“…A family of restricted access sorbents, namely alkyl diol silica (ADS), belonging to the group of internal surface reversedphase (ISRP) supports, has been applied successively for on-line sample clean-up prior to the determination of compounds in different biological matrices [15][16][17][18][19]. After direct injection of biological samples, macromolecules, such as proteins, are flushed to the waste due to an appropriate pore diameter (about 6 nm) of the silica particles, while low molecular-mass compounds can penetrate into the pores and be retained by interaction with butyryl (C 4 ), capryoyl (C 8 ) or stearoyl (C 18 ) moieties bonded to the inner surface. The molecular weight cut-off is approximately 15 kDa.…”