The mobile phase is composed primarily of supercritical carbon dioxide, but since CO on its own is too non-polar to effectively elute many analytes, cosolvents are added to modify the mobile phase polarity.  Cosolvents are typically simple alcohols like methanol, ethanol, or isopropyl alcohol.  Other solvents such as acetonitrile, chloroform, or ethyl acetate can be used as modifiers.  For food-grade materials, the selected cosolvent is often ethanol or ethyl acetate, both of which are generally recognized as safe (GRAS).  The solvent limitations are system and column based.