Fluoro-functionalized stationary phases for electrochromatographic separation of organic fluorides

https://doi.org/10.1016/j.chroma.2020.461269Get rights and content

Highlights

  • Fluoro-functionalized stationary phases for capillary electrochromatography

  • Michael addition and polydopamine functionalization for stationary phase preparation

  • The F-column has excellent separation performance for neutral and fluorinated compounds

  • The column has good reproducibility and stability

Abstract

Fluorous affinity means remarkably specific interaction between highly organic fluorides. This work aims to explore the potential of fluoro-functionalized stationary phase for the separation of organic fluorides by means of fluorous-fluorous interaction. Here, by using the Michael addition strategy between 1H,1H,2H,2H-perfluorodecanethiol (PFDT) and polydopamine (PD), a novel fluoro-functionalized stationary phase was synthesized for open-tubular capillary electrochromatography (OT-CEC). The PFDT@PD was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectrometer (XPS). The PFDT@PD@capillary exhibited outstanding separation performance towards neutral compounds (such as alkylbenzenes and chlorobenzenes) and organic fluorides (such as fluorobenzenes and perfluoroalkyl methacrylates etc.) with high resolution and high separation efficiency by hydrophobic interaction and fluorous-fluorous interaction. In addition, the column shows good stability and reproducibility. The relative standard deviations (RSDs) of the retention time for intra-day (n = 5) and inter-day (n = 3) runs and between columns (n = 3) are less than 0.39%, 1.22% and 3.87%, respectively. This novel type of fluoro-functionalized stationary phase represents a great application potential in organic fluorides separation field.

Introduction

Since the 1950s, perfluorinated compounds (PFCs) are widely used in food and industrial products because of their high chemical stability, good thermal resistance [1], [2], [3]. However, due to the unique properties such as bioaccumulation, toxicity and the harm to human and animal [4], [5], PFCs have become global emerging contaminants and attracted much attention to their influence on human health and environment in recent years [6], [7], [8], [9], [10]. Hence, there is an increasing demand for selective and efficient analytical strategies for the separation of organic fluorides. Fluorous affinity is the character that describes the ability of highly fluorinated or perfluorinated chemical moieties to selectively affinity for one another through strong noncovalent fluorine-fluorine (F-F) interaction, in some way like dissolves like principle [11]. Due to the unique F-F interaction, fluorinated materials have attracted much attention as stationary phases for selective separation of fluorinated analytes.

Chromatographic separation techniques have been intensively used in the separation of organic fluorides such as high performance liquid chromatography (HPLC) [12], [13], [14] and capillary electrochromatography (CEC) [15], [16], [17]. CEC which hybrids the high efficiency of capillary electrophoresis (CE) and high selectivity of high performance liquid chromatography (HPLC) [18] has been considered as a powerful analytical technique for the separation of organic fluorides. Packed, monolithic and open-tubular columns are three basic formats of CEC column. To date, only a few fluorinated monolithic columns have been reported as stationary phases for CEC [15], [16], [17]. Yurtsever et al. [15] firstly prepared a fluorinated monolithic column by the copolymerization of 2,2,2-trifluoroethyl methacrylate (TFEM) with ethylene dimethacrylate (EDMA), and the fluorinated monolith showed good separation perfprmance towards alkylbenzenes, phenols, aniline and benzoic acid derivatives in CEC mode. Choodum et al. [16] synthesized a fluorinated cationic monolith by using thermal initiation copolymerization of perfluorododecyl acrylate (PFDA) and ethylene dimethacrylate (EDMA), the separation performance of the prepared fluorinated monolith was evaluated by phenolic compounds, aromatic hydrocarbons and fluorine-containing compounds. However, the above polymer-based monoliths possess ordinary column efficiency, poor mechanical stability and permeability, which limit their applications. Compared with monolithic column, open-tubular column has the advantages such as absence of bubble and frit formation, ease of preparation, high separation efficiency, good permeability and mechanical stability [19], [20]. These features make OT-CEC a potential new approach for the separation of organic fluorides. As far as we know, there is no report about the OT-CEC separation of organic fluorides. The key of the separation of fluorinated analytes in OT-CEC is the fluorinated stationary phases that can exhibit outstanding separation and recognition abilities based on fluorine-fluorine interaction.

Inspired by the unique covalent and noncovalent interactions ability of polydopamine (PD), applying polydopamine as supporting linker for the immobilization of various materials was reported in recent years [21], [22], [23], [24], [25], [26], [27], [28], [29]. In this work, we reported an approach to prepare a fluorinated stationary phase for OT-CEC by polydopamine functionalization. The PD was rich in amino and catechol groups, provideing an active surface for secondary Michael addition reaction of the thiol group of 1H,1H,2H,2H-perfluorodecanethiol (PFDT) [30], [31], [32], [33], [34], [35]. The resulted column was applied for the separation of various neutral compounds (such as alkylbenzenes and chlorobenzenes) and organic fluorides (such as fluorobenzenes and perfluoroalkyl methacrylates etc.), and baseline separation with high efficiency was obtained. In addition, the PFDT@PD modified column showed outstanding stability and reproducibility. To the best of our knowledge, it is the first time to utilize OT-CEC for separation of fluorinated analytes. This approach would represent a promising approach to separate organic fluorides.

Section snippets

Chemicals and materials

Dopamine hydrochloride and 1H,1H,2H,2H-perfluorodecanethiol (PFDT) were obtained from Sigma-Aldrich (MO, USA). Methylbenzene, ethylbenzene, n-propylbenzene, n-butylbenzene, methylparaben, ethylparaben, propylparaben, chlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, fluorobenzene, 1,2,4-trifluorobenzene, 1,2,4,5-tetrafluorobenzene, pentafluorobenzene, 1H,1H,7H-dodecafluoroheptyl methacrylate (DFHMA), 1H,1H-heptafluorobutyl methacrylate (HFBMA), 1H,1H,2H,2H-nonafluorohexyl methacrylate

Characterization of the PFDT modified open-tubular column

The surface morphology of bare capillary, PD@capillary and PFDT@PD@capillary were characterized using scanning electron microscopy (SEM), As shown in Fig. 2a-b, the inner surface of the bare capillary is very smooth. In Fig. 2c-d, the polydopamine particles were too small, the layer of polydopamine was too thin and not obvious to observed under this SEM magnification (20000 × or 10000 ×). After reaction between the PFDT and PD, the inner surface became much rougher and a large number of

Conclusion

In summary, we have successfully developed a novel hydrophobic and fluorophilicity organic monomer (PFDT) covalent immobilized stationary phase for OT-CEC separation. A series of characterization of the PFDT modified open-tubular column were implemented, such as SEM, FT-IR and XPS. The results illustrate that PFDT is immobilized successfully on the PD layers. The separation capacity of PFDT@PD@capillary was evaluated by separation of various neutral compounds (such as alkylbenzenes and

Credit author statement

Zhentao Li: Investigation, Conceptualization, Methodology, Paper draft writing, Data analysis and administration. Zhenkun Mao: Conceptualization, Methodology, Validation. Changjun Hu: Validation. Qiaoyan Li: Validation. Zilin Chen: Supervision, Funding acquisition, Project administration, Conceptualization, Manuscript revising.

Declaration of Competing Interest

Authors declare no conflict of interest

Acknowledgement

This work was supported by the National Natural Science Foundation of China (Grant Nos. 81872828 and 81573384).

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