Novel Separation Techniques For Elemental Speciation Analysis

In recent decades,heavy metal contamination to environment is of great concern because of the toxicities of heavy metals in relatively low concentrations and tendency towards bioaccumulation to plants,animals and human beings.The toxicological studies have indicated that the role and impact of a given element on the environment and living organisms depend primarily on its chemical form.Therefore,elemental speciation analysis is of great significance,and has become a hot and challenging research area.Inductively coupled plasma mass spectrometry(ICP-MS)has been proved to be the most powerful technique for the determination of trace elements in various matrices due to its attractive features:high sensitivity,wide linearity,multi-element capability,etc.Nevertheless,ICP-MS based quantification of metal species usually requires the application of a separation procedure prior to detection,because the element-specific techniques including ICP-MS cannot discriminate the species of a given element.The present work aims at investigating novel solid phase extraction(SPE),solid phase micro-extraction(SPME)and liquid chromatography techniques for trace elemental speciation analysis.Novel solid materials,on/off-line hyphenated system with ICP-MS,and chromatographic separation were developed.The major contents are described as follows:1.A sequential SPME system consisting of two monolithic capillary columns was developed for simultaneous separation and preconcentration of inorganic arsenic,followed by ICP-MS detection.The N-(?-aminoethyl)-?-aminopropyltriethoxysilane(AEAPTES)incorporated organic-inorganic hybrid monolithic column was employed as the extraction medium for SPME in this system.With the on-line design of dual columns and an oxidation coil,As(?)is quantitatively extracted by the first column,and As(III)in the effluent can be quantitatively extracted by the second column after oxidized to As(V)by a make-up KMnO4 solution.The retained As(V)or As(?)is then sequentially eluted by diluted HNO3 and introduced to ICP-MS for determination.The developed method was successfully applied to the speciation analysis of inorganic arsenic in drinking and environmental waters with satisfactory recoveries.2.A centrifugal microfluidic platform with multiple SPE units has been developed and successfully applied to separate Cr(?)and Cr(?)with high throughput,followed by ICP-MS detection.Monolithic capillary columns,prepared by polymerization of AEAPTES and TEOS,were integrated on a poly(dimethylsiloxane)(PDMS)chip and used as the mediums for the selective extraction of Cr(VI).The aqueous solutions on the chip were driven by centrifugal force produced by a centrifugal motor,so that high-throughput SPE was achieved by processing multiple samples simultaneously.The adsorption and elution conditions of Cr(?)onto the monolithic capillary column,and the rotation speed of the centrifugal motor were well studied.The feasibility of the proposed protocol was validated by certified reference materials and real water samples.The device possessing the advantages such as portability and simplicity provides a potential application for field sampling and pretreatment.3.A series of thiol-and amine-bifunctionalized mesoporous silicas were synthesized by one-pot co-condensation method.The mesoporous materials were systematically characterized.As(V)and As(?)were effectively adsorbed by amine and thiol on the functionalized silica,respectively,through electrostatic interaction and chelation.Adsorption isotherms and kinetic uptake profiles of As(?)and As(?)onto these adsorbents were investigated by batch adsorption experiments.On the other hand,this material was employed for speciation analysis of arsenic using a homemade syringe-based solid phase extraction device.The merits of easy preparation,low cost,high adsorption capacity and selective desorption,make the bifunctional mesoporous silica an ideal solid material for removal and speciation analysis of arsenic in environmental waters.4.A new magnetic solid phase extraction(MSPE)method using octyl-immobilized silica-coated magnetic Fe3O4(C8-Fe3O4@SiO2)nanoparticles as the MSPE absorbent combined with ICP-MS has been developed for speciation analysis of Sb(?)and Sb(?).Ammonium pyrrolidine dithiocarbamate(APDC)was employed as the chelating reagent.Sensitive speciation analysis of Sb(?)and Sb(?)could be achieved by selective SPE of either Sb(?)-APDC or Sb(total)-APDC complex under different pH on C8-Fe3O4@SiO2 nanoparticles.The experimental parameters,such as pH of solution,concentration of APDC,eluent type and sample volume were optimized in detail.This proposed method is simple,accurate and sensitive,and can be applied to the speciation of Sb(?)and Sb(?)in environmental waters without any pre-reduction or pre-oxidation operation.5.A high performance liquid chromatography on-line coupled with ICP-MS was employed for the determination of Cr(?)species in traditional Chinese medicines.The species were separated on an anion exchange column.The parameters of the mobile phase such as pH and concentration of NH4NO3 have been optimized to obtain lower retention times,better resolution and stronger peak intensity.The US EPA method 3060A,which is a test method for evaluating Cr(?)in solid materials,has been systematically studied using ICP-MS.It was demonstrated that there was a interconversion of Cr species in trace level in high temperature and large amount of alkaline.Therefore,a suitable modification was made to be used for extraction of Cr(?)in medicine samples.The analytical performance of the method was evaluated with a satisfactory result.