Micellar extraction with vesicle coated multi-walled carbon nanotubes to assist the dispersive micro-solid-phase extraction of natural phenols in Dendrobium

https://doi.org/10.1016/j.jpba.2020.113461Get rights and content

Highlights

  • The catanionic surfactant vesicles were used to disaggregate carbon nanotube bundles.

  • Micellar extraction was employed for the sample pre-extraction.

  • The relative parameters were optimized using response surface methodology.

Abstract

Here, catanionic surfactant vesicles were prepared by varying the types and compositions of anions and cations and the number of alkyl tails of the surfactants. The formed vesicles were employed to disaggregate and stabilize multiwalled carbon nanotubes bundles in aqueous solutions. Furthermore, the vesicle coated carbon nanotubes were used as the adsorbent in the dispersive micro-solid phase extraction. Additionally, micellar extraction was employed for the sample pre-extraction to avoid the use of toxic organic extraction solvents. The relative parameters that affect the extraction efficiency of targets were optimized using response surface methodology. Under the optimal microextraction conditions, the analytical performance of the established method was evaluated. The limits of detection (2.3−13 ng/mL) and quantification (7.6−42 ng/mL), inter- and intra- day precision (1.2–4.0 %, 2.0–5.0 %), and spiked recovery values (80–91 %) were obtained. The proposed method showed high sensitivity, precision and trueness. It was successfully applied to analyze phenols in Dendrobium genus samples.

Introduction

Multi walled carbon nanotubes (MWCNTs) are available for extraction as an adsorbent material because they provide large surface areas and sufficient interaction sites [1]. However, hydrophobic MWCNTs tend to be bundled in water due to the strong van der Waals force among the adjacent tubes, which seriously hinders applications. Many efforts are made to homogeneously distribute CNTs including physical (non-covalent) and chemical (covalent) methods [2]. Chemical modification may result in the change in carbon atom hybridization form and performance of the tubes. Thus, non-covalent modification is commonly used, which have no additional effect on the original structure of MWCNTs. Commonly, π-conjugative compounds [3], surfactants [4] and polymers [5] are employed for noncovalently functionalized MWCNTs. Researchers have focused on dispersing CNTs through single surfactants because of their intrinsic advantages such as low cost, commercial availability and ready use. For example, SDS-coated MWCNTs was successfully synthesized by Valc´arcel et al. [6] and it was used as additive in the liquid–liquid extraction [7]. Although mixed surfactants are superior to individual ones, relative work is still rare for disaggregation and stabilization of MWCNTs by two surfactants.

Vesicle is an organized self-assembly with a bilayer spherical structure. Phospholipid vesicles are extremely uns, which restricts their applications. Cationic/anionic surfactant vesicles have drawn extensive attention because of the spontaneous formation and high stability [8]. The catanionic surfactant vesicle in aqueous solution was first reported by Kaler and his coworkers in 1989 [9]. The unique membrane-enclosed capsule structure makes the vesicle own multiple potential pharmaceutical applications including model cell membrane, drug encapsulation and delivery, protein binders and transfection vectors [10]. To our best knowledge, few works have focused on the dissociation and stabilization of MWCNTs by vesicle.

Dispersive micro-solid phase extraction (D-μ-SPE), as a sample treatment method, exhibited obvious advantages of simplicity and high efficiency [11]. In the D-μ-SPE process, analytes were directly trapped by adsorbing materials and the targeted analytes were desorbed from adsorbents using eluent. Thus, a sui adsorbent plays a critical role in the extraction procedure. Recently, nanoparticles have aroused great interest as effective adsorbents because of their unique size and physicochemical properties [12]. In addition, the surface of nanoparticles can be modified by coating with various materials, which extends their applications [13]. Accordingly, it is meaningful to seek appropriate functionalized nanoparticles.

Plants in the Dendrobium genus are functional foods. There are many different species of Dendrobium, such as D. chrysotoxum Lindl. (D.C.P,), D. nobile Lindl. (D.N.L), and D. officinale (D.O.). The Zhejiang, Yunnan and Anhui provinces are the main habitats of Dendrobium in China. Potential efficacies have been recorded including nourishing yin, clearing heat, improving upset stomach, facilitating body fluid production and improving eyesight. Multiple therapeutic effects may be attributed to various active compounds in Dendrobium, such as polysaccharides, phenanthrenes and bibenzyls. Among them, polysaccharides have been thoroughly studied [14]. However, few works aim to evaluate other active substances, which is bad for the sufficient availability and comprehensive quality evaluation for precious functional food. Phenolic compounds including bibenzyl and phenanthrene are listed as excellent chemical markers for the Dendrobium genus. Among them, gigantol, erianin (bibenzyl compounds), and naringenin (phenanthrene compound) have important pharmacological effects. Considering the complexity of medicinal plants and the importance of active ingredients, it is extremely valuable to explore the optimal extraction method of these compounds.

Here, we confirmed the feasibility of vesicle-coated MWCNTs in the process of d-μ-SPE. The sui parameters were preliminarily optimized by a univariate experiment. Furthermore, the optimal experiment parameters were obtained by response surface methodology (RSM). The green solvent Triton X-100 was used as an extraction solvent. The proposed method was successfully employed to extract phenols in various Dendrobium samples.

Section snippets

Chemicals and reagents

For method development and validation, the anionic surfactants sodium dodecyl sulfate (SDS, Sigma-Aldrich, St Louis, MO, USA, ≥99 %) and sodium octyl sulfate (SOS, Alfa Aesar, 99 %) were used. The cationic surfactants included dodecyltrimethylammonium chloride (DTAC, Aladdin, Shanghai, China, 99 %), dodecyl trimethyl ammonium bromides (DTAB, jkchemical Co., Ltd., Beijing, China), cetyltrimethylammonium bromide (CTAB, Shanghai Lingfeng Chemical Reagent Co., Ltd. Shanghai, China), and

Results of the single-factor experiments

CNTs tend to aggregate in the media of water or organic solvents due to the strong van der Waals interactions between the adjacent tubes, which limits their application as adsorption materials. Here, catanionic surfactant coated vesicles were used to enhance the dispersibility of CNTs. Then, the CNT suspension was applied to enrich three phenols by the D-μ-SPE method. Relevant variables were tested to obtain the optimal extraction conditions.

Conclusion

In this work, a novel d-μ-SPE method was proposed, which was established using vesicle-coated MWCNTs as the adsorbent. The related factors were optimized through the response surface methodology. In this work, the catanionic surfactant vesicle functionalized MWCNTs were employed for the first time as the dispersant in d-μ-SPE to extract phenol compounds from Dendrobium nobile. The vesicle-coated MWCNTs provided a fine dispersant effect and stability. The vesicle preparation was simple and

CRediT authorship contribution statement

Xin Dong: Methodology, Data curation, Writing - original draft, Writing - review & editing. Jun Yang: Conceptualization, Software. Xiao-Ting Zhen: Visualization, Investigation. Yan Chen: Software, Validation. Hui Zheng: Supervision. Jun Cao: Supervision.

Declaration of Competing Interest

The authors declare no competing financial interest.

Acknowledgements

This study was supported by the General Program of public welfare research project of Zhejiang Province (LGF18H280004), National Natural Science Foundation of China (81573552), Hangzhou Social Development of Scientific Research projects (20191203B13), and the Hangzhou 131 middle-aged and young talent training plan (China, 2017).

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