Self-Assembled Monolayers (SAM) are supramolecular organizates resembling, in some respects, the well-known Langmuir-Blodgett (LB) built-up films while displaying other distinct and rather Special features. Much of the interest in SAM stems from their potential in wide range of scientific and technological applications. The first application of SAM in chromatographic separation science was developed at the University of Delaware by Fatunmbi and Wirth. The bonding technique allows ordered monolayers of functional molecules to be chemically immobilized on solid substrates, such as, silica and alumina.
The technique of bonding was termed â€œhorizontal polymerizationâ€ due to the fact that there is significant Si-O-Si bridging parallel to the silica substrate. This is achieved by reaction of trifunctional silanizing agent with the silica substrate under anhydrous condition, except for a monolayer of water on silica. This contrasts with conventional polymerization of trifunctional silanes, referred to as â€œvertical polymerization,â€ where water is deliberately added to polymerize the reagents before attachment to the surface. The key structural difference here is that horizontal polymerization provides much higher ligand density at the silica surface boundary.
The bonding chemistry utilized for chromatographic applications results in a monolayer coverage with typical thickness in the range of 6-22 Å, depending on the length of the attached ligand. For example, when a C18 ligand is attached, a film thickness of about 22 Å is obtained. Thickness in this range ensures bonding of the ligand both in and around the substrate material without blocking of the pores. Results from the relaxation time measurements, using solid state nuclear magnetic resonance spectroscopy (NMR), showed that the spacer molecules are evenly dispersed within the functional ligand and are not clumped together.
SAM is applicable to virtually all types of functional groups
SMT columns for reversed-phase chromatography include SMT OD C18, SMT O C8, SMT Elite C18, SMT Elite C8, SMT ODL, SMT OL, SMT MEB (including C1, C2, and C4), SMT C30, SMT Hexyl C6, SMT C12, SMT C3, SMT C5, SMT PHEN1 Phenyl, SMT AquSep (ODAQ), SMT Urea, SMT ChiralSep, SMT CIB and other mixed phases.
SMT offers many other columns for ion exchange chromatography including SMT SAX, SMT WAX, SMT SCX, SMT WCX, SMT DEAE, SMT MetalSep. Unlike polymer-based counterparts, these columns are silica-based and are mechanically stable at higher chromatographic pressures.
SMT offers packing materials for large-scale purification and Solid Phase Extraction (SPE) processes. Essentially all SMT analytical column packing materials are offered in large particle sizes at significantly reduced prices for process scale column packings and low pressure bulk purifications. Please refer to our bulk packing materials for these products.