Application Of Micro-liquid Extraction-atomic Spectrometry In Elemental Speciation Analysis

It is well known that the physiochemical properties, bioavailability, mobility, and transformation of an element depend to a great extent upon its chemical species present and concentration in nature. Therefore, speciation analysis of the element is more significant than determining its total level. Atomic spectroscopy is an important tool for analyzing trace elements. However, it only obtains total amount of trace elements, and can not discriminate elemental species. Hence, atomic spectrometry combined with a suitable separation and/or preconcentration procedure is considered as an effective technique for the speciation analysis. Liquid phase extraction is one of common methods used for separating or/and concentrating elemental species. Liquid phase microextraction (LPME) and cloud point extraction (CPE) are new kinds of miniaturized liquid phase extraction, which offer such advantages like simplicity, reduced cost, safety, achievement of high enrichment factor, and easy hyphenation of other apparatuses. Miniaturized liquid phase extraction in combination with atomic spectroscopy has demonstrated more potential in specation analysis of trace or ultra-trace elements.The objective of this work aims to develop new methods for specation analysis of elements in water and tea samples by the combination of miniaturized liquid phase extraction with atomic spectroscopy. The major contents are summarized as follows:(1) A facile directly suspended droplet microextraction (DSDME) coupled to electrothermal atomic absorption spectrometry (ETAAS) was developed for the specation of Cr(?) and Cr(?) in environmental water samples. Diverse variables affecting DSDME, such as pH, extraction sovent and its volume,8-hydroxyquinoline concentration, extraction temperature, stirring rate, and extraction time, were detailedly studied. Under the optimum condtions, the limit of dection (3?, LOD) and the relative standard deviation (RSD) for Cr(?) were0.03ng mL-1and4.7%(C=1.0ng mL-1, n=5), respectively. A linear calibration range of0.10-2.0ng mL-1was obtained by the proposed method. This method was successfully applied for analyzing Cr(?) and Cr(?) in well water and tap water samples with spiking recoveries in the range of90.0%-110.0%for Cr(?) and93.3%-114.0%for Cr(VI).(2) A simple method for the speciation of Cr(?)/Cr(?) by flame atomic absorption spectrometry (FAAS) after room temperature ionic liquid (1-octyl-3-methylimidazolium hexafluorophosophate,[C8MIM][PF6])-based dispersive liquid-liquid microextraction (DLLME) was presented. Cr(?) and total chromium (Cr(?) and Cr(?)) could be extracted by [C8MIM][PF6] at the pH value of5.0and6.5, respectively. Cr(?) content was obtained by subtracting Cr(?) from the total chromium. Different main factors of DLLME were evaluated. Under the selected conditions, the limits of dection (3?) for Cr(?) and Cr(?) were1.0ng mL-1and0.41ng mL-1. The RSDs for Cr(?) and Cr(?) were3.3%and4.0%(C=80.0ng mL-1, n=5), respectively. The calibration curves exhibited linearity over the concentration range of5.0-200ng mL-1for Cr(?) and3.0-800ng mL-1for Cr(?). The present method was successfully applied for the derermination of Cr(?) and Cr(?) in tap, purified, and lake water samples, and the recoveries were91.3%-108.6%for Cr(?) and91.2%-108.0%for Cr(?).(3) A rapid method based on DLLME with room temperature ionic liquid1,3-dibutylimidazolium hexafluorophosophate ([BBIM][PF6]) coupled to FAAS was developed for the speciation of Mn(?)/Mn(?) in tea samples. Several factors affecting DLLME were investigated in detail. Mn(?) and total manganese (Mn(?)+Mn(?)) were quantitatively extracted after adjusting aqueous sample solution to pH10.0and7.0, respectively. Mn(?) was calculated by subtraction of Mn(II) from the total manganese. Under the optimized conditions, the LODs (3?) for Mn(?) and Mn(VII) were0.26and1.86ng mL-1, and their RSDs were2.6%and4.8%(C=25.0ng mL-1,n=6), respectively. The method was used for the speciation of Mn(?) and Mn(?) in the certified reference material GBW08513of tea sample and different local tea samples with satisfactory results.(4) A simple, sensitive, and effective method of ultrasound-assisted emulsification of solidified floating organic drop microextraction (USE-SFODME) coupled to electrothermal atomic absorption spectrometry for the speciation of antimony at different oxidation state Sb(?)/Sb(?) in environmental samples was established. In this method, the hydrophobic complex of Sb(?) with sodium di ethyl dithiocarb am ate (DDTC) is extracted by1-undecanol at pH9.0, while Sb(?) remains in aqueous phase. Sb(?) content can be calculated by subtracting Sb(?) from the total antimony after reducing Sb(?) to Sb(?) by L-cysteine. Various factors affecting USE-SFODME including pH, extraction solvent and its volume, concentration of DDTC, sonication time, and extraction temperature were estimated. Under the optimized conditions, the calibration curve was linear in the range of0.05-10.0ng mL"1, with the LOD (3?) of9.9ng L-1for Sb(?). The RSD for Sb(?) was4.5%(C=1.0ng mL-1, n=9). This method was validated against the certified reference materials (GSB07-1376-2001, GBW07441), and applied to the speciation of antimony in environmental samples (soil and water samples) with satisfactory results.(5) A dual-cloud point extraction combined with inductively coupled plasema-optical emission spectrometry (ICP-OES) procedure has been proposed for the speciation of inorganic As(?) and As(?) in water samples. The method based on forming a hydrophobic complex of As(?) with ammonium pyrrolidine dithiocarb am ate (APDC) at suitable pH into a non-ionic surfactant rich phase of Triton X-114. Instead of direct injection or analysis, the surfactant rich phase containing the complex of As(?)-APDC was treated by2.0mol L-1of nitric acid, and the detected As(?) was back extracted again into aqueous phase at the second cloud point extraction stage, and finally determined by ICP-OES. After dual-cloud point extraction, most of matrix interferences like Triton X-114were avoided during the determination of As(?) by ICP-OES. Under the optimum conditions, the LOD (3?) of0.72ng mL-1and the RSD of3.5%(C=10.0ng mL-1, n=5) were obtained for As(?). The feasibility of the proposed method was validated by analyzing inorganic As(?) and As(?) in the certified reference water sample and snow water. The recoveries for the spiked samples were in the range of88.0%-98.0%.