Page 26 - BR20828_E Accucore 0713S

Equation 2
where E = impedance
ΔP = pressure drop
t = dead time of chromatographic system
η = kinematic viscosity of mobile phase
N = efficiency
In kinetic plots, the linear velocity, conventionally plotted
on the x-axis in the van Deemeter plot, is transformed
into the pressure drop limited plate number. Using a
maximum pressure drop for the system, any experimental
set of data of HETP- linear velocity obtained in a column
with arbitrary length and pressure drop can be trans-
formed into a projected efficiency (N)-t 0. This represents
the plate number and t0-time, which could be obtained if
the same chromatographic support was used in a column
that was long enough to provide the maximum allowed
inlet pressure for the given linear velocity.
The conventional approach to compare the chromato-
graphic performance of columns is to plot normalized
efficiency (HETP - height equivalent to a theoretical plate)
as a function of mobile phase flow rate or linear velocity,
often referred to as a van Deemter plot. This approach
does have limitations, since it does not account for
analysis time or pressure restrictions of the chromato-
graphic system. Kinetic plots [1] are an alternative method
of plotting the same experimental data that allow other
parameters, such as pressure, to be incorporated.
Therefore, we can infer the kinetic performance limits of
the tested chromatographic materials. There are a variety
of ways in which this data can be presented, and all of
these plots are referred to as kinetic plots. In one of
the most useful forms of kinetic plots, a term called
impedance is used. Impedance (Equation 2) defines the
resistance a compound is subjected to as it moves down
the column, relative to the performance of that column.
This term gives a true measure of the performance of the
column as it incorporates efficiency, time, and pressure,
which are critical practical considerations of a chromato-
graphic separation.
2
Figure 1: Comparison of column pressure for Accucore and competitor solid core columns.
All columns: 100 x 2.1 mm; test conditions: mobile phase water / acetonitrile (50:50 v/v), column temperature: 30 °C.
E =
∆P t
N η 2
∆P = a η F L (1 - ) 2
d 2
c d 2
p 33
i
3i
Pressure (Bar)
Flow rate (µL/min)
0
100
200
300
400
500
600
700
0 200 400 600 800 1000
Accucore RP-MS 2.6 µm
Nucleoshell RP-C18 2.7 µm
Poroshell 120 SB-C18 2.7 µm
Halo C18 2.7 µm
Kinetex C18 2.6 µm
Ascentic Express C18 2.7 µm
Sunshell C18 2.6 µm
Table 1: Columns used in this study
Material Particle Diameter Pore Diameter Bonded Phase Dimensions
Accucore 2.6 µm 80 Å RP-MS 100 x 2.1 mm
Kinetex® 2.6 µm 100 Å C18 100 x 2.1 mm
Poroshell® 120 2.7 µm 120 Å SB-C18 100 x 2.1 mm
Ascentis® Express 2.7 µm 90 Å C18 100 x 2.1 mm
Halo® 2.7 µm 90 Å C18 100 x 2.1 mm
Nucleoshell® 2.7 µm 90 Å RP 18 100 x 2 mm
SunShell ® 2.7 µm 90 Å C18 100 x 2.1 mm