The Study Of Fluorometric Determinations Of Rare Earth Elements

The fluorometric determinations of rare earth elements cerium, lanthanum, samarium and gadolinium were studied in the paper. And the main points were as follows:1. The theory, characteristic, systematics and applications of the fluorescence analysis were introduced and lay the emphasis on the summary of the catalytic kinetic fluorescence method on thoese aspects above. Secondly, the application and development of fluorescence analysis in the REs were reviewed comprehensively. Furthermore, it looks to the brighter future of the applications of the fluorescence analysis for the determinations of REs.2. Cerium(Ⅲ) ion was a rare earth element possessed the property of fluorescence and with its excitation and emission wavelengths of 303 nm and 349 nm respectively. So cerium(Ⅳ) should be reduced to cerium(Ⅲ) which could be analyzed by fluorescence method. In the experiment, stannous was chosen as the reductant with its concentration of 0.001 mol/L. In order to improve sensitivity of the method,0.01 g/L sodium tripolyphosphate was added in the system. The optimum reaction temperature was 70℃in the water bath, and the optimum reaction time was 20 min. The linear range of the proposed method was 0.4～1.2μg/mL, and the detection limit was 0.0374μg/mL. The proposed method was successfully applied to the determination of trace cerium in the copper alloy samples with its relative standard deviation (RSD) of 0.18% to 0.30% and the recovery of 97.9%～104.2%.3. A new system of La(Ⅲ)-8-hydroxyquinoline-Eosin Y for the determination of trace lanthanum was established in the paper. The optimum experiment conditions were discussed:acetic acid-sodium acetate solution as the reaction medium,2.5 mL Eosin Y with its concentration of 1×10-4 mol/L,2.0 mL 8-hydroxyquinoline standard solution. The optimum reaction temperature and time were 50℃and 15 min respectively. In addtion, both the apparent rate constant and apparent activation energy were determined and they were 0.01/s and 71.6 kJ/mol respectively. The linear range of the method in the experiment was 0.2～1.2μg/mL, and the detection limit was 5.4×10-4-4μg/mL from which it showed a high sensitivity. And the proposed method could be applied to the determination of trace lanthanum in lanthanum amalgam. The recovery was between 99% and 106 %, the relative standard deviation (RSD, n=6) was 1.1%～2.1%. 4. A new system for the determination of samarium by kinetic fluorometric method was established based on the inhibitory effect of samarium on the redox reaction between potassium persulfate and Rhodamine B in sulfuric acid solution. The apparent activation energy and apparent reaction rate constant were determined in the paper and were 21.50 KJ/mol and 0.03/s respectively. The linear range of the proposed method was 0.040～0.18μg/mL, and the detection limit was 2.67×10-4μg/mL. It can be used for the application of the determination of trace samarium in silver alloy samples of which the recovery was 96% to 106% and the relative standard deviation (RSD) was between 1.1% and 3.1%, the results were accurate and reliable.5. A new system for the determination of gadolinium was established based on the significant catalytic effect of gadolinium on the reaction of potassium persulfate with Saffron T in acidic solution. The optimum conditions were investigated in the paper:Saffron T with 8.0×10-6 mol/L, potassium persulfate with 6.0×10-4 mol/L, the acidity was pH 4.0 to 6.0, thus acetic acid-sodium acetate solution was choosen as the reaction medium. The optimum reaction time was 10 min and the temperature was 65℃. The linear range was 0.02～0.10μg/mL and the detection limit was 0.075μg/mL. The proposed method was applied to the determination of gadolinium in the gadolinium oxides of which the the relative standard deviation (RSD) was 0.9%～3.1%. Finally the mechanism of the catalytic dynamic reaction was explored.