Polyethylene glycol (PEG) has low toxicity and is used in a variety of products (creams, laxatives, lubricants). When attached to various protein medications, polyethylene glycol allows a slowed clearance of the carried protein from the blood. This makes for a longer acting medicinal effect, reduces toxicity, and allows longer dosing intervals. HILIC separation of polyethylene glycol can be used to determine polyethylene glycol content in various formulations using ELSD, RI detection, or LC/MS detection. HPLC separation of oligomers can be achieved by changing amount of acetonitrile or buffer pH.