Authors:C. G. Mothé, A. D. Azevedo, W. S. Drumond, S. H. Wang and R. D. Sinisterra
as wound curative, while the solid copolymers could find application in micro- and nanoencapsulation of drugs [ 8 ]. Tetracycline hydrochloride is a highly water-soluble drug, which acts as an antibiotic and anti-collagenase and has also been reported
The behaviour of tetracycline as an extracting agent for strontium, iodine, barium, molybdenum, technetium, zirconium, niobium, cesium, ruthenium, tellurium and uranium has been studied and the influence of the acidity of the aqueous phase upon extraction of the elements mentioned has been examined. Experiments have been made to determine whether or not the species extracted into the organic phase is the complex formed between tetracycline and the elements considered as well as to determine the time of shaking necessary so that the equilibrium between the phases is attained. As a practical application, the possibility of using the tetracycline-benzyl alcohol system for separating the fission products137Cs,140Ba,140La,141Ce,103Ru,95Zr and95Nb from each other and from uranium is presented. The same study has been made for131I,99mTc,99Mo,132Te,239Np and uranium and the steps necessary for the separation of these elements are proposed.
Stability constants for uranium-tetracycline complexes were determined by the method of average number of ligands, the method of limiting values, the method of two parameters and the method of weighted least squares. Solvent extraction technique was used to obtain experimental data.
Stability constants for thorium complexes with tetracycline were determined by the methods of average number of ligands, the
limiting value, the two parameters and by weighted least squares. The solvent extraction technique was used to obtain the
required data for the determination of the constants.
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.
A chemical procedure has been developed for the separation of U, Th, Fe, Sc, Na, Ta and Mo, which interfere in neutron activation analysis of the lanthanide elements in rocks. This methods in based on the extraction of interferents, before irradiation of the samples, using a solution of tetracycline in benzyl alcohol. The lanthanide elements remain in the aqueous phase and are coprecipitated with calcium oxlate or ferric hydroxide for irradiation and subsequent determination by gamma-ray spectrometry. Conditions for the separation of these interferences are examined determining the extraction curves. The chemical separation procedure was applied in the analysis of lanthanides in geological materials and the results showing the accuracy and the reproducibility of the method are presented. The sensitivity for all the lanthanides was determined.
Tetracycline in solution of benzyl alcohol was used as an extracting agent to separate uranium from interfering elements in the determination of uranium and of isotopic ratio235U/238U by neutron activation analysis. Separation gives a recovery of 97% for uranium and the interferences from matrices of pitchblende and monazite are eliminated.
Hydrogen ion dependence and extractant dependence of the extraction of the lanthanide elements, scandium, uranium and thorium
into a solution of tetracycline in benzyl alcohol have been determined. Possiblity of using the tetracycline-benzyl alcohol
system for separation of the lanthanide elements present in a mixture, as well as for the separation of uranium from those
elements was tested. In the first case discontinuous countercurrent technique was used. In the second case a single step solvent
extraction procedure was applied.