They are essentially non-specific and non-porous sorbents with a surface area of about 100 or 200 m 2 g−1[24,25]. Because of the presence of positively charged chemical heterogeneities on their surface, they can be considered to be both reversed-phase (RP) sorbents and anion exchangers. Therefore GCB exhibits the advantage of high affinity for organic acidic compounds, and could be a suitable adsorbent for our purpose of isolating PFOSs and PFOAs from milk.