Spherical covalent organic frameworks as advanced adsorbents for preconcentration and separation of phenolic endocrine disruptors, followed by high performance liquid chromatography

Abstract

As a promising generation of porous micro-materials, covalent organic frameworks (COFs) have great potentials for applications in separation and adsorption. In the present study, an advanced food-safety inspection method involving COFs as the adsorbents of solid phase extraction (SPE) is proposed for sensitive and accurate determination of target hazardous substances. Typical spherical TpBD COFs with large surface area and superior chemical stability were utilized as adsorbents for the preconcentration of phenolic endocrine disruptors (PEDs), followed by high performance liquid chromatography (HPLC) analysis. The well-prepared TpBD COFs were encapsulated in SPE cartridges and applied in food research, namely, for the separation and enrichment of four target endocrine disruptors in food samples. The possible factors influencing the SPE performance including the composition of the sample solvent, sample solution pH, sample flow rate, composition of the eluent, and the volume of the eluent were investigated and optimized. Due to the porous architecture and superior surface area of spherical TpBD, the enrichment of analytes via a COF-filled SPE column gave extremely low detection limits of 0.056-0.123 mg L À1 along with a wide linear range of 0.5-100 mg L À1 for all the analytes. Nine parallel determinations of the mixed standard with a concentration of 10 mg L À1 produced the relative standard deviations of 2.23-3.08%, indicating the excellent repeatability of the COF-SPE assay. This study can open up a new route for the employment of COFs as efficient SPE adsorbents for the enrichment and quantification of trace/ultra-trace hazardous materials in complex food samples.

Covalent Organic Frameworks in Sample Preparation

“…Among those shown in Table 1 , there can be found pesticides such as benzoylurea insecticides [ 36 , 37 ] pyrethroids [ 38 ] and carboxylic acid pesticides [ 39 ]. All of them have an endocrine disrupting activity and some of them are potentially carcinogenic and teratogenic, such as certain phenolic and bisphenolic compounds which have also been extracted using COF-SPE [ 40 ]. Moreover, sulphonamides (SAs) [ 41 , 42 ] and inorganic trace ions [ 43 ] have also been determined.…”

“…The types of samples analyzed have been very diverse, as also shown in Table 1 . They include fruits [ 37 , 38 ], juices [ 36 , 37 ], vegetables [ 36 , 37 , 38 ], plant extracts used in traditional Chinese medicine [ 38 ], environmental samples and drinking water [ 37 , 39 , 41 , 43 , 45 ], milk [ 40 , 41 , 43 ], carbonated beverages [ 40 ] and meat [ 41 , 42 , 44 ].…”

“…Liquid samples, such as water [ 37 , 39 , 41 , 43 , 45 ] and other beverages [ 40 ], have been directly extracted with COF sorbents after previous filtration (and degasification for the carbonated ones), whereas solid or semi-solid samples have been, in some cases, first extracted using an organic solvent. In the case of a milk sample, for example, a previous deproteinization step with the help of an acidifying agent for protein precipitation and a subsequent centrifugation is required, and a filtration for the following SPE procedure [ 40 , 41 ]. On the other hand, other samples such as meat [ 41 , 42 , 44 ] have been first minced and a certain solvent, such as acetonitrile (ACN), or even an acid, such as trichloroacetic acid, has been added before it was stirred and centrifuged.…”

“…Concerning the pre-treatment of fruit and vegetable samples, it frequently involves their crushing into small pieces, homogenization, centrifugation and filtering of the supernatant [ 36 , 37 , 38 ]. The COFs that have been used for such purposes can be classified into three groups in terms of composition: conventional or as synthesized COFs [ 36 , 37 , 40 , 44 , 45 ], functionalized COFs [ 39 , 43 ] and hybrid COFs, which result from the combination with other materials—for example, MOFs [ 41 ] or polymers [ 38 , 42 ], among others. COFs belonging to the first group (COFs directly used in SPE) are synthesized following a series of stages from their building blocks.…”

Tailoring Covalent Organic Frameworks To Capture Water Contaminants

“…The frameworks explored for this applicationh ave typicallyf eatured either tetragonal or hexagonal pores (Scheme 1). Promising results have been obtained for the captureo f, for example, organic dyes, [31][32][33][34][35] perfluoroalkyl substances, [36] aryl-organophosphorous flame retardants, [37] pesticides, [38][39][40] phenol endocrine disruptors, [41,42] lactic acid, [43] iodine, [44,45] mercury, [46][47][48][49] radionuclides, [50] lanthanides, [51] and oil spills. [52] We found COFs to efficiently adsorb biotoxins from seawater [53] andp harmaceuticalc ontaminants from water, [54] expanding their use to these classes of hazardouscompounds.…”