Tag: Wouter Knol

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Packed loops may reduce dispersion in 2D-LC

Packed particles may reduce dispersion in 2D-LC
Packed particles may reduce dispersion in 2D-LC

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.

Packed loops may reduce dispersion in 2D-LC
Figure 1. Schematic representation of the experiential setup in the loop filling and emptying valve position. Along with the packing of loops, the effect of coiling was also investigated. Reproduced with permission from [1].

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.

Packed loops may reduce dispersion in 2D-LC
Figure 2. Schematic representation of the experiential setup in the loop filling and emptying valve position. Along with the packing of loops, the effect of coiling was also investigated. Reproduced with permission from [1].

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.

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Detection Challenges in Polymer Analysis with LC

With their large distributions culminating in wide envelopes of – almost exclusively – co-eluting peaks, polymers certainly present a unique challenge relative to the analysis of small molecules. If anything, this challenge has spurred innovations which have also benefited other fields. A good example has been the work on polymer analysis with 2D-LC in the first years of this millennium, which have certainly contributed to recent developments on the technique [1,2].

In his review, Wouter Knol (Van ‘t Hoff Institute for Molecular Sciences) reviews another research area which offers a lot of room for innovations: detection. Together with the co-authors, Knol provided an exhaustive overview of applications of detection techniques in LC for polymer analysis. For each detection technique, notable recent applications are discussed and the authors distilled the key advantages and disadvantages of each approach.

One particularly useful trait of the review is this table which summarizes all key strengths and weaknesses of each detection technique employed for LC in polymer analysis. Reprinted with permission from [3].

Knol and co-workers noted that promising approaches receive surprising attention in recent literature. He concluded that the opportunities deserve more attention. You can download and read the paper, which was published open-access in the special Reviews 2021 issue of Journal of Separation Sciences, here.

Example of a separation of complex polyether polyols with LC×LC-MS by Groeneveld et al. showing a clear structure based on the number of ethylene oxide/propylene oxide units in the polymer. Reprinted with permission from [4].

References

[1] Recent Developments in Two-Dimensional Liquid Chromatography: Fundamental Improvements for Practical Applications
B.W.J. Pirok, D.R. Stoll and P.J. Schoenmakers, Anal. Chem., 2019, 91(1), 240-263, DOI: 10.1021/acs.analchem.8b04841

[2] Comprehensive Two-Dimensional Ultrahigh-Pressure Liquid Chromatography for Separations of Polymers E. Uliyanchenko, P.J.C.H. Cools, Sj. van der Wal and P. J. Schoenmakers, Anal. Chem. 2012, 84, 18, 7802–7809, DOI: 10.1021/ac3011582

[3] Detection challenges in quantitative polymer analysis by liquid chromatography, W.C. Knol, B.W.J. Pirok, and R.A.H. Peters, J. Sep. Sci. 2020, DOI: 10.1002/jssc.202000768

[4] Characterization of complex polyether polyols using comprehensive two-dimensional liquid chromatography hyphenated to high-resolution mass spectrometry G. Groeneveld, M.N. Dunkle, M. Rinken, A.F.G. Gargano, A. de Niet, M. Pursch, E.P.C. Mes, and P.J. Schoenmakers, J. Chromatogr. A, 1569, 2018,  128-138, DOI: 10.1016/j.chroma.2018.07.054

Wouter Knol was a PhD candidate in the group of Peter Schoenmakers and Bob Pirok. He worked in the UNMATCHED project in Amsterdam and mainly focuses on techniques to determine the sequence distribution of polymers.

You can read more about him on our Team page.