The silanol (-Si-OH) groups that remain on the surface of a packing after a phase is chemically bonded onto its surface. These silanol groups may not be accessible to the reacting bulky organosilane (e.g., octadecyldimethylchlorosilane) but may be accessible to small polar compounds. Often they are removed by endcapping with a small organosilane such as trimethylchlorosilane. See Endcapping.