Technical data

18 Agilent 1290 Infinity LC System Manual and Quick Reference
1 Introduction to Ultra-High Performance Liquid Chromatography
Frictional Heating
Frictional Heating
Forcing mobile phase through the column at higher pressure and higher flow
rates generates heat. The resulting temperature gradients (radial and
longitudinal) can have an impact on the column efficiency.
where F is the flow rate and p is the pressure.
Powerful column thermostatting (for example, using a water bath) generates a
strong radial temperature gradient, which leads to significant loss in column
efficiency. Still-air column thermostatting reduces the radial temperature
gradient and therefore reduces the efficiency losses, but a higher column
outlet temperature has to be accepted. The raised temperature may have an
effect on selectivity. At lower back-pressure, performance losses due to
frictional heat are minimized so that 4.6 or 3 mm inner diameter sub-2-micron
columns still deliver superior efficiencies compared with the respective
2.1 mm inner diameter columns.
An example of a gradient method transfer to a 2.1 mm i.d. STM column in
which the separation has been speeded up is shown in Figure 9 on page 19.
The initial run on the 2.1 mm column was at a flow rate of 0.22 ml/min
generating 380 bar pressure at a temperature setting of 37 °C with all peaks
separated in 12.5 min (chromatogram not shown). The flow was increased to
0.66 ml/min and the gradient times adjusted downwards by a factor of three
generating 1020 bar pressure with all peaks eluted in 4.2 min (Figure 9 on
page 19 above). This should give the same separation but a loss of resolution
can be seen between peaks 7 and 8 and between 5 and the main peak and this
is due to heating in the column changing the selectivity for these compounds.
It was found that running the column thermostat at 5 °C lower was sufficient
to offset the heating effect inside the column and restore the separation
(Figure 9 on page 19 below). The pressure increased to 1070 bar which also
indicates that the in-column temperature was lower.