Emerging Trend for LC-SPE Sorbents
“We are starting to see the use of LC-SPE (solid-phase extraction) sorbents to perform separations in the protein and proteomics areas. It is an emerging trend,” comments Rob Freeman, business manager, chromatography, SGE Analytical Science.
Conventional SPE started with disks and tubes for sample volumes from 50 mL to 1 L, using either gravity or a vacuum to move the solvent through the large sorbent bed. SGE Analytical Science has combined the advantages of SPE with automation by developing a digital syringe, eVol®, with an embedded miniaturized SPE cartridge.
MEPS™, micro-extraction by packed sorbent, incorporates a cartridge, which holds a few mg of sorbent, into a removable needle syringe. This solid-phase-extraction technique can be used for protein sample preparation manually, just like a standard syringe, or interfaced with gas or liquid chromatography systems through an autosampler. In addition, recently, the combination of eVol and MEPS was used to infuse extracted analytes directly into the MS-ESI (electrospray ionization) source, without any additional modifications.
The specific sorbents and particle pore sizes (pore size corresponds to surface area), impact the sizes of proteins and peptides that are retained. The typical MEPS pore size is 120 angstroms, which is larger than the conventional SPE pore sizes of 60–80 angstroms.
The miniaturized format works with small-volume biological samples, 10–1,000 µL, improves efficiencies, and virtually eliminates solvent use and waste.
The sorbent, a spherical silica particle with an attached polymer such as C4, C8, or C18, separates and extracts through hydrophobicity and retentive interaction. SGE Analytical Science is working on extending MEPS capabilities for protein sample preparation using polymer monoliths in collaboration with Emily Hilder, Ph.D., at the Australian Centre for Research on Separation Science.