Preparation and chromatographic evaluation of a polymer-based stationary phase for weak anion-exchange/hydrophilic interaction

doi:10.3724/SP.J.1123.2019.08019

Abstract

Abstract:

a weak cationic exchange/hydrophilic interaction mixed-mode stationary phase (Sil-PolyCOOH) for high performance liquid chromatography was prepared by bonding polyethylene maleic anhydride to the surface of amino silica gel via a nucleophilic substitution reaction, followed by hydrolysis of the residual maleic anhydride. The new stationary phase material was characterized by solid-state¹³C nuclear magnetic resonance analysis and ζ-potential measurements. The chromatographic performance and retention mechanism of this stationary phase were evaluated using nucleosides and nucleic bases as probes. The effects of mobile phase composition, ion strength, and pH on the retention factor were investigated. The results show that the retention mechanism of the stationary phase involves both hydrophilic distribution interaction and multiple forces between the host and guests. The stationary phase also showed good separation performance for saccharides, diquat, and paraquat. These results show that the stationary phase has a good application prospect in the separation of polar compounds.

Key words: hydrophilic interaction chromatography (HILIC), high performance liquid chromatography (HPLC), weak cation exchange, polyethylene maleic anhydride, stationary phase

CLC Number:

O658

LOU Xuhua, ZUO Huiying, WANG Yuan, ZHAO Wenjie. Preparation and chromatographic evaluation of a polymer-based stationary phase for weak anion-exchange/hydrophilic interaction[J]. Chinese Journal of Chromatography, 2020, 38(4): 430-437.

Figures/Tables 11

Fig. 1 Schematic illustration of the synthetic process of weak anion-exchange/hydrophilic interaction stationary phase DMF: N,N-dimethylformamide.

Fig. 2 Solid-state 13C CP/MAS NMR spectra of Sil-PolyCOOH material 13C CP/MAS NMR: 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy; δ: chemical shift.

Fig. 3 ζ-potential of Sil-PolyCOOH material at different pH levels

Fig. 4 Separation of nucleosides and nucleic bases compounds on Sil-polyCOOH column Mobile phase: CH3CN-ammonium acetate (85∶15, v/v, pH 3.26); detection wavelength: 265 nm. Peak Nos.: 1. thymidine; 2. uridine; 3. inosine; 4. adenine; 5. 2-NH2-adenine nucleoside; 6. cytidine; 7. cytosine.

Fig. 5 Influence of water content in the mobile phase on the retention of nucleosides and nucleic bases k: retention factor; CB: water content in the mobile phase.

Table 1 Linear regression coefficients based on retention models (1), (2), and (3)

Solute	Retention model (1)			Retention model (2)			Retention model (3)
Solute	lg k_w	-S	R²	lg k_B	-A_S/n_B	R²	a	b	c	R²
Thymidine	0.109	3.177	0.975	-1.411	0.913	0.839	2.575	0.894	-11.312	0.986
Uridine	0.276	3.389	0.980	-1.346	0.976	0.846	3.003	0.911	-11.873	0.991
Inosine	0.587	3.723	0.965	-1.204	1.082	0.853	3.114	0.679	-11.608	0.964
Adenine	0.539	2.767	0.970	-0.826	0.847	0.973	-1.237	-0.953	-2.109	0.988
2-NH₂-adenine	0.686	3.147	0.980	-0.861	0.957	0.967	-0.646	-0.857	-3.416	0.992
Cytidine	0.870	3.763	0.987	-0.977	1.140	0.965	-0.279	-0.878	-4.740	0.995
Cytosine	0.874	3.215	0.947	-0.718	0.992	0.968	-1.513	-1.357	-1.336	0.972

Fig. 6 Influence of (a) buffer concentration in the mobile phase and (b) pH values on the retention of model compounds

Fig. 7 Van’t Hoff plots for model compounds on Sil-polyCOOH column Mobile phase: CH3CN-ammonium acetate (85∶15, v/v, pH 3.26); detection wavelength: 265 nm. T: thermodynamic temperature.

Table 2 Thermodynamic parameters for seven model compounds on Sil-polyCOOH column

Analyte	ΔH/ (kJ/mol)	ΔS/ (J/(mol·K))	Correlation coefficient
Thymidine	-7.67	-35.25	0.9996
Uridine	-8.05	-32.91	0.9988
Inosine	-7.56	-31.23	0.9987
Adenine	-7.30	-27.82	0.9998
2-NH₂-adenine	-7.96	-27.89	0.9942
Cytidine	-7.74	-25.31	0.9983
Cytosine	-9.03	-28.14	0.9977

Fig. 8 Separation of saccharides on Sil-polyCOOH column Mobile phase: CH3CN/H2O (90∶10, v/v); ELSD (evaporative light scattering detection): gas pressure, 2×105 Pa; tube temperature, 80 ℃; gain, 30.

Fig. 9 Separation of paraquat and diquat on Sil-polyCOOH column Mobile phase conditions: ACN/15 mmol/L CH3COONH4 (75∶25, v/v); detection wavelength: 257 nm.

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