms.Trace element analysis is critical for food safety control,environmental pollution monitoring,and human health assessment.Among many trace elements detection techniques,ICP-MS has proven to be the most effective means of elemental analysis due to its high sensitivity,wide linear range,and simultaneous multi-element analysis.However,there are some questions in the direct analysis of real samples by ICP-MS:（1）the content of the target element in real samples is lower than the detection limit of the instrument;（2）the complicated matrix of sample may seriously affect the accuracy of measurement results.In order to analyze ultra-trace elements in various samples,different sample pre-enrichment techniques were adopted to pre-concentrate the target metal ions or eliminate the interference of coexisting ions before ICP-MS measurement.The main research contents are introduced as follows:（1）A novel method of static electromembrane extraction–ICP-MS was established for the determination of ultra-trace rare earth elements in water.The effects of the position of electrodes,ionic strength in the donor phase,the stirring speed,the composition of supporting liquid membrane and acceptor phase,extraction voltage and time during the electromembrane extraction were studied.The optimal conditions were achieved:the anode platinum wire was placed at the bottom of the baker;1-octanol+3%v/v DEHP as SLM;40 mL aqueous samples without pH adjustment as DP;400μL of 5 mmol L^-1 HNO₃ as AP;extracting at 70 V for 60 min.Static electromembrane extraction can be successfully applied in large volume samples（40 mL of ultrapure water）,which may be due to the low electrical conductivity in ultrapure water resulting in a strong electric field within ultrapure water.The calibration of rare earth elements in the concentration range of 0.05/0.1⁵0 ng L^-1 exhibited excellent linearity with the correlation coefficient higher than 0.9980.The limits of detection（LOD）were between1.3²4 pg L^-1,and the enrichment factor ranged from 44 to 59.The concentrations of Y,La,Ce,Pr,Nd,Eu,Gd,Tb,Ho,Tm and Yb in ultrapure water ranged from 4.8 to 58.2pg L^-1,Sm,Dy,Er and Lu were not detected;The concentrations of Y,La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Ho,Er,Tm and Yb in pure distilled water ranged from 11.9 to 100.8pg L^-1,Dy and Lu were not detected.We believe that EME–ICP-MS can be used for ultra-trace element analysis in the future,and EME has proven to be a tool for purifying cations in water.（2）A novel poly（N-（4-vinyl）-benzyl iminodiacetic acid-divinylbenzene-N,N’-methylenebisacrylamide）capillary monolith was synthesised in situ.The structure and morphology were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy.Based on the capillary monolith,a method of capillary microextraction coupled with ICP-MS was established for the determination of Co and Cd in rice and human urine samples.The effects of the pH value of sample,sample flow rate,elution conditions and coexisting ions during capillary microextraction were studied,and the optimal conditions were achieved:the pH value of sample was 5;sample flow rate was 0.18 mL min^-1;50μL,0.5 mol L^-1 of HNO₃ as eluent and the flow rate was 25μL min^-1.The breakthrough curve test was used to evaluate the adsorption behavior of Co and Cd on the obtained capillary monolith.Dose-Response model was found to described well the breakthrough curves of Co and Cd at different initial concentrations（R²≥0.9844）.The adsorption capacity of the prepared capillary monolith for Co and Cd was 1541 and 1733μg m^-1 at an initial concentration of 2.5 mg L^-1,respectively.The capillary monolith has the advantages of large adsorption capacity,high extraction efficiency,wide pH tolerance range and simple preparation.The enrichment factor of the method was 100-folds with the sample volume was 5 mL.The calibration of Co and Cd in the concentration range of 0.005¹5μg L^-1 exhibited excellent linearity with the correlation coefficient were 0.9998 and 0.9999,and the LOD were 0.35 and 0.44 ng L^-1,respectively.The recoveries of Co and Cd in rice and human urine samples ranged from 89¹10%which proved that the method was suitable for the determination of trace Co and Cd in biological samples.