| Plasma chemistry is a rapidly expanding area in science and engineering. In the field of inorganic analytical chemistry, plasma greatly promotes the development of the atomic spectrometry, especially for the microplasma. The reactive free radicals and electrons generated in the plasma could induce a redox process, thus the specific element ions in liquid could be directly turned into volatile gas atoms or molecules through the plasma to realize the element vapor generaion. In addition, since the plasma has a high excitation temperature, it can be used as excitation source for OES or ions source for MS. And the microplasma has unique advantages like small size, low gas consumption and low energy consumption, etc, thus, it is promising to develop miniaturized instruments with low cost using the microplasma as excitation source for OES, or ion source for MS, etc. In the present dissertation, we further investigated the application in the determination of elements by plasma induced vapor generation technology, used for vapor generation of iodine and mercury with different speices simultaneously and designed a new type of portable microplasma excitation source for the miniaturization of instrument, used for the determination of metal elements in water. Based on this, the main research contents of this thesis are as follows:1, A novel method for iodine vapor generation was proposed by SCGD. Both iodide and iodate in the solutioncould be converted to volatile iodine vapor through solution cathode glow discharge induced advanced redox processes. It is achieved by in-situ produced highly reactive chemical species in the discharge, thereby eliminating the need for externally supplied sources of any redox reagents. Iodine vapor is readily generated from a background electrolyte containing 0.01 mol L-1 HNO3. The generated iodine vapor is then transported to inductively coupled plasma for determination by optical emission spectrometry. The influences of the background electrolyte, pH, discharge voltage, carrier gas flow rate and ICP power were examined. The detection limits of plasma induced vapor generation for KI and KIO3 were 0.30 and 0.43μg L-1, respectively. The repeatability, expressed as the relative standard deviation (n=11) of a 0.05 mg L-1 standard, was 1.2% for KI and 1.9% for KIO3. Compared with conventional vapor generation technology, it offers several advantages. First, it eliminates the need for redox regents, and thus minimizes a source of contamination as well as hazards. Second, it is applicable to both iodide and iodate determination. In addition to iodide, iodate could also be directly converted to volatile iodine vapor without prior reduction. The method is sensitive and simple in operation, and requires no auxiliary reagents, served as a useful alternative to conventional vapor generation for trace iodine determination.2. A novel interface was designed based on solution cathode glow discharge (SCGD) induced vapor generation to on-line couple high-performance liquid chromatography (HPLC) with atomic fluorescence spectrometry (AFS) for the speciation of inorganic mercury (Hg2+), methyl-mercury (MeHg) and ethyl-mercury (EtHg). The decomposition of organic mercury species and the reduction of Hg2+ could be completed in one step with this proposed SCGD induced vapor generation system. The vapor generation is extremely rapid and therefore is easy to couple with flow injection (FI) and HPLC. Compared with the conventional HPLC-CV-AFS hyphenated systems, the proposed HPLC-SCGD-AFS system is very simple in operation and eliminates auxiliary redox reagents. Parameters influencing mercury determination were optimized, such as concentration of formic acid, discharge current and argon flow rate. Under the optimum conditions of separation and determination, the three mercury species were fully separatedd within 13 min by using a mobile phase of 0.06 mol L"1 NH4AC and 0.1% 2-mercaptoethanol at pH 6.8. The method detection limits for HPLC-SCGD-AFS system were 0.67 μg L-1 for Hg2+,0.55 μg L-1 for MeHg and 1.19 μg L-1 for EtHg, respectively. The developed method was validated by determination of certified reference material (GBW 10029, tuna fish) and was further applied for the determination of mercury in biological samples.3. A new minituralized tomic emission source setup based on liquid-film dielectric barrier discharge (LFDBD) was developed for microsample elemental determination. It consists of a copper electrode, a tungsten wire electrode, and a piece of glass slide between them, which serves as the dielectric barrier as well as the sample plate. The sample solution with 1 mol L-l nitric acid, when deposited onto the surface of the glass slide, forms a thin liquidfilm. The plasma is generated between the tip of the tungsten wire electrode and the liquid film surface when alternating-current (ac) high voltage (peak voltage-3.7 kV, frequency-30 kHz) is applied on the electrodes. Qualitative and quantitative determinations of metal ions in the sample solution were achieved by atomic emission measurements in the plasma and were demonstrated in this study with elements Na, K, Cu, Zn, and Cd. Detection limits were in the range from 0.6 ng (7 μg L-1) for Na to 6 ng (79 μg L-1) for Zn. Repeatability, expressed as relative standard deviation from seven repetitive analyses of samples with analyte concentrations at 1 mg L-1, varied from 2.1% to 4.4%. Compared with other liquid discharge systems that operate at atmospheric pressure, the current system offers several advantages:First, it eliminates the use of a sample flow system (e.g., syringe or peristaltic pump); instead, a small aliquot of sample is directly pipetted onto the glass slide for analysis. Second, it is a microanalysis system and requires sample volume ≤ 80 μL, a benefit when a limited amount of sample is available. Third, because the sample is applied in aliquot, there is no washout time, and the analysis can be easily extended to sample array for high-throughput analysis. The proposed LFDBD is promising for in-field elemental determination because of its simplicity, cost effectiveness, low power supply, and no inert gas requirement. |
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