Study Of Chemiluminescence And Mercury Cold Vapor Generation Based On Photo-Assited Reactions

The principle, analytical application and recent development of photochemical reactions, including photolysis and photocatalysis were reviewed. Furthermore, the principle and the latest development of chemiluminescence (CL) and atomic absorption spectrometry (AAS) were also introduced in detail. Photochemical-assisted chemiluminescence is a new analytical technique, in which analyte is decomposed into new active substances that react with other reagents to produce CL. Thus, it helps to broaden the area of CL application. Additionally, based on photochemical reactions, a new chemical vapor generation technique for atomic spectrometry has been developed rapidly and has raised wide attention. Therefore, the aim of this work is to extend the analytical potential of photochemical reactions coupled to CL and AAS and to develop new HPLC-CL technologies, including the on-line determination of chemical oxygen demand (COD), speciation analysis for selenoamino acids and the determination of mercury. Furthermore, using these established methods, analytical applications in environment, foods and life sciences were investigated. Lastly, as an additional application of AAS in pharmaceutical analysis, indirect atomic absorption spectrometry (IAAS) was also investigated and an IAAS method was established for the determination of riboflavin in Vitamin B2 tablets and injections.1. A novel on-line method based on the combination of UV photolysis and chemiluminescence detection was established and experimentally validated for the determination of chemical oxygen demand (COD). A quantitative amount of free radicals can be generataed from analytes in the UV irradiation process. By utilizing the phenomenon that luminol can be oxidized by the free radicals to produce luminescence, COD was successfully determined indirectly. This new approach overcomes many problems associated with the conventional COD determination techniques such as long analysis time, tedious operations, consumption of expressive and toxic reagents, production of secondary toxic waste and poor reproducibility. The method was successfully applied to the determination of COD in synthetic samples, certified reference samples and real samples of river water and lake water. A limit of detection of 0.08 mg L^-1 COD with a linear dynamic range of 0.2²0 mg L^-1 was achieved under the optimum experimental conditions. The proposed method is a unique method that is environmentally friendly (without using any strong oxidizing reagent and any catalyst such as titanium dioxide), rapid (with only 5¹0 min required for each sample), sensitive (with the lowest limit of detection for COD so far), simple (mainly using a photo-reactor and a chemiluminescence detector) and automated (using an intermittent flow system).2. Based on the combination of liquid chromatography (LC), UV/Nano-TiO₂ photocatalysis and chemiluminescence detector, a novel hyphenated technique for the speciation of selenocystine (SeCys) and selenomethionine (SeMet) was established. Analytes were separated on an anion exchange column (Hamilton PRP X^-100) and then mixed with Co(II) solution for decomposition in a specially designed UV/TiO₂ photocatalysis reaction device (PCRD). The decomposition products can inhibit the CL of luminol and the inhibited CL intensity is linear with the concentration of the analyte. For 100μL sample, the limits detection of 3 and 5μg L^-1 were achieved for SeCys and SeMet, respectively. Compared with other hyphenated techniques, such as HPLC-HG-ICPMS, HPLC-HG-AFS and HPLC-HG-AAS, this technique is simpler and more cost-effective due to the cheaper detector, immobile TiO₂, fewer reagents, interfaces and components (without a gas liquid separator and a carrier). The method was applied to determine Selenoamino acids in garlic, in which SeMet was the only detected species, and a rabbit serum, in which smaller fractions of SeCys and SeMet were found besides a major unknown species. Selenoamino acid standard was spiked into the four samples and good spiked recoveries from 88 to 104 % were obtained.3. A new method based on slurry sampling atomic absorption spectrometry (AAS) was established for the determination of trace mercury in geological samples by use of recently developed mercury cold vapor generation using formic acid under ultraviolet (UV) irradiation. The mercury cold vapor generated was rapidly separated from the matrix and swept into a T-tube for the measurement of atomic absorbance. Under the optimal experimental conditions, up to 1000-fold of Cu(II), Co(II), Ni(II), Cr(VI), Mn(II), Fe(III) and Zn(II) caused no significant interferences with the determination of 50μg L^-1 Hg. The limit of detection at sub-ppb level was obtained. The method was successfully applied to the determination of mercury in geological samples with satisfactory results.4. A flame atomic absorption spectrometric method was developed for the indirect determination of riboflavin. An excess sodium periodate was used to react with riboflavin, the remaining periodate was precipitated with excess lead nitrate or copper nitrate. The formed precipitation, lead periodate or copper periodate was separated from the reaction medium by membrane filtration, and then was dissolved in 0.2 mol L^-1 nitric acid following the analysis of lead or copper by flame atomic absorption spectrometry. The calibration curve was linear over the range of 1 20μg mL^-1 and 2.5 50μg mL^-1with lead nitrate or copper nitrate, respectively. The relative standard deviation (RSD) for the determination of 5μg mL^-1 riboflavin was 4.8 % and 5.2 %, and the detection limit was 0.6 and 0.5μg mL^-1, respectively, for the case of lead nitrate or copper nitrate. The method was used for the determination of riboflavin in Vitamin B2 tablets and injections.