Sodium Iodide (131I) Capsules for Diagnostic Use
Category. Diagnostic.
Sodium Iodide (131I) Capsules for Diagnostic Use containing iodine-131 in the form of sodium iodide on a solid
support. They may contain sodium thiosulphate or some other suitable reducing agents and a suitable buffering
substance. A package contains 1 or more capsules.
Sodium Iodide (131I) Capsules for Diagnostic Use contains Iodine-131not more than 37 MBq per capsule.
The average radioactivity determined in the test for uniformity of content is 90.0 per cent to 110.0 per cent of
the stated iodine-131 radioactivity at the date and time stated on the label.
Identification
A. Determine by gamma-ray spectrometry. The most prominent gamma photon has an energy of 0.364 MeV.
B. In the test for Radiochemical purity, the principal peak in the radiochromatogram obtained with test
solution (b) is similar in retention time to the principal peak in the radiochromatogram obtained with
reference solution (a).
Tests
Radioactivity assay. Radioactivity of an aliquot of Test Solution is assayed using precalibrated radioactivity
dose calibrator as described in measurement of radioactivity. It is expressed as MBq(mCi) in volume V ml at a
particular time and date.
Disintegration. Not more than15 minutes.
In a water-bath at 37 °, warm in a small beaker about 20 ml of a 0.2 per cent w/v solution of potassium iodide.
Add a capsule under examination. Stir magnetically at 20 revolutions per minute.
Uniformity of content. Determine the radioactivity of not less than 10 capsules. Calculate the average
radioactivity per capsule. The radioactivity of no capsule differs by more than 10 per cent from the average, the
relative standard deviation is not more than 3.5 per cent.
Radionuclidic purity. Determine by gamma-ray spectrometry.
Iodine-131 is not less than 99.9 per cent of the total radioactivity.
Dissolve the capsule in approximately 5 ml of warm water and take a drop of this solution in glass vial and place
the vial on the detector for gamma spectrometry. OR the spectra can be taken directly using the capsule.
Examine the gamma ray spectrum of the preparation. The most prominent gamma photon has an energy of
0.365 MeV.
Radiochemical purity. Determine by liquid chromatography (2.4.14) as described under Iodide using
radioactive detector
Inject test solution (b) and reference solution (a). [131I]iodide is not less than 95 per cent of the total
radioactivity. Calculate the radioactivity of [131I] iodide.
Iodide. Determine by liquid chromatography (2.4.14).
Test solution (a). Dissolve a capsule under examination in 10 ml of water and filter.
Test solution (b). Dissolve a capsule under examination in water and filter. Dilute the filtrate with a 0.2 per cent
w/v solution of sodium hydroxide to a radioactive concentration suitable for the detector. Add an equal volume
of a solution containing 0.1 per cent w/v solution of potassium iodide, 0.2 per cent w/v solution of potassium
iodate and 1.0 per cent w/v solution of sodium hydrogen carbonate and mix.
Reference solution (a). Dilute 1 ml of a 0.00262 per cent w/v solution of potassium iodide to 10 ml with water.
Reference solution (b). Dilute 1 ml of a 0.00245 per cent w/v solution of potassium iodate to 10 ml with water.
Mix equal volumes of this solution and reference solution (a).
Blank solution. Prepare a solution containing 0.2 per cent w/v of each constituent stated on the label, apart from
iodide.
Chromatographic system
— a stainless steel column 25 cm x 4.0 mm packed with octadecylsilane bonded to porous silica (5 µm),
— column temperature 20° to 30°,
— mobile phase: dissolve 5.85 g of sodium chloride in 1000 ml of water, add 0.65 ml of octylamine and
adjust to pH 7.0 with dilute phosphoric acid; add 50 ml of acetonitrile and mix,
— flow rate. 1.5 ml per minute,
— spectrophotometer set at 220 nm and radioactivity detector connected in series,
— injection volume. 20 µl.
Inject reference solution (b) and the blank solution.
The relative retention time with reference to iodide (retention time is about 5 minutes) for iodate is 0.2 to 0.3. In
the chromatogram obtained with the blank solution, none of the peaks has a retention time similar to that of the
peak due to iodide. The test is not valid unless the resolution between the peaks due to iodide and iodate is not
less than 2.
Inject the test solution(a) and reference solution (a). Run the chromatogram for 12 minutes. In the
chromatogram obtained with test solution (a), the area of any secondary peak is not more than area of the
principal peak in the chromatogram obtained with reference solution (a) (20µg per capsule).
Labelling. The label states , in addition to the information specified under injections (1) the time and date of
calibration (2) the amount of 131I as total megabecquerels (millicuries) and concentration as megabecquerels
(millicuries) per ml at the time of calibration (3) the expiration date (4) the statement “ caution- radioactive
material”