Preparation and characterization of vinyl-functionalized mesoporous organosilica-coated solid-phase microextraction fiber

Abstract

Vinyl-SBA-15 mesoporous organosilica was synthesized and used as coating material of solid-phase microextraction (SPME) by two coating techniques (direct coating and sol–gel). The synthesized vinyl-SBA-15 organosilica had highly ordered mesoporous structure, good thermal stability and a specific surface area of 688 m² g⁻¹. The fibers prepared by two methods were evaluated by the extraction of non-polar compounds (BTEX, benzene, toluene, ethylbenzene, o-xylene) and polar compounds (phenols). The results showed that the vinyl-SBA-15 fibers prepared by two methods exhibited high thermal stability (310 °C for direct-coated and 350 °C for sol–gel) and excellent solvent durability in methanol and acetonitrile. The fibers also presented much better extraction performance for both polar compounds (phenols) and non-polar compounds (BTEX), compared to commercial polydimethylsiloxane (PDMS) fiber, as well as wide linear ranges, low detection limits (0.008–0.047 μg L⁻¹ for BTEX, sol–gel; 0.15–5.7 μg L⁻¹ for phenols, direct-coated), good repeatabilities (RSDs less than 5.4% for BTEX) and satisfying reproducibilities between fibers (RSDs less than 5.8% for BTEX). The self-made fibers were successfully used for the analysis of BTEX and phenols in three aqueous samples including tap water, mineral water and lake water, which demonstrated the applicability of the vinyl-SBA-15 fibers.

Introduction

Since its introduction by Pawliszyn and co-worker in 1990 [1], solid-phase microextraction (SPME) has been widely applied in many fields due to its solventless, sensitive and easy to use [2], [3], [4]. SPME is based on the distribution effect of analytes between the sample and the extraction phase, which is typically immobilized on a fused silica fiber or metal wire. For this reason, the fiber coating plays the most important role in SPME and preparing SPME fibers with new techniques and new materials obtained a lot of concerns [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]. To date, sol–gel technology [6], [7], [8], [9], molecularly imprinted technology [10], [11], [12], [13] and electrochemical/physical deposition methods [14], [15], [16], [17], [18] have been successfully applied in the preparation of SPME fibers. Carbon nano-materials, such as carbon nanotubes (CNTs) [19], [20], [21], graphene [22], [23], [24], and nanoporous carbon [25], [26], metal nanoparticles [16], [27], metal-organic frameworks (MOFs) [28], [29], etc., have been used as coating materials and exhibited good extraction efficiency to different analytes.

The ordered mesostructure silica materials were first prepared by Mobil researchers in 1992 [30]. These kinds of materials have large surface area, highly ordered pore structure, very tight pore size distributions and thus have been considered as attractive candidates for a wide range of applications in catalysis, sensors and separation technologies [31]. Nowadays, more and more organic functionalized mesoporous silica materials have been introduced by two approaches, post-grafting and direct synthesis [32], [33], [34], [35], [36]. In the former method, organic functional groups are covalently attached to the pore surface by the reaction of the existing of high concentration of surface silanol groups. Amino, thiol, cyclodextrin and alkyl groups had been attached onto the mesoporous structure [32], [33], [34], [35], and this method has been identified as a convenient method to obtain highly effective sorbents. Compared to the post-grafting method, the direct synthesis, involving one-step cocondensation of tetraalkoxysilanes and organosilanes, offers a higher and more uniform surface coverage of functional groups and a better control of the surface properties of the resultant materials [36].

In the field of SPME, the application of mesoporous silica as fiber coating material is still scarce. MCM-41 and phenyl functionalized MCM-41 mesoporous organosilica as fiber coating in SPME were reported by Hou et al. [37], [38], better adsorption and selectivity were found. Compared with MCM-41, SBA-15 materials are more desirable because they have better thermostability owing to their more regular structure, larger pore sizes and thicker pore wall [39]. Hashemi et al. synthesized amino-ethyl-functionalized SBA-15 as SPME fiber coating and good extraction ability for phenolic compounds was observed due to the introduction of amino groups [40].

Vinyl groups are hydrophobic and have many applications value in selective adsorption, catalysis and separations [41], [42]. In this work, vinyl-functionalized SBA-15 was prepared by one-step synthesis method, and used as coating material of SPME based on sol–gel and immobilized resin (direct coating) techniques. A series of experiments were performed to evaluate the performance and characterization of the vinyl-SBA-15 coating material.