Application Of In-situ Generation Of Hydrous TiO₂-Dispersive Micro Solid Phase Extraction For Analysis Of Environmental And Biological Samples

Dispersive solid phase extraction（d-SPE）, which was first reported in 2003, is considered as a quick, easy, cheap, effective, rugged and safe sample preparation method. In this experiment, we proposed a new method named hydrous TiO₂-based in-situ dispersive micro solid phase extraction（in-situ d-μ-SPE）. This method was based on the injection of the mixture of tetrabutyl titanate（TBOT） and ethanol（dispersive solvent） into the aqueous sample to hydrolyze hydrous TiO₂ to adsorb analytes in-situ. The large contact surface between the dispersive adsorbent and the sample speeds up the adsorption process and improves the extraction efficiency. This simple and fast method had wide applications in trace analytical chemistry.The major contents were summarized as follows.（1） We have studied the affect factors in the generation process of precipitation, characterized the adsorbent, such as SEM, TEM and FT-IR, measured the zero charge point of adsorbent. It was found that TBOT could hydrolyze in pH value of 6-8. The SEM and TEM showed the diameters of these fine particles are between 20-80 nm and they distribute uniformly in the sample solution. Many tiny particles reunited into the size of 2-10 μm precipitation. The FT-IR showed a wide and strong peak at 3600-3000 cm-1 and 1600 cm-1, that are-OH stretching vibration and bending vibration. According to the measurement of zeta potential, we knew the zero charge point of hydrous TiO₂ was 5.75. High disperation of hydrous TiO₂ nanoparticals obtained by simply injection of a portion of TBOT-ethanol into the aqueous sample, which achieve a huge surface of the adsorbent and a quick extraction equilibrium.（2） A novel method of in-situ d-μ-SPE combined with graphite furnace atomic absorption spectrometry（GFAAS） was developed for the determination of Pb²⁺ and Cd²⁺ from environment water sample. Pb²⁺ and Cd²⁺ were adsorbed without pH adjusting. All the factors involved in the extraction process have been studied. Under the optimized performance, the detection limites（S/N=3） of Pb²⁺ and Cd²⁺ were 0.010 and 0.0054 μg/L with the RSD lower than 4.4%. The south lake water and tap water were successfully analyzed for the existence of Pb²⁺ and Cd²⁺ using the proposed method and the relative recoveries were 90.4-99.1%.（3） The method of in-situ d-μ-SPE combined with high performance liquid chromatography（HPLC） was developed for the extraction and determination of four endocrine disrupting compounds（EDCs） in environment water sample. All the factors involved in the extraction process have been studied. Under the optimized performance, a wide linearity with correlation coefficients（R2） ≥ 0.912 was obtained. The detection limites（S/N=3） of EDCs were 0.18-2.16 μg/L. The south lake water and youth lake water were successfully analyzed for the existence of EDCs using the proposed method and the relative recoveries were 95.0-112.5% with the RSD lower than 7.1%.（4） The novel method of in-situ d-μ-SPE combined with high performance liquid chromatography（HPLC） was developed for the determination of nucleosides in plasma sample. TiO₂（Lewis acid） could bind with cis-diol structures（A, C, G and U; Lewis base） and carried many hydroxyl groups to adsorb deoxynucleosides（2′-dA, 2′-dC, 2′-dG and T） through the mechanism of hydrophilic interaction. The experiments showed 2′-dA, 2′-dC, 2′-dG and T could be captured in acetonitrile solution with the water content less than 10%, whereas the adsorption of A, C, G and U would not be affected by water or acetonitrile. When all nucleosides were adsorbed, water and 2% formic acid solution were used to release deoxynucleosides and ribonucleosides, respectively. Finally, A, U, 2′-dC and 2′-dG were used to optimize extraction factors and evaluate method in acetonitrile solution with 10% water. The LOD of nucleosides were 0.43-3.06 ug/L. The relative recoveries of spiked plasma samples were 93.3-101.7%, with RSD less than 8.8%.