Liquid Phase Microextraction Coupled With GFAAS For Trace Elemental Analysis And Their Speciation

The toxicity and metabolic behavior of trace elements in organisms are not only related to their amount,but also depend on their existing forms/species.The accurate and sensitive analysis of trace elements and their species has been a hot issue for researchers in the field of analytical chemistry.Graphite furnace atomic absorption spectrometry（GFAAS）is a commonly used analytical technique for the analysis of trace elements and their species in environmental,biological and food samples,with the advantages of high sensitivity and good specificity.While,in real sample analysis by GFAAS detection,extremely low concentration of interest elements/species,complex sample matrix,and/or lacking of selectivity for specific species of a certain element,significantly hampers the quantification process.Before instrumental analysis,appropriate sample pretreatment techniques could help to achieve separation and preconcentration of target elements/species,resolving these problems mentioned above to some extent.Liquid phase microextraction（LPME）is a sample pretreatment technique with the advantages of simple and fast operation,low consumption of organic solvent and high enrichment factor.It has been widely used for trace analysis in environmental monitoring,food analysis and biomedicine fields.However,there are still some shortcomings in the development of LPME.In the analysis of trace elements and their species by LPME-involved methodologies,toxic organic solvents such as halogenated alkanes and methanol are usually used as the extraction solvents and dispersants,violating the concept of green chemistry;LPME systems suitable for the analysis of trace elemental species and metal-containing nanoparticles are relatively scarce,the application of LPME in the analysis of elemental species and nanoparticles needs further exploration.The aim of this dissertation is to develop new LPME systems based on green solvents and combine LPME with GFAAS for the analysis of trace elements and their species in environmental and biological samples,and to explore LPME system suitable for metal oxide nanoparticles analysis in environmental samples.The main contents are described as follows:（1）A method combining switchable hydrophilic solvents（SHSs）based LPME combined with GFAAS detection was established for the quantification of trace Pb（II）and Cd（II）analysis in environmental and biological samples.The SHS of protonated triethylamine carbonate（P-TEA-C）was synthesized and applied as the extractant,ammonium pyrrolidine dithiocarbamate（APDC）was chosen as the chelating reagent.Pb（II）and Cd（II）in APDC complex form was extracted into the triethylamine（TEA）phase by converting P-TEA-C into TEA.The factors affecting SHS-LPME extraction of Pb（II）and Cd（II）,such as sample pH,volume of SHS and NaOH,APDC concentration were investigated in detail.Under the optimal conditions,enrichment factor of 50 was achieved with consumption of 10 mL aqueous sample,and the limits of detection（LODs）of 16 and 3.9 ng L^-1 were obtained for Pb（II）and Cd（II）,respectively.The accuracy of the method was validated by the analysis of Certified Reference Materials（CRMs）of GBW07605（water）,GSBZ50009-88（tea）and GBW07601（GSH-1）（hair）.The method then was successfully applied for the analysis of trace Pb（II）and Cd（II）in environmental water,tea and human hair samples,with the recoveries of 94.9-110%.（2）A green switchable solvents based liquid phase microextraction（SHSs-LPME）method followed by GFAAS detection was proposed for the speciation of inorganic selenium in environmental water samples.The complex of Se（IV）with APDC was rapidly extracted into N,N-dimethylcyclohexylamine（DMCA）drops by adding sodium hydroxide solution,while Se（VI）was remained in the aqueous solutions.Based on it,the separation of Se（IV）and Se（VI）was realized.Total Se was determined by the proposed method after reduction of Se（VI）with the aid of 6 mol L^-1 HCl and 0.05 mol L^-1 KBr,and Se（VI）was calculated by subtracting Se（IV）from total Se.The factors affecting the microextraction procedure were studied systematically.Under the optimal conditions,the LODs of Se（IV）was 0.026 ng mL^-1with enrichment factor of 33-fold.The accuracy of the method was validated by the analysis of Certified Reference Materials（CRMs）of GSB 07-3172-2014（water）.The established method was applied to inorganic Se speciation in environmental water samples and the recoveries were 90.8-110%.（3）When the medium pH is higher than the isoelectric point(pH_PZC)of nanoparticles（NPs）,the surface of the NPs would be negatively charged,and the NPs can form a hydrophobic ion pair complex with cationic surfactant and thus be extracted into organic phase.Based on this,taking CuO NPs,NiO NPs and CoO NPs as target analytes,a new system of ion pairs based surfactant assisted dispersive liquid liquid microextraction（IP-SA-DLLME）was explored for the extraction of metal oxide NPs from environmental water,followed by GFAAS detection.Disodium ethylenediaminetetraacetate（EDTA）was chosen as the masking reagent for Cu（II）,Ni（II）,Co（II）ions,and the separation of CuO NPs,NiO NPs and CoO NPs from their corresponding metal cations was achieved.Under the optimal experimental conditions,the LODs of CuO NPs,NiO NPs and CoO NPs were 0.04,0.05 and 0.02μg L^-1,respectively,and the enrichment factors were 100-fold.The size and shape of CuO NPs,NiO NPs and CoO NPs was hardly affected by the extraction process,and the obtained organic phase can be directly introduced into GFAAS for detection without acid digestion.The application potential of the method was demonstrated by the analysis of CuO NPs,NiO NPs and CoO NPs with different size range in real water samples.