Xingliang Song

Quercetin molecularly imprinted polymers: Preparation, recognition characteristics and properties as sorbent for solid-phase extraction

Molecular imprinted polymers (MIPs) were prepared through thermal polymerization by using quercetin as the template molecule, acrylamide (AA) as the functional monomer and ethylene glycol dimethacrylate (EDMA) as the cross-linker in the porogen of tetrahydrofuran (THF). The synthesized MIPs were identified by both Fourier transform infrared (FTIR) and scanning electron microscope (SEM). Systematic investigations of the influences of key synthetic conditions, including functional monomers, porogens and cross-linkers, on the recognition properties of the MIPs were conducted. Scatchard analysis revealed that the homogeneous binding sites were formed in the polymers. Besides quercetin, two structurally similar compounds of rutin and catechol were employed for molecular recognition specificity tests of MIPs. It was observed that the MIPs exhibited the highest selective rebinding to quercetin. Accordingly, the MIPs were used as a solid-phase extraction (SPE) sorbent for the extraction and enrichment of quercetin in cacumen platycladi samples, followed by HPLC-UV analysis. The application of MIPs with high affinity and excellent stereo-selectivity toward quercetin in SPE might offer a novel method for the enrichment and determination of flavonoid compounds in the natural products.

Dummy molecularly imprinted polymers-capped CdTe quantum dots for the fluorescent sensing of 2,4,6-trinitrotoluene.

Molecularly imprinted polymers (MIPs) with trinitrophenol (TNP) as a dummy template molecule capped with CdTe quantum dots (QDs) were prepared using 3-aminopropyltriethoxy silane (APTES) as the functional monomer and tetraethoxysilane (TEOS) as the cross linker through a seed-growth method via a sol-gel process (i.e., DMIP@QDs) for the sensing of 2,4,6-trinitrotoluene (TNT) on the basis of electron-transfer-induced fluorescence quenching. With the presence and increase of TNT in sample solutions, a Meisenheimer complex was formed between TNT and the primary amino groups on the surface of the QDs. The energy of the QDs was transferred to the complex, resulting in the quenching of the QDs and thus decreasing the fluorescence intensity, which allowed the TNT to be sensed optically. DMIP@QDs generated a significantly reduced fluorescent intensity within less than 10 min upon binding TNT. The fluorescence-quenching fractions of the sensor presented a satisfactory linearity with TNT concentrations in the range of 0.8-30 μM, and its limit of detection could reach 0.28 μM. The sensor exhibited distinguished selectivity and a high binding affinity to TNT over its possibly competing molecules of 2,4-dinitrophenol (DNP), 4-nitrophenol (4-NP), phenol, and dinitrotoluene (DNT) because there are more nitro groups in TNT and therefore a stronger electron-withdrawing ability and because it has a high similarity in shape and volume to TNP. The sensor was successfully applied to determine the amount of TNT in soil samples, and the average recoveries of TNT at three spiking levels ranged from 90.3 to 97.8% with relative standard deviations below 5.12%. The results provided an effective way to develop sensors for the rapid recognition and determination of hazardous materials from complex matrices.

Determination of 16 polycyclic aromatic hydrocarbons in seawater using molecularly imprinted solid-phase extraction coupled with gas chromatography-mass spectrometry

A method of solid-phase extraction (SPE) using molecularly imprinted polymers (MIPs) as adsorbent coupled with gas chromatography-mass spectrometry (GC-MS) was developed for the determination of 16 types of polycyclic aromatic hydrocarbons (PAHs) in seawater samples. The MIPs were prepared through non-covalent polymerization by using the 16 PAHs mixture as a template based on sol-gel surface imprinting. Compared with the non-imprinted polymers (NIPs), the MIPs exhibited excellent affinity towards 16 PAHs with binding capacity of 111.0-195.0 μg g(-1), and imprinting factor of 1.50-3.12. The significant binding specificity towards PAHs even in the presence of environmental parameters such as dissolved organic matter and various metal ions, suggested that this new imprinting material was capable of removing 93.2% PAHs in natural seawater. High sensitivity was attained, with the low limits of detection for 16 PAHs in natural seawater ranging from 5.2-12.6 ng L(-1). The application of MIPs with high affinity and excellent stereo-selectivity toward PAHs in SPE might offer a more attractive alternative to conventional sorbents for extraction and abatement of PAH-contaminated seawater.

