Novel Liquid Phase Microextraction Techniques And Their Application In Trace/ultra-trace Elements And Speciation Analysis

It is well known that the toxicity and bio-availability of a specific element is highly dependent on its total content and physicochemical forms in environmental and biological samples. Therefore, it is significant to develop methods for trace/ultra-trace elements and their speciation analysis. Since inductively coupled plasma mass spectrometry (ICP-MS) has many merits of high sensitivity, wide dynamic linear range, multi-element detection and isotope analysis ability, it is one of the most powerful techniques for trace/ultra-trace elements and their speciation analysis. Nevertheless, direct analysis of trace/ultra-trace elements and their speciation by ICP-MS is still a difficult task, because not only of the extremely low concentration of target analytes in real samples, but also the spectroscopic and non-spectroscopic interferences resulted from the complicated sample matrix seriously affected the accuracy of the analytical results. To resolve such problems and improve the analytical performance, efficient sample pretreatment techniques for separation and preconcentration of target elements and their species prior to ICP-MS analysis is frequently required. In recent years, various novel miniaturized sample pretreatment techniques, such as fiber-solid phase microextraction (fiber-SPME), capillary microextraction (CME), stir bar sorptive extraction (SBSE), magnetic solid phase extraction (MSPE) and liquid phase microextraction (LPME), have been developed and widely applied for trace analytes analysis. Among them, LPME is simple, fast, low cost and has been widely employed for trace analytes analysis in environmental, biological and food samples with high enrichment factors (EFs). However, the application of LPME in trace/ultra-trace elements especially speciation analysis is limited due to the lack of suitable extraction system, and each mode of LPME has its own drawbacks, such as the instability of solvent drop in single drop microextraction, the relatively long extraction time of hollow fiber liquid phase microextraction (HF-LPME), the limited applicable organic solvent for dispersive liquid liquid microextraction (DLLME) and solidified floating organic drop microextraction (SFODME), etc. The aim of this dissertation is to explore novel LPME techniques for trace/ultra-trace elements and their speciation analysis; to develop LPME-based dual extraction techniques and combine them with electrothermal vaporization/high performance liquid chromatography-inductively coupled plasma mass spectrometry (ETV/HPLC-ICP-MS) for elements and their speciation analysis in environmental and biological samples. The major contents of this dissertation are described as follows:(1) A new method of SFODME combined with ETV-ICP-MS was developed for the determination of trace heavy metals in environmental water samples with sodium diethyldithiocarbamate (DDTC) as both chelating reagent in SFODME and chemical modifier in ETV. The factors affecting the microextraction efficiency were studied in detail and the optimization of extraction conditions was established. Under the optimal conditions, the limits of detection (LODs) for SFODME-ETV-ICP-MS determination of Co, Pd, Cd, Hg, Pb and Bi were found to be0.0060,0.0091,0.0020,0.0041,0.0170and0.0041ng mL-1, respectively, with the relative standard deviations (RSDs) of2.8-10.0%(c=0.5ng mL-1, n=7). The developed method was successfully applied to the analysis of six target metals in Yangtze River and East Lake water samples with recoveries ranging from77.7to119.1%. To validate the accuracy of the method, a certified reference material of Environmental Water (GSBZ50009-88) was analyzed and the determined values were in good agreement with the certified values.(2) A new method of phase transfer (PT)-HF-LPME combined with ETV-ICP-MS has been developed for the determination of trace Co, Pd, Cd and Bi in environmental and biological samples. In PT-HF-LPME, an intermediate solvent (1-butanol) was added into the sample solution to ensure the maximum contact area between the target metal ions and the chelating reagent (8-hydroxyquinoline,8-HQ), which accelerated the formation of8-HQ-metal complexes and their subsequent extraction by extraction solvent (toluene). The experimental parameters affecting the extraction efficiency of PT-HF-LPME for the target metals were studied. Under the optimized conditions, the EFs for Co, Pd, Cd and Bi were110,393,121and111-fold, respectively, and the LODs ranged from3.7to8.3ng L-1. The RSDs (c=0.5ng mL-1, n=7) were8.7,6.2, 12.4and12.9%for Co, Pd, Cd and Bi, respectively. To validate the accuracy of the proposed method, two certified reference materials of GSBZ50009-88Environmental Water and GBW09103Human Urine were analyzed, and the results obtained for Cd were in good agreement with the certified values. Finally, the developed method was successfully applied to the analysis of Co, Pd, Cd and Bi in lake water and human urine samples.