Hydrophilic interaction electrokinetic chromatography using bio‐based nanofillers

Abstract

Hydrophilic interaction (HI)-based separation like HILIC is effective for analyzing hydrophilic biological samples such as carbohydrates, peptides, and metabolites. To overcome the drawbacks of conventional HILIC such as large consumption of organic solvents and easy deterioration of the separation column, we developed HI electrokinetic chromatography (EKC) by employing bio-based nanomaterials as the hydrophilic pseudostationary phase. By mechanical/chemical treatments, cellulose, chitin, and chitosan were processed to 10-nm wide nanofibers/nanowhiskers (NFs/NWs), which are longer/shorter than 1000/200 nm, respectively. In HI-EKC of oligosaccharides using 0.001% uncharged cellulose NFs, strong interaction was observed for the large-size oligosaccharides with the retention factors (k) of up to 1.56, indicating a HILIC-mode interaction. In HI-EKC with 0.1% positively charged chitosan NFs, benzenedisulfonic acid, benzenesulfonic acid (BS), and p-hydroxy BS (HBS) had k values of 0.036, 0.018, and 0.018, respectively, suggesting that the ion-exchange interaction mainly occurred via sulfonate groups. Finally, HI-EKC was demonstrated using 0.05% chitin or chitosan NWs. In both cases using chitin and chitosan NWs, HBS showed much stronger interaction with k > 0.192 compared with BS with k < 0.070. It indicated structural difference between NFs and NWs affected the HI behavior in terms of both the ion-exchange and HILIC modes.

Highly sensitive chiral analysis in capillary electrophoresis with large-volume sample stacking with an electroosmotic flow pump

“…The maintained effective separation length was theoretically calculated to be more than 99.8% (see Supporting Information). As with the previous report [22],…”

“…A fused silica capillary was coated with PVA in the same way as the previous papers [22,25,26]. Briefly, the capillary was activated and washed with 1 M NaOH and water, followed by the injection of a 5% PVA solution into the whole capillary.…”

“…In LVSEP-CDCZE, on the other hand, 1/t M is not proportional to v s because t M includes the time of the LVSEP concentration process. Since the time of the LVSEP concentration can be estimated from t i [22], t M was corrected by subtracting with t i in this study for the EE quantification. As a result, EE was estimated as 99.05% ± 0.048% (n = 4) in LVSEP-CDCZE and 99.11% ± 0.082% (n = 4) in conventional CDCZE, indicating that good chiral quantification performance of CDCZE was maintained even after applying LVSEP.…”

“…Moreover, highly efficient preconcentration techniques often require multi-step procedures [16,20], which are quite bothersome and often cause the reduction in the analytical reproducibility. Hence, we focused on an online sample preconcentration technique using field amplified sample stacking, large-volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) [21][22][23], which provides the high sensitivity with almost no loss of resolution in a simple experimental procedure. In our previous work [22], up to 780-fold sensitivity increases were achieved with good separation performance in the CE analysis of oligosaccharides.…”

“…Hence, we focused on an online sample preconcentration technique using field amplified sample stacking, large-volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) [21][22][23], which provides the high sensitivity with almost no loss of resolution in a simple experimental procedure. In our previous work [22], up to 780-fold sensitivity increases were achieved with good separation performance in the CE analysis of oligosaccharides. Moreover, we did not need to optimize the sample injection volume, because the sample filled in the whole capillary could be concentrated.…”