Analytical chemistry of lanthanides
The work described in this thesis consists of nine chapters. The first chapter is a general introduction, where lanthanide elements and their application are presented. Candoluminescence is defined as a type of solid state luminescence excited by hydrogen-based flame, and its relation to similar phenomena are clarified. A detailed historical review of candoluminescence of the lanthanides and its theoretical aspects are reported. Also a general introduction on vidicon detectors is given. In chapter two instrumental developments for monitoring candoluminescence spectra and intensities and methods of improving the reproducibility of candoluminescence measurements are reported. Automated matrix introducing and matrix making devices are described, and methods for wavelength calibration of the Optical Spectrum Analyzer are reported. Chapters three and four describe the candoluminescence of terbium and europium respectively. Terbium gives a characteristic green emission in MgO and rare earth oxides (Y₂O₃, La₂0₃, Gd₂O₃ and Lu₂O₃ ) coated on CaO matrices. It was possible to determine 0.1 - 50 ng of terbium in Gd₂O₃ coated matrices with a 0.01 ng detection limit and 2.5% relative standard deviation (r.s.d.). Europium was a new activator for the above rare earth oxides coated on CaO matrices in which it gives a red emission. It was possible to determine 0.1 - 15 ng of europium in such a matrix with a detection limit of 0.05 ng and 2.6% r.s.d. In chapter five a general introduction for fluorescence analysis and flow injection analysis (FIA), their principles, instrumentation and applications for lanthanides determination are given. Chapter six describes a flow injection spectrofluorimetric method for determination of cerium(lll) (1-100 ng ml¯¹ ) based on its native fluorescence in an acidic carrier stream. Cerium(lV) can similarly be determined by incorporating a zinc reductor minicolumn into the system. Splitting the injection sample so that only part passes through the reductor, and the remainder by-passes it, allows total cerium and cerium(lll) to be detected from the two sequential fluorescence peaks obtained. Chapter seven describes a very selective flow injection method for determination of 0.5 - 4 µg m¯¹ europium. A zinc reductor minicolumn is used for reduction of europium(lll) to europium(ll), which is indirectly detected either spectrofluorimetrically by reaction with cerium(lV), and measurement of the cerium(lll) produced, or spectrophotometrically by reaction with iron(lll), and determination, with 1,10-phenanthroline, of the iron(ll) formed. Chapter eight describes a sensitive and selective flow injection spectrofluorimetric method for samarium, terbium and europium determinations. The method utilizes the formation of energy-transfer complexes between the lanthanide ions and hexafluoracetylacetone. Finally in chapter nine, some general conclusions are drawn, and possible areas of future research are suggested.