disclosed herein is a composition and method for sample preparation of proteins for their size separation by electrophoresis , suitable for molecular - weight determination of proteins in the range between about 14 , 000 and 500 , 000 . in an embodiment , proteins , particularly those exhibiting biased migration , are modified to change their intrinsic charge , or carbohydrate component to improve accuracy of their molecular weights as determined by electrophoretic size separation via their interaction with ionic surfactants . in a preferred embodiment , the proteins are carbamylated with potassium cyanate and their carbohydrate components are oxidized with sodium periodate .