One-pot synthesis of magnetic molecularly imprinted microspheres by RAFT precipitation polymerization for the fast and selective removal of 17β-estradiol

A facile strategy was developed to prepare magnetic molecularly imprinted microspheres (MMIMs) for the selective recognition and effective removal of 17-beta-estradiol (17β-E2) by reversible addition-fragmentation chain transfer precipitation polymerization. One-pot synthesis was employed, which could simplify the imprinting process and shorten the experimental period. The resultant MMIMs displayed fast kinetics and high binding capacity, and the adsorption processes followed Langmuir–Freundlich isotherm and pseudo-second-order kinetic models. Excellent recognition selectivity toward 17β-E2 was attained over other phenolic estrogens such as 17-alpha-E2, estriol and estrone. The magnetic property of MMIMs provided fast and simple separation, and the recycling process for magnetic solid phase extraction (MSPE) was sustainable at least five times without obvious efficiency decrease. Furthermore, the MMIMs-MSPE presented satisfactory recoveries within 71.7–108.3% with the precisions of 1.1–6.0% for spiked 17β-E2 in water, soil and food samples. The developed MMIMs-based method proved to be a convenient and practical way in sample pretreatment and targeted pollutants removal.

Photonic and magnetic dual responsive molecularly imprinted polymers: preparation, recognition characteristics and properties as a novel sorbent for caffeine in complicated samples

We demonstrated the construction and characteristics of photonic and magnetic dual responsive molecularly imprinted polymers (DR-MIPs) prepared by combination of stimuli-responsive polymers and a molecular imprinting technique. The resultant DR-MIPs of Fe3O4@MIPs exhibited specific affinity for caffeine and photoisomerization induced reversible uptake and release of caffeine upon alternate UV and visible light irradiation. With irradiation at 365 nm, 62.5% of the receptor-bound caffeine was released from the DR-MIPs back into solution. Subsequent irradiation with visible light caused 93.6% of the released caffeine to be rebound by the DR-MIPs. The novel DR-MIPs were used as a sorbent for the enrichment of caffeine from real water and beverage samples. Recoveries ranging from 89.5-117.6% were achieved. The magnetic property of DR-MIPs provided fast and simple separation while the photonic responsive property offered simple template elution with the assistance of UV-Vis irradiation. The simple, rapid and reliable DR-MIPs based method proved potentially applicable for trace caffeine analysis in complicated samples.

Hg2+ ion-imprinted polymers sorbents based on dithizone–Hg2+ chelation for mercury speciation analysis in environmental and biological samples

For mercury speciation analysis in environmental and biological samples, novel Hg2+ ion-imprinted polymers (IIPs) were synthesized by a sol-gel process using the chelating agent dithizone, and then dithizone-Hg2+ chelate as a template and 3-aminopropyltriethoxysilane as a functional monomer, followed by solid-phase extraction (SPE) and atomic fluorescence spectroscopy (AFS) detection. The resultant Hg-IIPs offered high binding capacity, fast kinetics, and their adsorption processes followed a Langmuir isotherm and pseudo-second-order kinetic models. The IIPs displayed excellent selectivity toward Hg2+ over its organic forms and other metal ions with selectivity factors of 19-34, as well as high anti-interference ability for Hg2+ confronting with common coexistent ions. Through 10 adsorption-desorption cycles, the IIPs showed a good reusability with a relative standard deviation within 5%. Moreover, because of the chelation of dithizone, the IIPs could readily discriminate Hg2+ from organic mercury. Thus, mercury speciation analysis could be attained by using IIPs-SPE-AFS, presenting high detectability of up to 0.015 mu g L-1 for Hg2+ and 0.02 mu g L-1 for organic mercury. This method was validated by using two certified reference materials with very consistent results. Satisfactory recoveries ranging from 93.0-105.2% were attained for spiked seawater and lake water samples with three concentration levels of Hg2+. Furthermore, the analytical results for the spiked mercury species in real biological samples, such as human hair and fish meat, confirmed that the methods are practically applicable to speciation analysis. The IIPs-SPE-AFS demonstrated significant application perspectives for rapid and high-effective cleanup, enrichment and determination of trace mercury species in complicated matrices.

Chemodosimeter-based fluorescent detection of L-cysteine after extracted by molecularly imprinted polymers.

