Research & Development

comprised of inert bridged-ethyl hybrid (BEH) particles, similar in composition to the standard ACQUITY BEH columns used today. By modifying the surface of the particles with a trimethylsilane reagent, residual surface silanols are masked, and thus provide an inert and non-retentive chromatographic surface for use with organic mobile phases. In the case where aqueous mobile phases are employed, unbonded materials provide the best chromatographic media due to the inherent low surface acidity of BEH particles. To achieve the desired selectivity, the pore volume of the media was increased by almost two-fold compared to the traditional ACQUITY UPLC media. Despite the significantly greater pore volume, particles still maintain the mechanical stability necessary for operation under UPLC conditions. Furthermore, the ACQUITY APC columns comprise well-packed beds of sub-3-micron, high-pore-volume particles, with mean pore sizes of 45 Å, 125 Å, 200 Å, and 450 Å. This range of pore sizes enables separation of a broad range of molecular weights. Combining the column/particle technology with the ability to operate at higher flow rates, run times can be up to 10 times shorter than traditional SEC, without any sacrifice in chromatographic resolution.

A challenging application is the separation of low molecular weight
oligomers. Synthetic oligomers are used for numerous applications:
lubricants, plasticizers, coatings, and as intermediate prepolymers. The
goal in oligomeric SEC is to resolve the individual components from
each other, typically to quantitate the total oligomeric species. The
quality of the oligomer separation can be impacted by both the band-
spread of the chromatographic system as well as the efficiency of the
liquid chromatography (LC) column.

–Ed Bouvier, Manager, Advanced Materials Research Group, Mia Summers, Principal Applications Chemist, and Michael O’Leary, Principal Scientist, Chemical Materials Business Operations, Waters Corp., Milford, Mass.

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