Elsevier

Talanta

Volume 169, 1 July 2017, Pages 227-238
Talanta

A novel metal-organic framework composite MIL-101(Cr)@GO as an efficient sorbent in dispersive micro-solid phase extraction coupling with UHPLC-MS/MS for the determination of sulfonamides in milk samples

https://doi.org/10.1016/j.talanta.2016.08.086Get rights and content

Highlights

  • MIL-101(Cr)@GO-based material was firstly applied in the analysis of SAs in milk.

  • MIL-101(Cr)@GO was firstly used as sorbent in a DMSPE procedure.

  • The DMSPE based on MIL-101(Cr)@GO towards SAs was systematically optimized.

  • The proposed method exhibited excellent extraction property for SAs in milk samples.

Abstract

As a novel material, metal-organic framework/graphite oxide (MIL-101(Cr)@GO) has great potential for the pretreatment of trace analytes. In the present study, MIL-101(Cr)@GO was synthesized using a solvothermal synthesis method at the nanoscale and was applied as sorbent in the dispersive micro-solid phase extraction (DMSPE) for the enrichment of the trace sulfonamides (SAs) from milk samples for the first time. Several experimental parameters including kinds of sorbents, the effect of pH, the amount of MIL-101(Cr)@GO, ionic strength, adsorption time, desorption solvent and desorption time were investigated. Under the optimal conditions, the linear ranges were from 0.1 to 10 μg/L, 0.2–20 μg/L or 0.5–50 μg/L for the analytes with regression coefficients (r) from 0.9942 to 0.9999. The limits of detection were between 0.012 and 0.145 μg/L. The recoveries ranged from 79.83% to 103.8% with relative standard deviations (RSDs)<10% (n=3). MIL-101(Cr)@GO exhibited remarkable advantages compared to MIL-101(Cr), MIL-100(Fe), activated carbon and other sorbent materials used in pretreatment methods. A simple, rapid, sensitive, inexpensive and less solvent consuming method of DMSPE-ultra-high performance liquid chromatography-tandem mass spectrometry (DMSPE-UHPLC-MS/MS) was successfully applied to the pre-concentration and determination of twelve SAs in milk samples.

Introduction

Sulfonamides (SAs), an important class of antibacterial compounds, are widely used in veterinary practice to promote the growth of livestock and to prevent and treat the bacterial infections with lower cost [1], [2]. However, the abuse and the unnecessary administration of SAs may result in the accumulation of chemical residues in cattle and then induce adverse effects on human beings by such veterinary products, such as hypersensitive allergic reactions, drug-resistant problems and even carcinogenic character [3], [4]. Milk is a kind of nutritious wholesome food consumed globally since it is an inexpensive source of protein and calcium essential for promoting growth in human health. Therefore, the presence of SAs residues in milk is of great public concern. Accordingly, it is desirable to determine the contents of SAs in milk samples for milk safety and human health protection.

Sample pretreatment for both cleaning up samples and pre-concentrating prior to instrumental analysis is a crucial step in the whole analytical process, especially in the analysis of trace materials in complex matrices. In recent years, some typical methods have been applied in milk sample matrix, such as solid-phase extraction (SPE) [5], solid-phase micro-extraction (SPME) [6], dispersive solid phase extraction (DSPE) [7], matrix solid-phase dispersion (MSPD) [8], and so on. Although each of these methods has its advantages, shortcomings still exist in these procedures. For example, the MSPD is a simple and efficient pretreatment method, but time-consuming purification processes are usually required when it is used to pretreat high-fat samples. SPME performs with high enrichment ability and low organic solvent consumption, but it suffers from low recovery and reproducibility. Generally, SPE is one of the most widely used sample pretreatment techniques. However, it is time-consuming, expensive and more toxic organic solvent consuming in the conventional mode. In 2003, Anastassiades and coworkers introduced a novel sample pretreatment technique named dispersive solid phase extraction (DSPE) to simplify the SPE process [9]. In 2009, dispersive micro-solid phase extraction (DMSPE) was reported by Tsai and his coworker as alternative miniaturization model of DSPE or SPE [10].

The whole DMSPE process only needs a smaller quantity of organic solvent and sorbent. It allows the analytes in aqueous sample to interact equally with all the sorbent particles to achieve greater capacity per mass of sorbent used. Moreover, This method avoids the channeling or blocking that easily occurs in the conventional SPE column or disks [11]. Based on all mentioned above, DMSPE technique has been successfully applied to the separation and the pre-concentration of pesticides [12], water contaminants [11], [13] and pharmaceuticals [10], [14] in different types of matrices including water, foods and biological samples by using different sorbents. It is worthy to mention that Yahaya used mesoporous carbon as the sorbent in DMSPE to extract penicillins in milk [15]. And, Iron oxide functionalized graphene oxide was also used as the sorbent in DMSPE to extract SAs in milk samples [16]. To our knowledge, the core of DMSPE is the sorbent materials that would remarkably impact the selectivity and the enrichment efficiency for the targets. Therefore, it is of great significance to prepare an excellent sorbent for the DMSPE technique.

