40 Buyers’ Guide 2021
µ-Pillar Array Column – an Innovative Approach for the Separation and Characterisation of Complex Biological Samples
R. van Ling, P. Jacobs
PharmaFluidics, Belgium, Technologiepark-Zwijnaarde 82, 9052 Ghent
robert.vanling@
pharmafluidics.com
Abstract
During the last few years, the µ-pillar array column has had an impact in low flow LC/MS applications. Here we will discuss this innovative approach to produce chromatographic columns, and the improvements this can offer for separation performance, reproducibility and robustness.
Introduction
Over the last decades, liquid chromatography (LC) has established itself as one of the most employed separation techniques in life sciences research, product development and quality control. The heart of the LC system is the separation column, where the sample compounds are separated from each other to facilitate the best possible detection and quantification.
One of the most visible developments in LC column technology is the continuous reduction of particle size. Many researchers will remember Waters introducing UPLC® or Ultra Performance Liquid Chromatography and the 1.7 µm fully porous silica particle columns [1], followed swiftly by other manufacturers, including Agilent, Phenomenex and Thermo Scientific, with their own sub-2 µm particle UHPLC (Ultra High Performance Liquid Chromatography) columns. In combination with the ongoing improvements in particle shape and purity, the smaller size allowed for more efficient separations with respect to resolution, speed and sensitivity. However, smaller particle size columns generate higher back pressures [2], requiring higher pump pressure capabilities. Traditional HPLC pumps provide an operating pressure of typically up to 6,000 psi or 420 bar, perfectly suited to run 3-5 µm particle columns. UHPLC pumps operate at significantly increased pressures, currently up to 22,000 psi or 1,500 bar [3]. Further UHPLC system optimisations, such as reduced gradient delay volumes, from solvent mixer to the head of the column, and extra-column volumes, from the column to the detector, allow the sub-2 µm particle columns to demonstrate their optimal performance.
An alternative development resulted in the solid core particle, also known as fused-core or superficially porous particle. These particles
Figure 1. Overview of PharmaFluidics µ-pillar array (µPAC™) technology. (a) design of separation channel, (b) photomask, (c) silicon wafer, (d) µ-pillar bed after Deep Reactive Ion Etching (DRIE),(e) µ-pillars after porosification
are typically between 2-3 µm in diameter, with a non-porous core which is covered with a thin porous layer, providing increased separation efficiency and speed of analysis, without requiring as high a back
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