Sulfated and sulfonated polysaccharide as chiral stationary phases for capillary electrochromatography and capillary electrochromatography–mass spectrometry

Abstract

The applications of polysaccharide phenyl carbamate derivatives as chiral stationary phases (CSPs) for capillary electrochromatography (CEC) are often hindered by longer retention times, especially using a normal-phase (NP) eluent due to very low electroosmotic flow (EOF). Therefore, in this study, we propose an approach for the aforementioned problems by introducing two new types of negatively charged sulfate and sulfonated groups for polysaccharide CSPs. These CSPs were utilized to pack CEC columns for enantioseparation with a NP eluent. Compared to conventional cellulose tris(3,5-dimethylphenyl carbamate) or CDMPC CSPs, the sulfated CDMPC CSP (sulfur content 4.25%, w/w) shortened the analysis time up to 50% but with a significant loss of enantiomeric resolution (~60%). On the other hand, the sulfonated CDMPC CSP (sulfur content 1.76%, w/w) not only provided fast throughput but also maintained excellent resolving power. In addition, its synthesis is much more straightforward than the sulfated one. Furthermore, we studied several stationary phase parameters (CSP loading and silica gel pore size) and mobile phase parameters (including type of mobile phase and its composition) to evaluate the throughput and enantioselectivity. Using the optimized conditions, a chiral pool containing 66 analytes was screened to evaluate the enantioselectivity under three different mobile phase modes (i.e., NP, polar organic phase (POP) and reversed-phase (RP) eluents). Among these mobile phase modes, the RP mode showed the highest success rate, whereas some degree of complementary enantioselectivity was observed with NP and POP. Finally, the feasibility of applying this CSP for CEC–MS enantioseparation using internal tapered column was evaluated with NP, POP and RP eluents. In particular, the NP-CEC–MS provided significantly enhanced sensitivity when methanol was replaced with isopropanol in the sheath liquid. Using aminog-lutethimide as model chiral analyte, all three modes of CEC–MS demonstrated excellent durability as well as excellent reproducibility of retention time and enantioselectivity.

Enantioselective capillary electrochromatography: Recent developments and new trends

“…While an anionexchanger selector is often used for the separation of acidic compounds, two neutral compounds could be separated here, indicating that the ion-pairing interaction is not really needed for enantiorecognition on this CSP. A comparison was also made with silica particles containing the same immobilized selector and it was seen, as in [29], that zirconia-based material had higher retention, but better Rs and enantioselectivity.…”

“…As an alternative to classical cellulose tris (3,5-dimethylphenylcarbamate) selectors, Zheng et al [29] introduced the sulfated and sulfonated versions of this selector to improve the EOF, which is often weak in normal-phase (NP) and reversed-phase (RP) modes (due to the coating of the surface silanols in RP) on the classical polysaccharide selectors. They found that the sulfated cellulose tris(3,5-dimethylphenylcarbamate)-based CSP indeed had an improved EOF, but at the cost of the separation.…”

Chiral Separation on Sulfonated Cellulose Tris(3,5-dimethylphenylcarbamate)-coated Zirconia Monolith by Capillary Electrochromatography

“…The resulting mixture was injected into the activated fused silica capillary up to the required length and allowed to react overnight at 35 o C. Then, the column was heated at 150 o C for 6 h. After completion of heating, the capillaries were cooled to room temperature and then characterized by SEM. CDMPC was prepared as per the reported method 43 and SCDMPC was prepared as per the reported method 42 and characterized by elemental analyses, IR and NMR spectroscopy. To perform the CDMPC and SCDMPC coatings on the surface of ZM bed, the ZM capillaries were initially washed with ethanol and then with THF.…”

“…42 The augmented EOF generated by the negative charges of the sulfonate groups and dissociated zirconol groups of the ZM surface as well will provide much faster separation than native CDMPC. It is expected that the better chiral resolution in the shorter analysis time is obtained on SCDMPC.…”

Advances in synthetic optically active condensation polymers - A review

“…Chiral recognition of optically active polymers has been utilized in various forms of catalytic and separation chemistry. For example, one of the generally function of chiral polymers is the use as chiral stationary phase in high-performance liquid chromatography (HPLC) for the separation of racemic mixtures [2,[34][35][36][37][38]. Optically active polymers were divided to three types: biopolymers, polymers prepared by almost completely isotactic polymerization by modification of naturally occurring polymer backbones such as polysaccharides and synthetic polymers [2].…”