Removal of the 2.2.2 cryptand (kryptofix 2.2.2™) from ¹⁸FDG by cation exchange

The 2.2.2 cryptand [4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-(8.8.8)-hexacosane] was trapped efficiently on Dowex AG50W-X8 (100-200 mesh) cation exchange resin. The concentration of the 2.2.2 cryptand in water with 0.1-2% methanol, or in 1 N HCl, was decreased by a factor of >4000 using 1 mL (1.7 mequiv.) of AG50W-X8 and a flow rate of approx. 2 mL/min. K⁺, Cs⁺, Ag⁺ and Ba²⁺ forms were about equal in their ability to remove the 2.2.2 cryptand. A disposable cartridge containing 1 mL of hydrogen form resin was inserted into our automated ¹⁸FDG system so that the hydrolysate (in 2 cm³ of 1 N HCl) would pass through the cartridge before final purification. No cryptand was detected in the final product as determined by TLC with idoplantinate visualization. The detection limit was 2.5 μg/mL. Less than 3% of the total starting radioactivity was retained by the cation column. Quality assurance tests including apyrogenicity, sterility, radiochemical purity, carbohydrate composition and pH were not compromised by the incorporation of the cryptand removal cartridge.