| A complete sample analysis procedure includes four steps as follows, (1) sample collection and storage; (2) sample pretreatment; (3) instrumental analysis; (4) data analysis. Among them, sample pretreatment is a crucial step, which has become the bottleneck for the development of analytical method and a hot research topic in morden analytical chemistry. Sample pretreatment aims to eliminate the matrix effect and enrich the analytes, and thus to improve the analytical performance. Nowadays, sample pretreatment has been tending to be miniaturized, simple and environmental friendly. In recent years, there have appeared various miniaturized sample pretreatment techniques, such as liquid phase microextration (LPME), solid phase microextraction (SPME) and stir bar sorptive extraction (SBSE) etc. Of all these newly developed miniaturized sample pretreatment techniques, LPME, which was developed from liquid liquid extraction in 1996, has arisen great interest in analytical community due to its advantages of easy to operate, low-cost and low solvent/sample consumption, and has been applied to trace/ultra trace analysis in many fields, such as environment, food, and biology. However, there are still some problems that call for solution or improvement, such as the stability of single drop in single drop microextraction, the development of on-line or automated LPME system and more applications in elemental speciation, and so on.The aim of this dissertation is to develop new LPME device or system; to study the factors which influence the microextraction efficiency in detail; to design and construct an on-line LPME device; and to develop new methods by combining LPME with HPLC for the analysis of organic compounds and elemental speciation. The major contents of this dissertation are described as follows:(1) A new method by combining headspace single drop microextraction (HS-SDME) with HPLC fluorescence detection for the determination of trace polycyclic aromatic hydrocarbons (PAHs) in environmental samples was developed. Aqueous solution of saturatedβ-cyclodextrin was used as extraction solvent and five PAHs were employed as target analytes. The factors, such as extraction temperature, extraction time, stirring rate and salt effect, affecting the extraction efficiency were studied in detail and the optimal extraction conditions were established.β-cyclodextrin was found to play two important roles, one is to improve the extraction efficiency of target analytes and the other to enhance their fluorescence intensities in HPLC fluorescence detection. The detection limits for the target analytes were found to be in the range of 0.004-0.247 ng/mL and the relative standard deviations (RSDs) of 5.6-7.1% were obtained. The proposed method was applied to the analysis of trace PAHs in environmental samples with satisfactory results.(2) A "U" shape headspace hollow fiber liquid phase microextraction (HS-HF-LPME) device was designed to increase the volume of extraction solvent in the headspace. And, two sample pretreatment methods based on HS-SDME and HS-HF-LPME were developed and critically compared for the analysis of phenols (including phenol (Ph),2-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP)) in water, honey and toner samples with HPLC-UV detection. The significant parameters affecting the extraction efficiency of the target analytes in both extraction modes were studied and the optimal extraction conditions were established. Under the respective optimal conditions, the analytical performance of HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were compared. Since there was no direct contact between the extraction solvent and sample matrix, both HS-SDME-HPLC-UV and HS-HF-LPME-HPLC-UV were performed without interference. The operation of HS-SDME is simpler than HS-HF-LPME, while HS-HF-LPME is more robust than HS-SDME and can tolerate a relatively high stirring rate. In addition, compared to HS-SDME, extraction solvent supported by hollow fiber in HS-HF-LPME has larger specific surface area, which helps the analytes with less volatility reach the extraction equilibrium in a shorter time. The sensitivity of four target analytes was improved obviously by using variable-wavelengths UV detection. Either HS-SDME or HS-HF-LPME combined with HPLC-UV has been demonstrated to be an effective method for the analysis of phenols in real world samples with different matrix.(3) Hollow fiber based liquid-liquid-liquid microextraction (HF-LLLME) combined with HPLC-UV detection was developed for the simultaneous determination of four acidic phytohormones (salicylic acid (SA), indole-3-acetic acid (IAA), (±) abscisic acid (ABA) and (±) jasmonic acid (JA)) in natural coconut juice sample for the first time. By the use of phenetole filled the pores of hollow fiber as the organic phase and 0.1 mol/L NaOH solution in the lumen of hollow fiber as the acceptor phase, a simultaneous preconcentration of four target analytes in 1 mol/L HCl medium as the donor phase was realized. The acceptor phase was finally withdrawn into the microsyringe and directly injected into HPLC for the separation and quantification of target phytohormones. The factors affecting the extraction efficiency of HF-LLLME were optimized by orthogonal design experiment, and the data was analyzed by Statistical Product and Service Solutions (SPSS) software. Under the optimized conditions, the enrichment factors for SA, IAA, ABA and JA were 243,215,52 and 48, with the detection limits (S/N=3) of 4.6,1.3,0.9 ng/mL and 8.8μg/mL, respectively. The RSDs (n=7) obtained by this method were 7.9,4.9,6.8 and 8.4% for SA, IAA, ABA at 50 ng/mL level and JA at 500μg/mL, respectively. For validation, the developed method was applied for the simultaneous analysis of multiple phytohormones in natural coconut juice, and the recoveries for the spiked sample were in the range of 88.3-119.1%. The proposed method is simple, selective, sensitive and inexpensive for the simultaneous quantification of multiple phytohormones.