Method development for the quantification of the rare earth elements europium, dysprosium, terbium and yttrium

English: The metal nitrate salts (Ln(NO3)3∙xH2O) of the four REEs were successfully dissolved (visual inspection) in HNO3 and recoveries of 100.0(2) % for europium, 100.(7) % for terbium, 99.4(1) % for yttrium and 75.6(4) % for dysprosium were obtained. The unsatisfactory recovery results (in spite of the absence of any remaining material after dissolution) of dysprosium prompted a further investigation to determine the appropriate molecular formula of the Dy(NO3)3·xH2O salt. Thermogravimetric analysis (TGA) was used to determine the number of crystal waters and results indicated the most appropriate molecular formula should be Dy(NO3)3·6H2O. This improved the dysprosium recoveries to 99.6(1) %. The same five acids (HNO3, HCI, H2SO4, H3PO4 and aqua regia) were used in an attempt to dissolve the newly synthesized organometallic TPPO complexes. The formation of two immiscible liquids after digestion rendered these methods unsuccessful. Microwave digestion with 98 % H2SO4 managed to completely dissolve all of these organometallic complexes without the formation of the two colourless (oil and water) layers. The recoveries of 99.10(6) %, 99.4(4) %, 99.9(3) % and 96.1(5) % for europium, terbium, dysprosium and yttrium respectively were obtained. Infrared (IR) and CHNS micro analysis were used to characterize the different TPPO complexes. The IR spectra of the different complexes compared favourably with the previously prepared and reported compounds while excellent % C and H values were obtained. Interestingly and against expectations, poor % N values were obtained for all the complexes. The experimental results for the quantitative analysis of europium, terbium, dysprosium and yttrium obtained from the metals, inorganic compounds and synthesized organometallic TPPO complexes were validated using ICP-OES results. The statistical validation of all the analytical results was performed at a 95 % confidence interval. Validation of the obtained results also included the evaluation of parameters such as linearity, sensitivity, accuracy, precision, specificity, LOD, LOQ and robustness. Unsuccessful dissolution, low recoveries and small standard deviations are the reasons why some of the results (even at +99 % recovery) were rejected.