Yttrium-90 and Rhenium-188 Radiopharmaceuticals for Radionuclide Therapy

A–2.2. Materials
The method for separation of 90 Sr from 90 Y eluate is based on the
commercially available strontium resin obtained from Eichrom Technologies.
This is an extraction chromatography resin coated with a 1.0M solution of the
crown ether 4,4’(5’)-di-butylcycloexane 18-crown-6 1.0 in 1-octanol as the
extracting system. This extractant has different stability constants (pH dependent)
for different cations, which is a property resulting from both steric interactions
with the cavity of the 18-crown-6 ether and electrostatic forces between the
oxygens of the ether and the cations dissolved in the mobile phase. In particular,
this strontium resin has a high stability constant for Sr 2+ at low pH (high acidic
concentration), whereas in the same conditions, the stability constant for Y 3+ is
very low.
In the initial experiments, the solution containing 90 Sr and 90 Y was loaded
onto a strontium resin minicolumn (2 mL cartridge), the 90 Y was eluted with two
fractions of 5 mL of 8.0M HNO 3 to collect the 90 Y, and then the two fractions
were eluted with 5 mL of 0.01M HNO 3 , each to recover the 90 Sr from the column.
According to Eichrom Technologies specifications, this procedure should allow
collection of pure solutions of each radionuclide. Unfortunately, this was not
confirmed in the liquid scintillation counting and spectrometric analysis. This led
to improvements of the conditions for separation, as published earlier [A–8] and
presented in the method below.
A–2.3. Method
The technique was performed as described in the following steps:
(a)
(b)
Column preparation: 4 mL of the Eichrom Technologies strontium resin
prepared according to manufacturer recommendations was loaded onto a
chromatographic column (dimensions of 1 cm × 5 cm).
Elution procedure: The 90 Y– 90 Sr eluate mixture was loaded onto the freshly
prepared strontium resin column. Two 5 mL fractions of HNO 3 (8.0M) were
successively passed through the column. Activity corresponding to 90 Y was
recovered almost quantitatively in the first 5 mL fraction. The elution with
HNO 3 (8.0M) was continued by collecting and counting smaller portions of
the second fraction until the 90 Y radioactivity was below the detection limit,
thus indicating that 90 Y will not interfere with the subsequent counting of
90 Sr. Finally, 90 Sr was stripped from the column by successively passing
two 5 mL fractions of HNO 3 (0.01M). These solutions were collected and
counted and the ratio 90 Sr: 90 Y calculated.
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