8 May / June 2014
UHPLC or Core-Shell Which is the Winner?
Mark Woodruff
Fortis Technologies 45 Coalbrookdale Road, Clayhill Business Park, Neston, Cheshire, CH64 3UG Tel: +44 (0) 151 336 2266 email:
markwoodruff@fortis-technologies.com
www.fortis-technologies.com
Commercial UHPLC technology burst onto the scene in 2004. It was the new technology that was going to move chromatography forward, however was it really new? The sceptic in me says no, we had moved from 5µm particles to 3µm particles 10-15 years previously, moving down to the next particle size, i.e. sub 2µm was the next logical step and this is what UHPLC essentially was. An LC system with extreme low dead volume and ‘bolt on high pressure’. I say ‘bolt on high pressure’ because what does the pressure do for our chromatography, it doesn’t give us more efficiency, resolution, selectivity or speed, it allows us to use smaller particles, which then does give us greater efficiency and subsequent speed and resolution.
Now in the last couple of years a ‘new’ technology core-shell (fused-core, solid- core, superfi cially porous particles, SPP, call it what you will) has now peaked everybody’s interest! Again I highlight the word ‘new’ since these types of particles were actually fi rst discussed and commercialised back in the 1970’s by Zorbax technologies.
Core-shell technology uses a solid silica core and a porous outer silica shell to provide the same high effi ciency separations as the sub 2µm UHPLC particles, but with potentially lower backpressure. Current theory has the effi ciency generated by these particles arising largely from the mono disperse nature of the solid core coupled with the reduced void volume of the column and to a lesser extent from the reduced mass transfer that takes place during the separation. As with all technology there will be differing manufacture processes in the production of these core-shells and therefore a potentially wide range of physical characteristics, resulting in a range of pressures, hydrophobicities and peak shapes (Figure 1).
Lifetime
Obviously characteristics such as backpressure then have a big impact on the lifetime of columns, along with the linear velocities that can be achieved (Figure 2).
Does backpressure work totally against UHPLC particles, not really, if the manufacturer has done a good job then the sub 2µm particle should withstand the elevated pressures. As an example, at Fortis Technologies we pack our 1.7µm particles at >1400bar (approx.20,000 psi pressure) ensuring that the packed bed is
Figure 1. (Backpressure of 2 commercial core-shells vs fully porous particles)
Figure 2. Van-Deemter curve for 2 core-shell, highlights how 65% greater linear velocity (Uo)can be achieved for the same backpressure, giving a greater usable fl ow rate range.
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