Phthalates (PAEs) have been extensively and increasingly used as plasticizers in plastic products to improve the flexibility, elasticity and durabilit [1]. According to the recent reports, PAEs was accounted for about 70% of the world total plasticisers dosage [2]. However, PAEs are generally physically bound to the polymeric chains and can be released into the surrounding environment [3], [4], [5], where they can persist for months or longer as persistent pollutants [4]. Unfortunately, the studies have proved that some PAEs have carcinogenic, mutagenic, teratogenic and endocrine disrupting effects on animals and human [3,5], and these adverse effects can be passed on to offspring through germline inheritance [6]. Due to the widespread presence and outstanding health risks, several PAEs are classified as priority pollutants by the US Environmental Protection Agency (EPA) [7]. To sensitive detection the content of PAEs in the environment can identify and avoid the risks before they cause harm. Therefore, the development of accurate and sensitive analytical method to detect PAEs is an important issue for monitoring the food safety.

Due to the complexity of the matrix, pre-treatment is required before detecting the content of PAEs in environmental samples. At present, the widely used technologies include solid-phase microextraction (SPME), solid-phase extraction (SPE), magnetic solid-phase extraction (MSPE), and so on [8]. Among them, SPME technology is favored due to its integration of extraction, injection, and concentration, greatly reducing sample pre-treatment time [9]. Due to the volatile nature of PAEs, the pre-treatment way of SPME can greatly reduce experimental time through thermal desorption [10]. It is well-established that the properties of coating materials determine the extraction ability of fibers and the sensitivity of established method. Metal-organic frameworks (MOFs) are the good adsorption material and are constructed through coordination bonds by inorganic metal ion/cluster and organic linker [11], [12], [13]. The metal ion acting (node/center) and the organic linker (bridge) can form the complex net, in which contains massive cavities and channels [14]. Benefited from the crystalline nature, permanent porosity, large specific surface area, structural diversity and easy functionalization, MOFs are widely applied in separation and extraction [15], gas storage [16,17], catalysis [18,19], proton conduction [20,21], luminescence [22], sensing [23], electron conduction [24], energy conversion [25], biomedical applications [26] and other fields. As a used frequently material, increasing the stability of MOF in harsh environments and further improving its performance has always been the pursuit.

At present, some feasible methods have been proposed to accomplish the above goals, including doping with other substances (for example, graphene [27], carbon nanotubes [28], polydimethylsiloxane (PDMS) [29], metal oxides [30], graphitic carbon nitride (g-C3N4) [31], covalent organic frameworks (COFs) [32], etc.) and post-synthesis modification [33]. Thanks to MOF materials are suitable for introducing various functional sites on the framework or in the cavity and the channel, the interaction between host and visitor can be highly controlled in a collaborative and remote manner [14]. To take full advantage of this feature, recently, another relatively novel method for increasing the stability and enrichment performance of MOFs is to introduce hydrophobic ILs into the framework, channel or cavity of MOFs (called IL-induced strategy) [34]. ILs are composed by different organic cations and inorganic/organic anions with the advantages of high thermal stability and adjustable functionality [35]. ILs-based composites showed good extract ability for various organic compounds or metal ions [36], and good selectivity for environmental pollutants [36]. The first study on the performance change after the combination of IL and MOF was applied for CO2/N2 separation, proving that the IL/IRMOF-1 composite possessed enhanced selectivity than parent MOF [37]. Thence, MIL-101, another classic MOF material, was chosen for introduction the BrÖnsted acidic ionic liquid (BAIL) into its nanocages to evaluate the catalytic performance. Owing to the combination of the advantages of IL and the ideal microenvironment of MOF, the obtained composite demonstrated higher catalytic performance than its homogeneous counterpart [38]. Later, a room temperature IL with high CO2 solubility was introduced in ZIF-8 cages to enhanced mechanical properties of MOF-polymer. Presumably accounting in the synergetic force between the IL and MOF, the results showed the mechanical, gas separation and the molecular sieving properties were enhanced, the decomposition temperature of composite was improved [39]. Inspired by this, taking into account the increased selectivity, thermal decomposition temperature and good nano-confined zone effect are all beneficial to the extraction performance for targets, we guessed whether the composite material made by introducing IL into MOF nanocage could be applied to sample preparation for improving the enrichment performance of parent MOF. But as far as we know, this method has not been developed in the sample preparation field.

In this paper, for the first time, the IL-induced strategy was used for introducing hydrophobic IL into the UiO-66-NH2 nanocage to prepare a solid-phase microextraction (SPME) coating, and then to study its effect on improving the enrichment performance of parent MOF sample by the gas chromatography-mass spectrometry (GC–MS) measurements. Firstly, UiO-66-NH2 coating was covalently bonded to hydroxyl functionalized stainless steel fiber. Then, the UiO-66-NH2-coated fiber was put in IL solution for preparing IL/UiO-66-NH2 coating by IL-induced strategy. In IL/UiO-66-NH2 coating, IL was limited within the MOF framework and could interact with PAEs entering MOF holes. The obtained IL/UiO-66-NH2-coated fiber was used to separate and enrich eight PAEs, and the manner of IL in improving extraction performance of IL/UiO-66-NH2 composite was studied. Finally, the prepared IL/UiO-66-NH2-coated fiber was successfully used for detecting trace PAEs in real samples.