silica gel - the most commonly used adsorbent in liquid chromatography. It has an amorphous structure, is porous, and consists of siloxane and silanol groups. It is used as a bare packing for normal-phase, as the support in liquid-liquid chromatography or for chemically bonded phases, and, with various pore sizes, as packing in size-exclusion chromatography. Micro-particulate silicas of 5- and 10-Ám average particle diameter are used in HPLC.

See silica.

siloxane - the Si-O-Si bond. A principal bond found in silica gel or for attachment of a silylated compound or ligand for controlling the surface chemistry. Stable except at high pH values.

See surface chemistry.

silylation - a chemical reaction involving a silane reagent such as trimethyl chlorosilane (TMS); used to silanize or deactivate active sites found in samples on solid support surfaces and even on glass tubing.

single-piston pump - see "reciprocating piston pump".

See HPLC pump.