Page 5 - BR20828_E Accucore 0713S
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In the past decade there has been
continuous drive to develop
chromatographic stationary phases to
perform fast HPLC separations, as sample
throughput can be increased and therefore
cost per sample reduced. The theory of
chromatography predicts that the efficiency
of a LC separation increases with decreasing
particle size. As such, most columns currently
used for fast HPLC are packed with particles
in the sub-2µm internal diameter region. The
small particle diameter improves the
separation kinetics and therefore efficiency,
but at the expense of increased operating
backpressure. A two-fold reduction in
particle size (d p ) doubles efficiency (N is
proportional to 1/d p ), and produces
therefore a 40% fold increase in resolution
(resolution is proportional to the square root
of N). However, it also results in a four-fold
increase in pressure drop across the column
as pressure is inversely proportional the
square of d p . Additionally, sub-2µm particle
packed columns are generally run at high
linear velocities as these produce higher
efficiencies; consequently the HPLC
equipment has to be able to operate at
pressures in excess of the conventional 400
bar, unless very short column lengths
(< 50mm) are used. While a number of
manufacturers produce such HPLC
equipment, for laboratories that do not have
the financial luxury of being able to purchase
new instrumentation these columns are not
an option.
Manufacturers typically provide sub-2µm
particles in a fully porous format. The use of
partially porous particles, with a diameter
between 2 and 3µm, is starting to gain
momentum, as these provide similar
performance to sub-2µm particles at
significantly lower column backpressures.
Pellicular particles of large diameters have
been around since the 1960’s [1], but it was
Jack Kirkland who in 2000 developed 5 µm
particles that had a 0.25µm thick porous layer
and 30 nm pores for the separation of large
molecules [2]. The idea behind this
development was to take advantage of the
smaller diffusion distance of the molecule in
the particle, as macromolecules have low
diffusivity. Further developments of the
technology have allowed the manufacture of
solid-core particles of sub-3µm total
diameter. The Thermo Scientific Accucore
uses Core Enhanced Technology to produce
a 2.6µm solid-core material with very tight
particle size distribution and advanced
bonding technology to functionalise the
surface. The particles in the new Accucore™
stationary phases can be described as a solid
silica core surrounded by a porous outer
layer. The very tight particle size distribution
of this material results in columns with high
permeability, and therefore for the same
nominal pressure Accucore gives better
separations than fully porous materials. The
solid-core and the well defined porous outer
layer provides shorter diffusion paths into the
stationary phase compared with those in fully
porous particles, which reduces band
broadening and therefore improves
separation efficiency. Additionally, the better
packing facilitated by the tight particle size
distribution reduces differences in the radial
diffusion path in the liquid mobile phase.
An Overview of Core Enhanced Technology
for Fast, High Efficiency HPLC
by Luisa Pereira, Thermo Fisher Scientific
Tudor Road, Runcorn, Cheshire WA7 1TA, UK
The chromatographic material described herein uses core enhanced technology to produce columns that offer fast and high efficiency
separations at pressures compatible with conventional HPLC equipment. The particles in these new stationary phases are not fully porous
but rather have a solid silica core surrounded by a porous outer layer. The very tight particle size distribution results in columns with high
permeability, and therefore ’bar for bar‘ this solid-core material gives higher performance separations than fully porous materials. This
paper gives an overview of the fundamentals of the dispersion process in chromatography and applies it to the use of solid-core particles
in the separation mechanism, illustrating the benefits of this type of particle in fast, high efficiency separations. Column selection based
on selectivity, method transfer and the advantages that this technology has to offer in terms of column robustness are also reported.
Figure 1: Particle evolution: packing materials have changed from large pellicular particles via smaller
totally porous particles to spherical particles with diameters of less than 2
µ
m, to 2.6
µ
m solid-core particles
