br Introduction A pretreatment technique named porous membra

Introduction A pretreatment technique named porous membrane protected micro-solid-phase extraction (μ-SPE) was proposed by Basheer et al. in 2006 [1]. It is based on the packing of small amount of sorbent material in a sealed porous membrane envelope. Compared to other pretreatment techniques, the method has several advantages, such as preventing the loss and blockage of sorbents, reducing matrix effect, portable, durable, robust, easy to manipulate, time and cost saving, and so on. So far, μ-SPE has been widely used as extraction technique for analysis of numerous target compounds in environmental, food, and biological samples [2]. For membrane protected μ-SPE, the choice of sorbent is crucial because it determines the extraction efficiency. Up to now, many porous materials, such as carbon based sorbents [1,[3], [4], [5], [6]], ethylsilane or octadecylsilane modified aldehyde dehydrogenase inhibitor (C2 or C18) [7,8], polymeric materials [[9], [10], [11]], mesoporous silica [12], zeolites [13], and metal organic frameworks (MOFs) [[14], [15], [16]], have been selected as the sorbents of μ-SPE. Among these materials, MOFs materials have shown an exponential growth of interest owe to their microporosity, remarkably low density, extremely large surface area, easily designed or modified to have different pore sizes. However, only MIL-101 [14,15] and ZIF-8 [17,26] have been used as sorbents of μ-SPE for aqueous matrices. One of the main reasons is due to the fact that water molecule could easily penetrate the pores of MOFs and perennially disrupt their framework [18,19]. UiO-66(Zr) (UiO for University of Oslo), first synthesis by Cavka et al. [20], is based on a Zr6O4(OH)4 octahedron, forming lattices by 12-fold connection through the terephthalate linkers, resulting in a cubic close-packed structure [20]. The high degree of topological connectivity together with the strong coordination bonds between zirconium and oxygen renders UiO-66(Zr) to be greatly hydro-stable, even under acidic or some alkaline conditions [21] and performs a high hydrothermal stability up to 450 °C. This provides a theoretical basis of applying UiO-66(Zr) in μ-SPE. UiO-66(Zr) has been used for solid-phase micro-extraction of phenols in water samples [22], magnetic solid-phase extraction of domoic acid from shellfish samples [23], and adsorptive removal of acid [24] and dyes [25] from water, but no reports of UiO-66 used for membrane protected μ-SPE. Natural and synthetic steroid hormones are recognized for their potential to mimic or interfere with normal hormonal functions (development, growth and reproduction) even at ultratrace levels (ng/L) [26]. They are used extensively in clinical and animal husbandry for the prevention and treatment of diseases. Since they cannot be completely metabolized in the body, such substances are excreted in the urine and eventually enter aquatic environments. Steroid hormones are potential risk for wildlife and humans through the consumption of contaminated food or water [27]. Based on structural differences and affinities, steroid hormones can be divided into five subclasses: estrogens, androgens, progestogens, mineral corticoids and glucocorticoids. With lots of work focusing on estrogens, less attention has put on progestogens and androgens. However, these hormonal systems still play an important role on the maintenance of sexual development, growth, and homeostasis, thus there is still a need for sensitive methods to detect these less studied endpoints in environmental water [28].