Abstract
As column volumes continue to decrease, extra-column band broadening has become an increasingly important consideration when determining column performance. Combined contributions due to the injector and connecting tubing in a capillary LC system were measured and found to be larger than expected by Taylor-Aris theory. Variance from sigma-type and tau-type broadening was isolated from eluted peaks using the Foley-Dorsey Exponentially Modified Gaussian peak fitting model and confirmed with computational fluid dynamics. It was found that the tau-type contributions were the main cause for the excessive broadening because of poorly-swept volumes at the connection between the injector and tubing. To reduce tau-type contributions (and peak tailing), a timed pinch mode could be used for analyte injection.
Highlights
Since the advent of ultra-high pressure liquid chromatography (UHPLC), particle sizes and column diameters have decreased, leading to smaller column volumes
Similar to previous eras when column technology began to exceed the limitations of commercial equipment [12,13], extra-column band broadening (ECBB) is seeing increasing attention as an important factor that needs to be accounted for and reduced as much as possible [14,15,16,17,18]
In the early development of capillary UHPLC, home-built instruments were constructed that eliminated most instrumental effects and gave a direct measure of column efficiency while allowing for backpressures in excess of 50,000 psi [22,23,24,25,26,27]. These types of systems are excellent for comparing packing methods or particle types, but most commercial capillary and nano-UHPLC instruments in use today sacrifice these extremely high pressures and negligible extra-column volume for ease of use and range of application
Summary
Since the advent of ultra-high pressure liquid chromatography (UHPLC), particle sizes and column diameters have decreased, leading to smaller column (and, peak) volumes. In the early development of capillary UHPLC, home-built instruments were constructed that eliminated most instrumental effects and gave a direct measure of column efficiency while allowing for backpressures in excess of 50,000 psi [22,23,24,25,26,27] These types of systems are excellent for comparing packing methods or particle types, but most commercial capillary and nano-UHPLC instruments in use today sacrifice these extremely high pressures and negligible extra-column volume for ease of use and range of application (gradient modes, detection methods, etc.). The impacts of a timed pinch injection mode on the reduction of injector broadening and the effects on peak shape when very short tubes are used are discussed
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