The following van Deemter graphs – where plate height, H, is plotted versus linear flow velocity - report the results of
this investigation.
With respect to the two solid core 2.6 μm particle size materials (Accucore150-Amide-HILIC and Accucore HILIC), it
can be seen above that the bare silica has a flatter profile (lower value of the C term in the van Deemter equation) and
hence a better preservation of high efficiency at high flow rates than the amide material. The optimum flow rate for
the bare silica (Accucore HILIC) is in the range of 0.9−1.7 mL/min; however, even above 1.7 mL/min efficiency is not
compromised as the increase in H is minimal.
The amide phase (Accucore150-Amide-HILIC) demonstrated an optimum flow rate range of 0.7−1.0 mL/min.
Within its optimal flow rate range, the bare silica phase demonstrated slightly lower H values (plate height) than the
amide material. Lower H values correspond to higher plate counts, making the bare silica material more efficient.
The zwitterionic phase (5 μm particle size) investigated showed a prominent variation in efficiency with flow rate, as
illustrated in the figure below:
18
The zwitterionic phase showed relatively high H and mass transfer term values. The minimum plate height is similar
to the values reported by McCalley [13] and Hemström and Irgum [1]. According to Hemström and Irgum, the relative
thickness of the zwitterionic interactive layer could be the major contributor to the high mass transfer term (although
the authors were referring to a polymeric rather than a monomeric coating).
From the van Deemter plot reported above, it can be seen that the best performance on the zwitterionic phase is
achieved at flow rates between 0.6−0.8 mL/min.
Columns:
Accucore 150-Amide-HILIC
Accucore HILIC
2.6 μm 100 × 4.6 mm
Mobile Phase:
90/10 acetonitrile/100 mM
ammonium formate (pH 3.5)
Sample:
atenolol
Column:
Syncronis HILIC
, 5 μm
100 × 4.6 mm
Mobile Phase:
90/10 acetonitrile/100 mM ammonium
formate (pH 3.5)
Sample:
atenolol
H ( m)
Linear velocity (mm/s)
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
0.5
0.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Accucore HILIC Accucore 150-Amide-HILIC
H ( m)
Linear velocity (mm/s)
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
3.5
Syncronis HILIC
Optimum
Flow Rate:
Accucore 150-Amide-HILIC
, 0.7−1.0 mL/min
Accucore HILIC
, 0.9−1.7 mL/min
Optimum
Flow Rate:
Syncronis HILIC
,
0.6−0.8 mL/min