Recently, Metal–organic frameworks (MOFs) have drawn a growing interest in the fields of adsorption and separation due to their ultrahigh porosity, enormous surface areas and tunable poresize [17], [18], [19], [20], [21], [22]. However, poor stability in humid conditions of MOFs restricted their applications in liquid phase. Encouragingly, MIL-101(Cr), reported by Férey [23], is one of the most prominent sorbents among thousands of MOFs owing to its attractive features such as large surface area, numerous unsaturated metal sites, high porosity, excellent chemical stability and inexpensiveness. What's more, if its dispersive forces are enhanced by combining MOF materials with other substrates, the adsorption performance of MOFs would be further improved due to their low density of atoms in the framework structure. In this sense, graphite oxide (GO) would be a great candidate as the hybrid substrates, since it has many epoxy and hydroxyl functional groups in the plane surface of each sheet accompanied by carboxyl groups in the edges [24], [25]. These functional groups not only make it easier to disperse in water and other solvents with long-term stability [26], but also offer possibility to form hydrogen bonding and electrostatic interactions with organic compounds or metal ions. Bandosz group have developed MOFs@GO composites [24], [25], [26], [27] by unifying the favorable properties of carbonaceous graphite surfaces and tunable MOFs apart. It was found that the addition of GO would extremely enhance the adsorption capacity and the stability in water solution of the prepared composite [28]. MIL-101(Cr)@GO has been successfully used to adsorpt azo dyes from water samples [29], nitrogen-containing compounds (NCCs) and sulfur-containing compounds (SCCs) from model fuels [30], a series of linear long chain alkanes from n-pentane to n-octane [31]. According to literature survey, MIL-101(Cr)@GO has not so far been used for the DMSPE of simultaneous or individual sulfonamide compounds. Consequently, MIL-101(Cr)@GO composite would have a potential to be adsorbent material to extract alternative analytes.

Herein, the preparation of MIL-101(Cr)@GO employed a modified simple hydrothermal method, a rapid, simple, and effective dispersive micro-solid-phase extraction (DMSPE) based on the novel MIL-101(Cr)@GO sorbent was developed to extract twelve SAs coupling with UHPLC-MS/MS detection in milk for the first time. The unique advantage of this method as well as the fact that there is no other report about the utilization of MIL-101(Cr)@GO in DMSPE motivated us to investigate its capability for the extraction and separation of sulfonamides. The present work focuses on the synthesis of MIL-101(Cr)@GO as a newly designed material for DMSPE and the optimization of the extraction and the detection conditions. This study would provide a new strategy for the pretreatment of SAs in milk as well as an important insight for the applications of the MOFs@GO composite material for the extraction of other analytes in different matrixes.

Section snippets

Reagents and materials

Chromium nitrate nonahydrate (Cr-(NO3)3·9H2O), trimesic acid (1, 3, 5-BTC), terephthalic acid (H2BDC), and hydrofluoric acid (HF) were purchased from the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Graphite powder was purchased from Shanghai Aladdin Chemistry Co., Ltd. (Shanghai, China). Potassium permanganate (KMnO4), sodium nitrate (NaNO3), and H2O2 (30%) were purchased from Kermel Chemical Reagent Co., Ltd. (Tianjin, China). Concentrated nitric acid (HNO3), concentrated

Characterization results

The prepared GO and MIL-101(Cr)@GO were characterized by means of XRD, SEM, TGA and N2 adsorption–desorption experiment (Fig. 2). As shown in Fig. 2A, the powder XRD pattern of the synthesized MIL-101(Cr)@GO was nearly the same as that of the MIL-101(Cr) previously reported [34]. The XRD patterns implied that the MIL-101(Cr)@GO preserved the crystalline character of the parental MIL-101(Cr). In Fig. 2B, we can see the diffraction peak of GO at about 10´, which implied that the GO was

Conclusion

In this work, a novel MIL-101(Cr)@GO with both larger BET and higher pore volume than parent MIL-101(Cr) was successfully synthesized using the hydrothermal method. Its stability in water and various solvents allowed it to be used in the sample preparation of aqueous samples with good extraction capability for the trace analysis. The proposed dispersive micro-solid phase extraction (DMSPE) technique based on the synthesized composite material was proved to be an efficient strategy for the rapid

Acknowledgments

This work was supported by Liaoning Representative Office of China Environment Protection Foundation (No: CEPF2013-123-2-10).

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