How have UHPLC systems advanced in recent years?
One of the key benefits of newer UHPLC systems is that they can offer combined HPLC/UHPLC operation without sacrificing performance.
Although several combined HPLC/UHPLC systems have been available in the market for some time, their main drawback has been
loss of performance when operating outside the specific set of conditions they have been optimised for.1 Another limitation has been the lack of quaternary capabilities. Such capabilities require low pressure mixing and in the
past, low pressure mixing demanded larger delay (dwell) volumes for optimum performance, which is detrimental for true UHPLC
operation to achieve optimum performance and allow proper solvent mixing.
With newly developed pump technology, however, this is no longer the case. This technology employs unique force sensors to
modulate pumping efficiency based on assessed mobile phase compressibility; thereby enabling the delivery of accurate and
reproducible gradients with extremely low delay volumes. The force sensors employed in these pumps measure the actual force
that is needed to move each piston and can be used to determine compressibility of the displaced solvent in real-time. As
such, variations in compressibility caused by changes in mobile phase composition and temperature, etc., can be accounted
for and compensated during each individual piston stroke. The end result is volumetric, virtually pulsation free flow from
the pump over its complete dynamic working range. The high stability of flow and pressure also eliminates the need for a pulse
dampening device, which increases ease of use. Overall, the technology has helped increase the accuracy and reliability in
pump performance under all operating conditions.
Some newly developed systems also offer quaternary mixing capabilities, which are extremely useful when developing chromatographic
methods and when more than two solvents are needed to achieve adequate chromatographic resolution, such as when working with
complex samples.
Sergio Guazzotti is Senior Global Product Marketing Manager, Liquid Chromatography at Thermo Fisher Scientific
Reference
1. Thermo Fisher, Application Note 405: Analysis of Simvastatin Tablets by High Speed LC (2007).
http://www.thermo.com/appnotes
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