Hydroxyapatite surface-functionalized monolithic column for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid.

To date, hydroxyapatite (HAP) based monoliths were mainly fabricated by directly doping of HAP, which suffered from less effective coverage of HAP. Herein, a HAP surface-functionalized monolithic column (HAP@PDA@UF) has been prepared by in-situ biomineralization and applied as sorbent for selective in-tube solid phase microextraction of zoleronic acid and risedronic acid. A polydopamine coating was first generated on the surface of the parent urea-formaldehyde resin monolith; and then HAP microcrystals were further grew on the polydopamine coating to achieve this preparation. SEM, EDAX, FTIR, XPS and mercury intrusion method were utilized for the characterization of the HAP@PDA@UF monolith, and provided evidences of this successful preparation. The selective extraction mechanism of the HAP@PDA@UF monolith was investigated by the optimization of methanol percentage in the sampling solution, phosphate concentration in the eluent. Other crucial factors, including sampling and elution flow rate, and collection time span, were also optimized for the desired SPME performance. Under the optimal conditions, the proposed method showed low LODs of 0.1 µg/mL, satisfactory recoveries of 79.6%-92.5% with RSDs less than 2.7%, and good reproducibility with RSD less than 6.9%, which demonstrated the excellent application of the HAP@PDA@UF monolith, and its potential as a promising selective sorbent for bisphosphonates.

Sulfonate-bonded covalent organic polymer as mixed-mode sorbent for on-line solid-phase extraction of ß2-receptor agonists.

A novel sulfonate-bonded covalent organic polymer (COPTPBA-BPDA@SA) with mixed-mode interactions of hydrophobic and cation-exchange was synthesized and exploited as sorbent for on-line solid-phase extraction (on-line SPE) of ß2-receptor agonists. The successful synthesis of COPTPBA-BPDA@SA was confirmed by the characterization of SEM, XPS and FT-IR. Due to the excellent mixed-mode extraction ability towards the positively charged ß2-receptor agonists and the good anti-interference performance, COPTPBA-BPDA@SA was introduced into on-line SPE-HPLC system for selective extraction of ß2-receptor agonists in pork and pork liver. Via the optimization of the extraction condition, including formic acid percentage and ACN percentage in the sampling solution, the mixed-mode extraction mechanism of COPTPBA-BPDA@SA was investigated. The elution condition, such as the pH value, formic acid percentage and ACN percentage of the eluent was also optimized for the desired SPE performance. Under the optimized condition, COPTPBA-BPDA@SA revealed better purification performance than COPTPBA-BPDA without sulfonating. The LODs for ß2-receptor agonists were in the range of 0.08-0.22 µg/kg, and the recoveries in different samples at three spiked levels (0.4, 4.0, 8.0 µg/kg) were ranged from 83.2% to 98.5% with RSDs less than 5.2%, which indicated the satisfactory mixed-mode extraction ability of COPTPBA-BPDA@SA as well as the good applicability of the developed method.

Hydroxyapatite-embedded monolithic column for selective on-line solid-phase extraction of adenosine triphosphate and its phosphorylated metabolites.

A novel hydroxyapatite-embedded monolithic column has been facilely prepared in a stainless-steel column with inner diameter of 2.1 mm by the strong adhesion of urea-formaldehyde (UF) resin and exploited as a sorbent for selective on-line solid-phase extraction (on-line SPE) of adenosine triphosphate and its phosphorylated metabolites. The composition for this preparation, including the amount of hydroxyapatite nanopowders and the porogen were investigated to obtain a suitable monolith with large surface area and satisfactory permeability. Owing to anion exchange interaction of hydroxyapatite and hydrophilic interaction of UF monolithic matrix, the prepared monolith showed good extraction efficiency and selectivity towards these phosphorylated analytes. Several parameters for on-line SPE, including ACN percentage in the sampling solution, collection time span, salt concentration of the eluent, sampling and elution flow rate, were optimized with respect to the extraction efficiencies of the target compounds. Under the optimized conditions, the LODs of the analytes were in the range of 0.01-0.04 µg/g, the recoveries in the spiked samples ranged from 78.3%-92.5% with RSDs <4.7%. Due to the excellent extraction ability towards phosphorylated compounds in practical samples, a simple on-line SPE-HPLC method using hydroxyapatite-embedded monolith as sorbent has been proposed for monitoring freshness of grass carp.

Poly (Octadecyl Methacrylate-Co-Trimethylolpropane Trimethacrylate) Monolithic Column for Hydrophobic in-Tube Solid-Phase Microextraction of Chlorophenoxy Acid Herbicides.

Chlorophenoxy acid herbicides (CAHs), which are widely used on cereal crops, have become an important pollution source in grains. In this work, a highly hydrophobic poly (octadecyl methacrylate-co-trimethylolpropane trimethacrylate) [poly (OMA-co-TRIM)] monolithic column has been specially prepared for hydrophobic in-tube solid-phase microextraction (SPME) of CAHs in rice grains. Due to the hydrophobicity of CAHs in acid conditions, trace CAHs could be efficiently extracted by the prepared monolith with strong hydrophobic interaction. Several factors for online hydrophobic in-tube SPME, including the length of the monolithic column, ACN and trifluoroacetic acid percentage in the sampling solution, elution volume, and elution flow rate, were investigated with respect to the extraction efficiencies of CAHs. Under the optimized conditions, the limits of detection of the four CAHs fell in the range of 0.9-2.1 µg/kg. The calibration curves provided a wide linear range of 5-600 µg/kg and showed good linearity. The recoveries of this method ranged from 87.3% to 111.6%, with relative standard deviations less than 7.3%. Using this novel, highly hydrophobic poly (OMA-co-TRIM) monolith as sorbent, a simple and sensitive online in-tube SPME-HPLC method was proposed for analysis of CAHs residue in practical samples of rice grains.