The use of the antibiotic agent tetracycline for analytical purposes in solvent extraction procedures is presented. Individual
extraction curves for the lanthanides, zinc, scandium, uranium, thorium, neptunium and protactinium were obtained. Separation
of those elements one from another, and of uranium from selenium, bromine, antimony, barium, tantalum and tungsten was carried
out. In all cases benzyl alcohol was the diluent used to dissolve tetracycline hydrochloride. Sodium chloride was used as
supporting electrolyte for the lanthanide separations and sodium perchlorate for the other elements mentioned. Stability or
formation constants for the lanthanide complexes as well as for thorium complex with tetracycline were determined by using
the methods of average number of ligands, the limiting value (for thorium), the two parameters and the weighted least squares.
For the lanthanides, the stability constants of the complexes Ln(TC)3 go from 9.35±0.22 for lanthanum up to 10.84±0.11 for lutetium. For the Th(TC)4 complex the formation constant is equal to 24.6±0.3. Radioisotopes of the respective elements were used for the determinations.
When more than one radioelement was present in an experiment, a multichannel analyser coupled to Ge(Li) or NaI(Tl) detectors
was used for counting the activities. When only one radioisotope was used, counting of the radioisotopes was made with a single-channel
analyser (integral mode counting) coupled to a NaI(Tl) detector. Uranium was determined by activation analysis (epithermal
neutrons). Radioisotopes of the elements were obtained by irradiation in the IPEN swimming-pool reactor. The natural radioisotope2 3 4Th was used as label in the thorium experiments. In some separation procedures such as in the case of the pair uranium-neptunium,
and of the pair scandium-zinc, the separation was obtained by properly adjusting the pH value of the aqueous phases, before
the extraction operation. In other cases, addition of masking agents to the extraction system was required in order to perform
the separation between the elements under study. In this way ethylenediaminetetraacetic acid (EDTA) was used as masking agent
for scandium and the lanthanides in order to allow separation of uranium from those elements. Diethylenetriaminepentaacetic
acid (DTPA) was used as masking agent for thorium in order to extract uranium into the organic phase. Separations of protactinium
from thorium, and of uranium from protactinium and thorium, were accomplished by using sodium fluoride as masking agent for
protactinium and DPTA as masking agent for thorium and protactinium at the same time. In the case of the separation of the
lanthanides one from another it is necessary to resort to a multi-stage extraction procedure since the stability constants
for those elements are too close.