Self-assembly of core-shell structured multiwalled nanotubes@covalent organic frameworks composite for solid-phase extraction of four phytohormones from fruit juices.

Covalent organic frameworks (COFs) have attracted considerable attention in sample pretreatment because of their unique characteristics. However, the submicron or micron size of COFs has restricted their wider applications in solid-phase extraction (SPE). Herein, multiwalled nanotubes (MWNTs) were used as substrate materials to synthesize core-shell structured MWNTs@COFs composites (MWNTs@SNW-1) using a simple self-assembly method. The as-prepared MWNTs@SNW-1 composite exhibited a high BET surface area, good thermal stability, and good adsorption capacity. The MWNTs@SNW-1 composite was used as an adsorbent in cartridge-based SPE to extract four phytohormones before determining their levels by high-performance liquid chromatography. The experimental parameters affecting extraction efficiency, including the amount of adsorbents, solution pH, ionic strength, eluent type, and eluent volume, were investigated. The developed method showed a wide linear range (0.37-100 ng mL-1), low detection limits (0.11-0.32 ng mL-1), low limits of quantification (0.37-1.07 ng mL-1), high enrichment factors (45.9-49.3), and good reproducibility (<4.8%) for phytohormones. The developed analytical method was used to analyze trace phytohormones in fruit juices with good recoveries, highlighting the potential of the MWNTs@SNW-1 composite as an adsorbent in sample preparation.

Electrospinning fabrication of covalent organic framework composite nanofibers for pipette tip solid phase extraction of tetracycline antibiotics in grass carp and duck.

In the current study, a novel covalent organic frameworks COF-SCU1 incorporated electrospun nanofibers (PAN@COF-SCU1 nanofibers) was fabricated via a facile electrospinning method and utilized as adsorbent in pipette tip solid-phase extraction (PT-SPE) of tetracycline antibiotics (TCs) from foods. The prepared PAN@COF-SCU1 nanofibers possessed both of the unique characteristics of electrospun nanofibers and COFS-CU1, and thus improving the adsorption capacity of the electrospun nanofibers and preventing the problems of leakage and high pressure caused by directly using the nanosize COFs as adsorbent in PT-SPE. The experiments affected the adsorption and desorption efficiencies, such as the loading ratios of COFS-CU1 in nanofibers, the amount of nanofibers, the matrix pH and desorption solvent, were studied in detail. Eventually, a new pipette tip solid-phase extraction-high performance liquid chromatography (PT-SPE/HPLC) method was proposed for the analysis of three TCs from food. Satisfied linearity for TCs was obtained in the range of 4-70 ng mL-1. The limits of detection and quantification were ranged from 0.6 to 3 ng mL-1 and from 2 to 10 ng mL-1, respectively. The interday and intraday precisions (RSD) were all lower than 9%. The proposed PT-SPE/HPLC method was used to determine TCs residues in grass carp and duck samples for the first time. The results could not only explore the availability of PT-SPE in the extraction of TCs in food samples, but also broadened the potential applications of COFs in sample preparation.

Facile synthesis of covalent organic framework incorporated electrospun nanofiber and application to pipette tip solid phase extraction of sulfonamides in meat samples.

In this work, covalent organic frameworks SNW-1 incorporated polyacrylonitrile (SNW-1@PAN) nanofiber was synthesized and used as pipette tip solid phase extraction (PT-SPE) adsorbent for preconcentration of five sulfonamides (SAs) in meat samples. The SNW-1@PAN nanofiber was fabricated via two steps, including the hydrothermal synthesis of SNW-1 and co-electrospinning of the SNW-1/PAN mixture. The three dimensional networks of electrospun nanofiber provide both low backpressure and rapid mass transfer in PT-SPE application, thus preventing the problems of high backpressure and leakage caused by directly packing SNW-1 into PT-SPE cartridge. The SNW-1@PAN nanofiber packed PT-SPE cartridge was used to extract SAs in meat samples followed by high performance liquid chromatography (HPLC). The effects of different parameters influencing the extraction and desorption efficiency were intensively investigated and optimized. Under the optimum conditions, the linear ranges of SAs were in the range of 5-125 ng mL-1 with correlation coefficients above 0.998, and the limits of detection of the five SAs ranged from 1.7 to 2.7 ng mL-1. The interday and intraday precision (RSD) for five replicate extractions of the five SAs (50 ng mL-1 for each) was in the range of 5.4-9.2%. The applicability of the proposed method was examined by analyzing the SAs in the pork and chicken samples. The recoveries of the five SAs varied in the range of 86-111% with good precision, showing the good capability of the proposed method for the determination of SAs in the complicated real samples.