(4) A hollow fiber based liquid-liquid-liquid microextraction (HF-LLLME) system was developed for simultaneous preconcentration of inorganic mercury (Hg(II)), methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) prior to HPLC-ICP-MS detection, and a new method was proposed for the speciation analysis of mercury in a micro-ecosystem of East Lake. With 1-(2-pyridylazo)-2-naphthol (PAN) as the chelating reagent, four mercury species was first extracted into the organic phase (toluene) in the form of hydrophobic complexes; and then, they were transferred to Na2S2O3 aqueous solution in the hollow fiber lumen as acceptor phase. The factors effecting the extraction were investigated by orthogonal design experiment, and the data was analyzed by SPSS software. Under the optimized conditions, the detection limits for four mercury species were in the range of 2.9-5.6 ng/L (as Hg) with precisions (RSDs (%), c=0.5μg/L (as Hg), n=7) ranging from 5.6 to 10.6%. The developed method was validated by analyzing a certified reference material (DORM-2, dogfish-muscle, NRCC), and the determined values were in good agreement with the certified values. Finally, the proposed method was applied for the speciation of mercury in five representative samples collected from the micro-ecosystem of East Lake with satisfactory results. (5) A method based on solidified floating organic drop microextraction (SFODME) in combination with HPLC-ICP-MS was proposed for the speciation analysis of organotin compounds (monobutyltin trichloride (MBT), dibutyltin dichloride (DBT), tributyltin chloride (TBT) and triphenyltin chloride (TPhT)) in environmental samples. Sodium diethyldithiocarbamate (DDTC) added into sample solution was used as the chelating reagent, and a mixture of p-xylene and 1-dodecanol was used as the extraction solvent. After extraction for 20 min, the sample solution was frozen in the refrigerator for 5-10 min, and the solidified extraction solvent was separated from the sample solution and transferred into a micro container. After melting in room temperature, the extract was diluted with acetone, and injected into HPLC-ICP-MS for subsequent analysis. Several parameters affecting extraction efficiency (such as pH of sample solution, concentration of DDTC, stirring rate, extraction time and salt effect) were optimized. Under the optimal conditions, the detection limits for the target analytes were in the range of 5-20 ng/L (as Sn) with RSDs (%), (cMBT, DBT=0.5 ng/mL, CTPhT.TBT=2ng/mL, n=7) ranging from 8.4 to 14.8%. The proposed method was validated by standard reference material PACS-2, and then successfully applied for the organotin speciation in water and sediment samples with recoveries in the range of 79.0-116.2% for the spiked samples.(6) A new method by combining HF-LLLME with HPLC-ICP-MS was proposed for speciation analysis of selenoamino acids (L-Selenocystine (SeCys2), DL-Selenomethionine (MetSe), Se-methylseleno-L-Cysteine (MeSeCys), Seleno-D, L-Ethionine (EtSe)), and the distribution of target selenoamino acids in clover sample was investigated. The extraction mechanism of selenoamino acids, which are zwitterionic compounds, in HF-LLLME with di-2-ethylhexyl phosphoric acid (P204) as organic phase was investigated. The parameters affecting extraction were examined and optimized. Under the optimal conditions, the detection limits obtained for SeCys2, MeSeCys, MetSe and EtSe were 1.47,0.45,0.078 and 0.089 ng/mL (as Se), respectively, with RSDs in the range of 5.5-8.3%(cSeCys2, MeSeCys=50 ng/mL, CMetse, Etse=5 ng/mL, n=7). The developed method was validated by analyzing a certified reference material (SELM-1), and the determined values were in good agreement with certified values. The analytical results obtained for selenoamino acids in clover samples indicated that no target selenoamino acids was detected in the clover samples without selenium irrigation, while MetSe was quantified in clover samples after periodical selenium irrigation demonstrating an effective accumulation ability of clover for selenium. And the content of MetSe in clover root is higher than that in stem or leaf in clover samples after periodical selenium irrigation.(7) A self-designed LPME device was proposed for on-line combination with HPLC-UV analysis of amphetamine (AP) and methamphetamine (MAP) in urine samples. The developed on-line LPME-HPLC-UV method integrates extraction, enrichment, purification, separation and determination into one step. The parameters affecting extraction of the target analytes were examined and optimized. Under the optimized conditions, a linear range of 5-1000 ng/mL was achieved for both compounds, with detection limits of 1.36 and 0.81 ng/mL for AP and MAP, respectively. And the RSDs (c=20 ng/mL, n=11) for two target analytes were less than 10%. The proposed method has been successfully applied to the quantification of AP and MAP in urine samples collected from both healthy persons and drug abusers. |
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