Quality Control Procedure for Free Pertechnetate (new elution)
I. Radionuclidic Purity
When Tc-88m is eluted from a Mo-99/Tc-99m generator, Mo-99 could be eluted along with the technetium. This is termed "molybdenum breakthrough." The USP XXIII specifies that technetium radiopharmaceuticals contain no more than 0.15 microcuries of Mo-99 per millicurie of Tc-99m radiopharmaceutical at time of patient administration.
Molybdenum breakthrough and expiration time for the Tc-99m must be determined for every elution from a Mo-99/Tc-99m generator. The expiration time will not exceed 12 hours from the time of elution.
1. Using a calibrated dose calibrator, set the assay for Mo-99 or the most sensitive radioactivity scale.
2. With the empty Mo-99 assay shield in place, zero the calibrator or note the background activity.
3. Working behind a lead shield and using transfer tongs, transfer the Tc-99m pertechnetate eluate vial from the elution shield to the "moly" assay shield.
4. Place the "moly" assay shield containing the eluate into the calibrator well. Note the displayed activity in microcuries.
5. Subtract the background activity and determine the net Mo-99 activity as measured in microcuries.
6. Calculate the total Mo-99 activity by multiplying the net Mo-99 activity by the "moly" assay shield attenutation factor (this factor is supplied by the calibrator manufacturer and can be found in the operation manual for the dose calibrator.
7. Record the total Mo-99 activity and time of assay on the appropriate record.
8. Divide the total Mo-99 activity (in microcuries) by the total Tc-99m activity (in millicuries) to obtain the ratio:
uCi Mo-99/mCi Tc-99m.
9. Determine eluate shelf life with the equation t = [(-ln Mc/Tc)/0.1052] -18.03
II. Chemical Purity
When a Mo-99/Tc-99m generator is eluted, it is possible to elute aluminum ion along with the Tc-99m. The USP XXIII allows no more than 10 micrograms of aluminum ion per milliliter of Tc-99m eluate from a fission-produced generator. Excessive aluminum indicates lack of stability of the generator column.
Commercially available colorimetric test kit for aluminum ion
1. Place one drop of standard solution on an indicator strip provided in the kit. The standard solution contains 10 micrograms per milliliter of aluminum ion.
2. Working behind a shielded work station, aseptically withdraw a small amount of eluate. Place a drop of the eluate on the indicator strip next to the standard solution spot.
3. Compare the color intensity of the two spots.
4. If the eluate spot is more intense (darker) than the standard, the aluminum is in excess. The eluate must be discarded.
5. Follow any additional kit directions and record results as positive or negative.
III. Radiochemical Purity
In radiopharmaceutical kits, Tc-99m becomes attached to a substrate molecule, the ligand, designed to localize in a specific organ system. Both free Tc-99m and hydrolyzed reduced Tc-99m, resulting from the tagging process, can give artifacts on the scanning. That may lead to mislead clinical diagnosis or difficulty in assessing scans. Radiopharmaceuticals must be efficiently tagged to ensure accuracy of patient diagnosis.
The USP XXIII has set minimum tagging efficiency standards for most radiopharmaceuticals. Each pharmaceutical compounded must be tested for radiochemical purity before use in a patient. In testing Tc-99m eluate for radiochemical purity, only the free sodium pertechnetate is desirable. Purpose of this procedure is detection of hydrolyzed reduced Tc-99m in the eluate.
Whatman 3 MM
MCA or SCA or Scaler with scintillation well
1. See General QC Procedures. Spot sodium pertechnetate eluate on the Whatman 3 MM strip.
2. Develop the strip in Acetone. Count each half of the strip in a scintillation well.
3. Free sodium pertechnetate is located at solvent front (top); Hydrolyzed reduced is located at the origin (bottom).
4. Calculate: % free Tc-99m = top counts/(bottom counts + top counts) x 100
5. USP XXIII minimum acceptable purity: 95%