What is the difference between a monomeric and polymeric C18 bonded phase?
Chemically bonded alkyl phases can be prepared through various reactions, resulting in e.g. Si-O-C-, Si-N-C- or Si-O-Si-C- linkages (the first Si atom represents the silica surface). The hydrolytic stability of these bonded phase increases in the same order. Therefore, most commercial reversed phase HPLC packing materials today are prepared from alkylsilane reagents, which result in Si-O-Si-alkyl linkages, and are stable in aqueous/organic mobile phases from pH 2 to 7. Historically, trichloroalkylsilanes were first employed as alkyl bonding reagents in HPLC, as they were widely used in industry for the production of waxes and coatings, and are less expensive than di- and especially monochloroalkylsilanes. When a bonded phase is prepared from a monofunctional alkylsilane reagent, the reagent can only form a single bond with a surface silanol group. The resulting bonded phase is called a monomeric bonded phase, resembling a brush type phase, in which each of the bristles represents the s
