Technetium-99m radiochemical assay by rapid filtration: a superior alternative to chromatography

A new method for simultaneously measuring radiochemical purity and estimated lung trapping of colloidal technetium-99m (99mTc) radiopharmaceuticals is described. The method employs a small filtration device comprised of two stacked membrane filters, differing in membrane composition and in pore size, situated over a filtrate collection vial. Specifically, an 8-microns pore polycarbonate membrane filter is situated above a 0.22-microns pore mixed-cellulose-esters membrane filter. For assay, a diluted aliquot of radiopharmaceutical is passed through the filtration device. Technetium-99m radioactivity on the membranes and in the vial is then measured. The polycarbonate filter traps and quantitates lung-capillary-occluding particles. The mixed-cellulose-esters filter traps and quantitates radiocolloid particles irrespective of relative size. The filtrate contains free pertechnetate. Within 4 min, this method yields results that compare well with those achieved by conventional techniques. The method works equally well for large colloidal particles [( 99mTc]stannous colloid), intermediate-size particles [( 99mTc]sulfur colloid), and small-size particles [( 99mTc] antimony trisulfide colloid).