A chemodosimeter-based fluorescent detection method coupled with molecularly imprinted polymers (MIPs) extraction was developed for determination of L-cysteine (L-Cys) by combining molecular imprinting technique with fluorescent chemodosimeter. The MIPs prepared by precipitation polymerization with L-Cys as template, possessed high specific surface area of 145 m(2)/g and good thermal stability without decomposition lower than 300 °C, and were successfully applied as an adsorbent with excellent selectivity for L-Cys over other amino acids, and enantioselectivity was also demonstrated. A novel chemodosimeter, rhodamine B1, was synthesized for discriminating L-Cys from its structurally similar homocysteine and glutathione as well as various possibly co-existing biospecies in aqueous solutions with notable fluorescence enhancement when adding L-Cys. As L-Cys was added with increasing concentrations, an emission band peaked at 580 nm occurred and significantly increased in fluorescence intensity, by which the L-Cys could be sensed optically. High detectability up to 12.5 nM was obtained. An excellent linearity was found within the wide range of 0.05-50 μM (r=0.9996), and reasonable relative standard deviations ranging from 0.3% to 3.5% were attained. Such typical features as high selectivity, high sensitivity, easy operation and low cost enabled this MIPs-fluorometry to be potentially applicable for routine detection of trace L-Cys.

Determination of polychlorinated biphenyls in seawater using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry with the aid of experimental design

A simple and reliable pretreatment approach in gas chromatography-mass spectrometry (GC-MS) was developed for concurrent clean-up of seawater and the concentration of lipophilic polychlorinated biphenyls (PCBs) with 1-8 chlorine atoms based on the combination of KMnO4 oxidation with headspace sampling and solid-phase microextraction (SPME). Factors affecting the extraction process were studied using a multivariable approach. Under optimum conditions such as PDMS 7 mu m of fiber, 78 degrees C of extraction temperature, 33 min of extraction time, 8 mL of volume, the limits of detection ranged from 0.3 to 7.5 ng L-1 and precisions were between 3.9 and 9.9% at spiked 0.05 mu g L-1 PCBs. Humic acids in seawater exhibited remarkably negative effects; recoveries of PCBs were significantly improved, especially for more lipophilic CB171 and CB201 from 35% and 49% to 78% and 89%, respectively, after KMnO4 pretreating seawater samples at pH 6. The developed method was demonstrated to be simple, rapid, reliable and applicable for determining different PCBs in seawater containing large amounts of humic substances.

ANALYSIS OF URINARY PORPHYRINS BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY-ELECTROSPRAY IONIZATION MASS SPECTROMETRY

A high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS) method was developed for the simultaneous separation and detection of six porphyrins, namely uroporphyrin (UP), heptacarboxylic acid porphyrin (HEPTAP), hexacarboxylic acid porphyrin (HEXAP), pentacarboxylic acid porphyrin (PENTAP), coproporphyrin (CP), and mesoporphyrin (MP), in human urine samples. The recoveries of the porphyrins in urine ranged from 84 to 108%. The intra- and inter-day precisions at spiked porphyrin concentrations were 4.0–9.7% and 5.5–15%, respectively. The limits of detection (LOD) ranged from 0.2 to 3 nM. The developed method was successfully applied to the determination of endogenous porphyrins in human urine. UP, HEPTAP, and PENTAP were detected at levels of 42.4, 21.3, and 18.0 nM, respectively. CP was detected as the predominant species at 135.6 nM, wheres MP and HEXAP were not detected in the urine samples from healthy females. Significant increases of CP excretion in urine from liver disease patients were observed. This method proved potentially applicable for the routine diagnosis and treatment of porphyrin-related diseases.

Simultaneous phase-inversion and imprinting based sensor for highly sensitive and selective detection of bisphenol A

A novel recognition element of molecularly imprinted films (MIFs) was synthesized by wet phase inversion (WPI) on the surface of Ti/TiO2 electrode for highly selective and sensitive electrochemical detection of bisphenol A (BPA). The Ti/TiO2/MIFs sensor was constructed by casting the precursor poly(acrylonitrile-co-acrylic acid) (p(AN-co-AA)) in dimethyl sulfoxide containing template molecule BPA onto the electrode and then immersing into water, resulting in simultaneous p(AN-co-AA) precipitation and BPA imprinting via the facile WPI. The imprinted sites could selectively rebind BPA through hydrogen bonding and hence lead to the equalizing current increase in amperometric detection, by which the BPA could be sensed electrochemically. Accordingly, the Ti/TiO2/MIFs sensor offered a favorable linearity within the wide range over five orders of magnitude (4.4nM-0.13mM), and a low detection limit down to 1.3nM. Excellent recognition selectivity for BPA was also attained over its analogues. Furthermore, this sensor was successfully applied to detect BPA in seawater and paper cup samples, and high recoveries were 86-110% with low relative standard deviations of 1.3-3.2%. By using BPA as a model, the MIFs-based method may provide a facile, rapid, and cost-effective way for ultrasensitive electrochemical measurements of various targeted compounds with good applicability to WPI.