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13 Radiochemical Separation Techniques
3. The selection of the paper is also important and some factors such as the presence
of impurities, the wet strength, the thickness, the flow rate of solvent etc., are
important.
4. Paper chromatograms should not be dried by blowing with air, because this may
cause some of the radioactive nuclides to blow away from the paper. With a βemitter the paper must be thoroughly dried, otherwise the residual solvent will
absorb some of the radiation; this is important when the paper is going to be
counted directly. However, each separated constituent may be extracted from the
paper and can then be counted.
5. Many radioactive nuclides produced by a nuclear reaction have a half-life such
that they must be separated and identified quickly. Paper chromatography can in
such cases be carried out rather rapidly by choosing a fast-moving solvent and
a short paper strip. Usually, a less viscous liquid moves faster and descending
chromatography gives a faster flow rate than ascending.
13.7.2 Paper Electrophoresis
In paper chromatography, the solvent and ions present in the mixture moves due to
gravitational force, but in paper electrophoresis, ions are forced to move by application of potential difference across a paper strip. The paper electrophoresis has been in
use since 1948. Electromigration depends on the different velocities of the substances
under an electric field, so that in principle the stationary solid phases (paper) serves
merely to prevent mixing by convection, while an associated liquid phase serves to
keep the migrant in a mobile form with a suitable charge.
In this technique, unlike that of paper chromatography, a filter paper is moistened
with the chosen so-called background electrolyte solution (such as dilute sulfuric
acid, sodium sulfate etc.). Each end of the strip is dipped into the electrolyte and
a potential difference is applied. Unlike the paper chromatogram, the spot of the
sample is placed in the center of the paper (length-wise) and when the potential is
applied, the ions migrate at different speeds and in different directions depending
upon their nature of the charge. Separation is thus achieved. The separated spots
are spotted on the paper by adopting any of the techniques described earlier. The
separated spots are extracted from the paper by a suitable solvent.
This method is usually more rapid than that of ordinary paper chromatography,
but the calculation of a separation factor, such as R f values, is not so easy because
there may be many factors affecting the separation. Therefore, for identification of
the separated spots, the half-life or energy of radiation emitted by the isotope will
have to be determined.
13 Radiochemical Separation Techniques
3. The selection of the paper is also important and some factors such as the presence
of impurities, the wet strength, the thickness, the flow rate of solvent etc., are
important.
4. Paper chromatograms should not be dried by blowing with air, because this may
cause some of the radioactive nuclides to blow away from the paper. With a βemitter the paper must be thoroughly dried, otherwise the residual solvent will
absorb some of the radiation; this is important when the paper is going to be
counted directly. However, each separated constituent may be extracted from the
paper and can then be counted.
5. Many radioactive nuclides produced by a nuclear reaction have a half-life such
that they must be separated and identified quickly. Paper chromatography can in
such cases be carried out rather rapidly by choosing a fast-moving solvent and
a short paper strip. Usually, a less viscous liquid moves faster and descending
chromatography gives a faster flow rate than ascending.
13.7.2 Paper Electrophoresis
In paper chromatography, the solvent and ions present in the mixture moves due to
gravitational force, but in paper electrophoresis, ions are forced to move by application of potential difference across a paper strip. The paper electrophoresis has been in
use since 1948. Electromigration depends on the different velocities of the substances
under an electric field, so that in principle the stationary solid phases (paper) serves
merely to prevent mixing by convection, while an associated liquid phase serves to
keep the migrant in a mobile form with a suitable charge.
In this technique, unlike that of paper chromatography, a filter paper is moistened
with the chosen so-called background electrolyte solution (such as dilute sulfuric
acid, sodium sulfate etc.). Each end of the strip is dipped into the electrolyte and
a potential difference is applied. Unlike the paper chromatogram, the spot of the
sample is placed in the center of the paper (length-wise) and when the potential is
applied, the ions migrate at different speeds and in different directions depending
upon their nature of the charge. Separation is thus achieved. The separated spots
are spotted on the paper by adopting any of the techniques described earlier. The
separated spots are extracted from the paper by a suitable solvent.
This method is usually more rapid than that of ordinary paper chromatography,
but the calculation of a separation factor, such as R f values, is not so easy because
there may be many factors affecting the separation. Therefore, for identification of
the separated spots, the half-life or energy of radiation emitted by the isotope will
have to be determined.