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Theoretical and experimental investigation of new possibilities to improve separation power and analysis time of chromatographic processes

vrijdag, 25 mei, 2012 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
Gebouw D
Promotiezaal D.2.01
Matthias Verstraeten
doctoraatsverdediging

Chromatography is the general term used for a class of separation techniques allowing to separate
the different components present in a given mixture. Chromatographic techniques are based on the
difference in velocity between components having a specific affinity for one of the two phases
used, one stationary (stationary phase) and one mobile (mobile phase). In high pressure liquid
chromatography or HPLC, the stationary phase is a solid and the mobile phase consists of a liquid,
which can be either a pure solvent or a mixture. This liquid is forced through a chromatographic
packed bed of the stationary phase by using high pressures up to 1200 bar.

In this doctoral thesis, a first research line aimed at investigating the effect of running a mobile
phase gradient under constant pressure instead of the customary constant flow rate mode. A
mobile phase gradient leads to a higher separation performance and is applied by mixing two
solvents inline and changing their composition from a weak solvent (high retention) to a strong
eluent (low retention). However, the maximal viscosity of the solvent mixture is only reached for a
short instance during a mobile phase gradient when keeping the flow rate constant, which thus
makes suboptimal use of the available pressure. When operating at a constant pressure, the flow
rate will vary and the average flow rate will be higher compared to the constant flow rate, leading to
a distinct time saving up to 20 or even 30%. Moreover, when applying the same mobile phase
gradient program in volumetric units, the same separation is obtained and identical area count and
reproducibility are achieved.

The second research line aimed at investigating the possibility to strongly retain (trap) and
remobilize components. Trapping is obtained by coupling the column with a fused silica capillary
packed with a porous graphitic carbon particles as stationary phase, which has a much higher
retention compared to the traditional silica-bonded stationary phases. The remobilization is
achieved by applying a fast temperature pulse using the Low-Thermal Mass LC system (LTMLC),
for which the heating properties were experimentally and numerically investigated. It was found
that when the molecules are trapped, they are locally concentrated at the interface of the trapping
material and an enhanced peak is detected once the components are remobilized. When applying
the heating periodically, the thermal modulation interface can also serve as an injector for the
secondary column. Furthermore, general design rules for the trapping segment of this interface are
given.

These new findings contribute to the development and innovation in chromatographic processes
and allow a higher separation power, a shorter analysis time and an enhanced sensitivity.