Colorimetric determination of tin(II) levels in 99mTc labelling kits

A rapid quantitative test for determination of stannous tin in kit preparations is described. After addition of phosphomolybdate a blue colour is measured at 700 nm. Sn2+ levels in pyrophosphate, MDP, DTPA, diethyl HIDA, dimethyl HIDA, glucoheptonate, phytate and tin colloid kits were determined. In many kits these levels proved to be rather low. Results from the colorimetric test were comparable with those obtained by iodometric titration. During exposure to the air by extensive stirring, Sn2+ preparations showed rapid deterioration which could be prevented by adding ascorbic acid. This simple test is a valuable method to determine Sn2+ levels in many kit preparations and can be useful in the investigation of factors that contribute to the decrease of the Sn2+ content.