Fundamental investigation of the dispersion caused by a change in diameter in nano liquid chromatography capillary tubing

Computational Fluid Dynamics Study of the Dispersion Caused by Capillary Misconnection in Nano-Flow Liquid Chromatography

“…The difference Δσ c 2 between both curves is then, following the approach in Moussa et al and according to eq , defined as the variance contribution originating from the transition . This difference is plotted in Figure d, showing that Δσ c 2 reaches a steady-state value when the band has migrated sufficiently far in the 2nd capillary to reach the point where all analytes have left the transition region.…”

“…It can be inferred that for cases where L c ≫ D c , Δσ c 2 will eventually be equal to the sum of the two Δσ c 2 values corresponding to the capillary diameter transition (one for a diverging transition and one for a converging transition, cf. ref ) plus the dispersion in the widened capillary between the inlet and outlet planes of the gap. However, verifying this for the largest L c case using the data from Moussa et al for a change in capillary diameter with a factor of 2, we see that the simulated Δσ c 2 value in this work is typically much smaller than the one obtained according to the aforementioned reasoning (0.044 vs 0.18 nL 2 for case 8) .…”

“…ref ) plus the dispersion in the widened capillary between the inlet and outlet planes of the gap. However, verifying this for the largest L c case using the data from Moussa et al for a change in capillary diameter with a factor of 2, we see that the simulated Δσ c 2 value in this work is typically much smaller than the one obtained according to the aforementioned reasoning (0.044 vs 0.18 nL 2 for case 8) . The fact that the actual dispersion is smaller than in this limiting case is because the latter case is only reached when the distance elapsed after a given change in diameter is longer than the distance needed for full radial equilibration.…”

“…In a previous computational fluid dynamics (CFD) study, we investigated the extra dispersion occurring at the connection between capillaries with different diameters. 25 In this study, the extra dispersion was reported as the increment in volumetric variance Δσ c 2 caused by the transition, i.e., Δσ c 2 was computed as the difference between the actually observed volumetric variance and the hypothetical volumetric variance that is obtained by summing the variances predicted by adding the Taylor−Aris solution determining the dispersion inside each of the two pieces of capillary separately. This was done assuming the dispersion in the 2nd capillary is independent from that in the first capillary.…”

“…In the present study, we investigate what happens if the connection is imperfect because it is well known from practice that a small difference in the quality of the connection can have a large effect on the quality of the separation, anyhow much larger than the dispersion values observed in our previous study. 25 The fact that in practice a small change in the quality of the connection can lead to large differences in extra-column band broadening is also the reason why the problem is investigated here using CFD because it is absolutely necessary to have exact control over and knowledge of each geometrical detail.…”