1-Butyl-3-aminopropyl imidazolium—functionalized graphene oxide as a nanoadsorbent for the simultaneous extraction of steroids and β-blockers via dispersive solid–phase microextraction

Highlights

• A graphene oxide is chemically functionalized with the ionic liquid 1-butyl-3-aminopropyl imidazolium chloride.

• The resulting nanoadsorbent is employed for the dispersive solid–phase microextraction of steroids and β-blockers.

• A comparison with other graphene-based materials is made.

• The applicability of the procedure is evaluated with real-life matrices

Abstract

In this study, we describe the synthesis of graphene oxide functionalized with the ionic liquid 1-butyl-3-aminopropyl imidazolium chloride and its use as an adsorbent for the dispersive solid–phase microextraction (micro SPE) of four anabolic steroids and six β-blockers from aqueous samples of environmental importance, prior to their HPLC-diode array detector analysis. As the ionic liquid is covalently attached to graphene oxide sheets, it is made possible for it to participate in the dispersive micro SPE procedure. The limits of detection and limits of quantification of the proposed method were found to be in the range of 7–23 ng/L and between 20 and 70 ng/L, respectively. The linearity was satisfactory, with the determination coefficients to range from 0.9940 to 0.9998 while the within- and between-day relative standard deviation of the method ranged between 3.1 and 7.6% and from 4.0 to 8.5%, respectively. In order to test the applicability of the proposed method in real-life samples, the effluent from a municipal wastewater treatment plant as well as natural water samples from two rivers and a lake were collected and analyzed. After the analysis of samples, the effluent from municipal wastewater treatment plant was fortified with the analytes, at concentrations equal to 2 and 10 times the LOQs. Recoveries were calculated after subtracting the native (no-spike) concentrations of analytes, when needed. All the recoveries were in the range of 87–98%. A comparison study attests to the superiority of the developed nanomaterial over graphene oxide and graphene for the dispersive micro SPE of steroids and β-blockers.

Introduction

Among the emerging contaminants, pharmaceuticals and endocrine disrupting compounds are of particular concern due to their ubiquity in the aquatic environment and their effects on humans and marine organisms [1], [2], [3]. Out of the compounds reported, emphasis is placed on β-blockers (known also as β-adrenergic antagonists) due to their intensive use for the treatment of various cardiovascular disorders, poor degradability and inefficient removal by wastewater treatment processes [4], [5]. Likewise, among the endocrine disrupting compounds reported, steroids have been suggested as major contributors to the endocrine disrupting activity [6]. Both categories of chemical compounds are able to affect the balance of ecological systems, even at low concentrations. It is easy, therefore, to understand the necessity for their determination in the environment. Hitherto, various extraction techniques, such as membrane extraction [7], solid–phase extraction [8], [9], solid–phase microextraction [10], [11], [12], [13], liquid–phase microextraction [4], [7], [10], [14], [15], [16] were used to extract these classes of compounds from aqueous matrices. All these techniques possess pros and cons making each one more preferable than the others, under different circumstances.

Dispersive liquid–liquid microextraction is an alternative to the classical liquid–liquid extraction and includes extractant volumes, at microliter levels [17]. Briefly, a mixture of an extracting and a dispersing solvent is rapidly injected in an aqueous sample and a cloudy solution is formed. In this way, the contact area between the sample and the extractant is maximized, the extraction time is limited and the efficiency increases [18]. Phases can be separated after extraction by centrifugation. Alternatively, a solid phase can be dispersed in an aqueous sample and therefore, the interactions between the two phases are maximized resulting in a dispersive solid–phase microextraction mode (micro SPE). The analytical instruments used to carry out the separation and the analyses of the two classes of compounds are mainly gas and liquid chromatography coupled to mass spectrometric detector.

Nanomaterials have sparked intense research interest in analytical chemistry because of their known appealing properties [19], [20]. The application of nanomaterials in extraction procedures, as stationary phases or adsorbents, has undergone rapid growth, in recent years [21], [22]. Various analytical procedures based on nanomaterials as extracting phases have been published, signifying their tremendous potential and usefulness. Graphene and its precursor graphene oxide (GO) are nano-scale materials with outstanding properties. Owning to miscellaneous chemical functional groups, such as epoxy, hydroxyl and carboxyl, GO can conveniently be modified, chemically, to enhance the extraction yield and selectivity for specific analytes [23], [24]. So far, modifications of the GO layers, including functionalization with aminosilica and zero-valent iron particles [25], [26] have been proposed.

Ionic liquids (ILs) are organic salts, composed of cations and anions that do not crystalize at room temperature [27]. Due to their intriguing properties, such as tunable viscosity and miscibility, as well as high solvation interactions, with both polar and non-polar compounds, they have been utilized in chemical analysis [28], [29], [30], [31], [32]. They have been used mostly under the extraction principles of single-drop microextraction and dispersive liquid–liquid microextraction [30] since they can increase the extraction efficiency of these techniques, for various classes of analytes. Lately, GO was also functionalized with ILs for various applications such as capacitors and supercapacitors, electrochemical analysis, microextraction sorbents and various biosensors [33], [34], [35], [36], [37], [38]. Combining the two above mentioned major fields, i.e., nanomaterials and ILs, it is made possible to design and develop new extracting materials with outstanding properties. The novel GO materials, modified with ILs, are expected to possess the advantages of both components of the functionalized material, resulting in new, advanced adsorbents with tunable extraction capabilities.

In this study, we describe the synthesis of GO, functionalized with 1-butyl-3-aminopropyl imidazolium chloride, as IL and its use as an extracting phase for the dispersive micro SPE of four anabolic steroids and six β-blockers (Table 1), considered to be micropollutants in the aquatic environment, prior to their HPLC–diode array detector (DAD) analysis. Since the IL is covalently bonded on GO sheets, it is made possible for it to participate in the dispersive micro SPE procedure. The study highlights the superiority of the developed nanomaterial over pristine GO and graphene for the dispersive micro SPE of steroids and β-blockers. To the best of our knowledge, this is the first time that such a composite materials is employed in a microextraction procedure.