Preparation of density gradient solutions

Exposure (several months) of iodixanol solutions to direct sunlight will cause a slow release of iodine (solution turns yellow); OptiPrep should therefore be stored away from strong sunlight. 

On standing, iodixanol may "settle out" of concentrated solutions, which should be well mixed before use. 3. Osmolality The observed osmolality of OptiPrep depends on the mode of measurement (vapour pressure or freezing point); moreover the situation is complicated by the tendency of the iodixanol molecules to associate non-covalently in a concentrated aqueous solution. 

Measured values for its osmolality are thus lower than might be expected. Importantly however, when OptiPrep is diluted with a buffered isoosmotic solution, the iodixanol oligomers dissociate and all dilutions are isoosmotic. Under normal operating conditions therefore OptiPrep behaves as if it had an osmolality of approx 290 mOsm.