Determination of zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten in aqueous solutions by radioisotopic excited x-ray fluorescence

Previous investigations on the quantitative determination of sulfur, chlorine, potassium, calcium, scandium and titanium in aqueous solutions by a radioisotopic excited fluorescent spectrometer has been extended to include other elements which are very difficult to separate and determine quantitatively by chemical methods. Six elements taken for the investigation and some of the results to be presented in this paper are: (1) zirconium, (2) hafnium, (3) niobium, (4) tantalum, (5) molybdenum and (6) tungsten. As in previous investigations, aqueous solutions have been used because of the ease in obtaining exact concentrations and homogeneous mixtures of the elements under investigation. In the earlier investigations which have been reported in this conference, lighter elements (atomic numbers ranging from 16 to 22) were used for the investigation. In the present studies, however, comparatively heavier elements have been used. Therefore a radioisotope such as iron 55 used earlier is not suitable because it cannot excite the K x-ray of these elements. To excite the K and L of these elements, we use the radioisotope iodine 125. The advantage of using this radioisotope is that it is inexpensive and commercially available although its half-life is comparatively short. The spectrometer used with further improvements has been described and presented earlier. We used a multi-channel analyzer of 1000 in the present investigation, A liquid cell was specially designed for thisr study. Chemicals used for preparation of solutions were of reagent grades. Some of them had to be specially prepared. For example, hafnium, often contaminated with zirconium, was specially prepared and checked spectroscopically. Some difficulties have been encountered in preparing concentrated solutions such as niobium and tantalum due to the inherit characteristics of these elements to form insoluble compounds. Procedures will be described for the preparation of these solutions. Instruments used and results will be presented in this paper.