Modulation interfaces employing sample loops are applied in many hyphenated separations such as two-dimensional liquid chromatography (2D-LC). When the first-dimension effluent in 2D-LC is eluted from the modulation loop, dispersion effects occur due to differences in the laminar flow velocity of the filling and emptying flow. These effects were recently studied by Moussa et al. whom recommended the use of coiled loops to promote radial diffusion and reduce this effect. In the 1980s, Coq et al. investigated the use of packed loops, which also promote radial diffusion, in large volume injection 1D-LC. Unfortunately, this concept was never investigated in the context of 2D-LC modulation.
In their study CAST scientist Wouter Knol evaluated use of packed loops in 2D-LC modulation and compares them to unpacked coiled and uncoiled modulation loops [1]. The work was conducted under the supervision of Prof. Ron Peters and Dr. Bob Pirok. The effect of the solvents, loop volume, differences in filling and emptying rates, and loop elution direction on the elution profile were investigated.
To pragmatically quantify elution profile characteristics, Knol employed statistical moments. Decreased dispersion was observed in all cases for the packed loops compared to unpacked loops and unpacked coiled loops. In particular for larger loop volumes the dispersion was reduced significantly. Furthermore, countercurrent elution resulted in narrower elution profiles in all cases compared to concurrent elution.
Knol found that packed modulation loops are of high interested when analytes are not refocussed in the second-dimension separation (e.g. for size-exclusion chromatography). One additional observation was that the work suggested that the use of packed loops may aid in prevention of loop overfilling.
This study was conducted in the context of the UNMATCHED project which received funding from BASF, DSM and Nouryon, as well as the Dutch Research Council (NWO). The work was published in Journal of Chromatography A and can be accessed for free here.
