What Pressure to Expect from the
Thermo Scientific Accucore HPLC Columns?
Luisa Pereira, Thermo Fisher Scientific, Runcorn, Cheshire, UK
Technical Note 20542
Key Words
Fast LC, Pressure, Solid Core Particles, Sub-2 μm Particles,
Core Enhanced Technology
Abstract
This technical note discusses the effect that column length, internal
diameter (ID), particle size, and mobile phase flow rate and viscosity
have on the operating pressure in HPLC. Comparison data on the
measured pressure for solid core and fully porous particle packed
columns (5, 3 and sub-2 µm) is shown.
Introduction
Most stationary phases currently used for fast HPLC have
a fully porous particle support, with diameters in the
sub-2 µm region. The small particle diameter improves
the separation kinetics and therefore efficiency, but at
the expense of operating backpressure. Additionally,
sub-2 µm 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 (<50 mm) are used.
Partially porous particles, with a diameter between 2
and 3 µm, provide similar performance to sub-2 µm
particles at significantly lower column backpressures.
The Thermo Scientific
™
Accucore
™
HPLC column range
uses Core Enhanced Technology
™
to produce a 2.6 µm
solid-core material with a very tight particle size
distribution. This results in columns with high perme-
ability, and therefore “bar for bar” Accucore columns
produce improved separations when compared to fully
porous materials.
Equation 1 shows the dependency of pressure drop across
the column on particle size and flow rate, discussed above.
Pressure is directly proportional to column length,
flow rate and mobile phase viscosity and inversely
proportional to the square of the particle size diameter
and the square of the column internal diameter.
Equation 1:
Where:
D
P – pressure drop across the column
e
i
– interstitial porosity of the packed bed
F – flow rate through the column
L – length of the column
h
– viscosity of the mobile phase
d
p
– particle diameter
d
c
– column internal diameter
Other operating parameters that will have an impact on
pressure are the ID and length of the connecting tubing
in the LC system, detector set-up parameters such as
flow cell volume in UV or the ID and length of the
capillary components in ESI or APCI sources in LC/MS.
Pressure can be a useful symptom when troubleshooting
LC systems.
PRESSURE
D
P = 236
(1 –
e
i
)
2
F L
h
e
i
3
d
c
2
d
p
2
1...,5,6,7,8,9,10,11,12,13,14 16,17,18,19,20,21,22,23,24,25,...58