(3) A simple and efficient two-step method of dispersive solid phase extraction (D-SPE) followed by DLLME combined with ETV-ICP-MS has been developed for the determination of15target rare earth elements (REEs) in environmental water and sediment samples. With Chelex100as the adsorbent of D-SPE, the target REEs were firstly extracted and then desorbed by0.1mol L-1HNO3. After addition of125mmol L-1tris and40mmol L-11-phenyl-3-methyl-4-benzoylpyrazolone (PMBP), the target REEs were further preconcentrated into CCl4by DLLME. Various parameters affecting the extraction of target REEs by D-SPE and DLLME were investigated in detail. Under the optimal conditions, the LODs for target REEs were in the range of0.003-0.073ng L-1with the RSDs (CY,La,Ce,Pr,Nd,Gd,Dy=1.0ng L-1, CSm,Eu,Tb,Ho,Er,Tm,Yb, Lu=0.2ng L-1, n=7) ranging from6.7to11.5%, and the EFs varied from234to566-fold. To validate the accuracy of the proposed method, the certified reference material of Stream sediment GBW07301a was analyzed, and determined values of target REEs were in good agreement with the certified values. Finally, the proposed method of D-SPE-DLLME-ETV-ICP-MS was successfully applied to the determination of15REEs in real water and sediment samples with the recoveries of78-115%and75-117%for the spiked water and sediment samples, respectively.(4) A novel method of ionic liquid based carrier mediated hollow fiber liquid liquid liquid microextraction (IL-carrier mediated HF-LLLME) combined with HPLC-ICP-MS has been developed for the speciation of five phenylarsenic compounds and arsenate in chicken and feed samples. The target arsenic species were extracted from6mL aqueous samples (pH=10.2) into an organic phase (20%(v/v)[MTOA]+[Cl]-in toluene) impregnated in the pores of a hollow fiber, then back extracted into10μL acceptor phase of0.3mol L-1NaBr in the lumen of the hollow fiber. The main driving force for the extraction was the gradient concentration of counter ion from the donor phase to the acceptor phase. Factors affecting the extraction of target arsenic species were investigated in detail. Under the optimal conditions, the LODs for five target phenylarsenic compounds and arsenate were in the range of1.4-16ng L-1with the RSDs (cAs(v),4-OH,3-NHPAA,PA,4-NPAA=0.05μg L-1, cp-ASA=0.10μg L-1, n=7) ranging from3.6to10.0%, and the EFs varing from86to372-fold. The proposed IL-carrier mediated HF-LLLME-HPLC-ICP-MS method was successfully applied to the determination of five phenylarsenic compounds and arsenate in chicken and feed samples with the recoveries for the corresponding spiked samples in the range of79.2-105.4%and81.1-117.8%, respectively.(5) A new method of magnetic solid phase extraction (MSPE) combined with hollow fiber liquid liquid liquid microextraction (HF-LLLME) for the extraction of selenoamino acids and the subsequent determination by HPLC-ICP-MS has been developed. Graphene oxide (GO) modified magnetic nanoparticles (Fe3O4@GO MNPs) has been prepared, and Cu2+was adsorbed onto the surface of the prepared Fe3O4@GO MNPs for the adsorption of target seleno amino acids based on the interaction between Cu2+and seleno amino acids. Aqueous ethylenediamine was employed as desorption solvent, and the desorption solution was directly employed as the donor solution in the subsequent HF-LLLME procedure for further extraction of target seleno amino acids. In HF-LLLME,1-octanol was employed as extraction solvent, ionic liquid trioctylmethylammonium chloride ([MTOA]+[Cl]-) was employed as carrier for the extraction of target seleno amino acids, and aqueous NaNO3solution was employed as acceptor solution. The target seleno amino acids were extracted from the donor solution into the organic phase and then back into the acceptor solution under the driving force of ion-pair formation between target seleno amino acids and [MTOA]+[Cl]-and the gradient counter ions between donor phase and the acceptor phase. Various factors influencing the extraction of target seleno amino acids by MSPE and HF-LLLME was investigated thoroughly, and the analytical performance of the proposed method was studied under the optimized extraction conditions. After preconcentration by MSPE-HF-LLLME, the EFs for target seleno amino acids ranged from152to278-fold, and the LODs for target seleno amino acids by the proposed MSPE-HF-LLLME-HPLC-ICP-MS was in the range of 0.0075-0.013μg L-1. A certified reference material of SELM-1was used to validate the accuracy of the proposed method, and the determined value of SeMet was in good agreement with the certified values. The proposed method was successfully applied to the speciation of seleno amino acids in rice and Se-enriched yeast cell samples.