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Effect of the pressure on pre-column sample dispersion theory, experiments, and practical consequences
Fabrice Gritti1, Georges Guiochon1
1Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA.
Journal of Chromatography. A
|June 14, 2014
Summary
High system pressure significantly increases peak variance in chromatography, impacting column efficiency measurements. Accurate efficiency requires accounting for pressure-dependent dispersion, not just flow rate.
Area of Science:
- Analytical Chemistry
- Chromatography
Background:
- Dispersion in open tubes is influenced by pressure.
- Previous models by Aris and Taylor (1953) and Alizadeh (1980) provide theoretical frameworks.
- Very high pressure liquid chromatography (vHPLC) operates at elevated pressures.
Purpose of the Study:
- To investigate the theoretical and experimental effects of system pressure on compound dispersion in open tubes.
- To evaluate the impact of pressure on column efficiency measurements in vHPLC.
- To demonstrate the limitations of using zero dead volume connectors for accurate efficiency determination.
Main Methods:
- Theoretical modeling based on Aris-Taylor and Alizadeh dispersion models.
- Experimental investigation using 0.508 and 1.016 mm i.d. × 50 cm open tubes.
- System pressure varied from <20 to ~1,000 bar using upstream capillary resistances in a vHPLC system.
Main Results:
- Peak variance increases linearly with increasing pressure within the tube.
- A 7% relative increase in peak variance per 100 bar increment was observed.
- Apparent column efficiency is affected by pre-column pressure, independent of flow rate effects.
Conclusions:
- Accurate column efficiency measurements must consider pressure-dependent extra-column contributions.
- Replacing columns with zero dead volume connectors leads to inaccurate efficiency data due to pressure differences.
- Increasing pre-column pressure affects measured column efficiency, with significant decreases expected for certain retention factors.
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