Tianyu Zhou

Rapid microwave-assisted synthesis of molecularly imprinted polymers on carbon quantum dots for fluorescent sensing of tetracycline in milk

In this paper, a novel, selective and eco-friendly sensor for the detection of tetracycline was developed by grafting imprinted polymers onto the surface of carbon quantum dots. A simple microwave-assisted approach was utilized to fabricate the fluorescent imprinted composites rapidly for the first time, which could shorten the polymerization time and simplify the experimental procedure dramatically. The novel composites not only demonstrated excellent fluorescence stability and special binding sites, but also could selectively accumulate target analytes. Under optimal conditions, the relative fluorescence intensity of the composites decreased linearly with increasing the concentration of tetracycline from 20 nM to 14 µM. The detection limit of tetracycline was 5.48 nM. The precision and reproducibility of the proposed sensor were also acceptable. Significantly, the practicality of this ultrasensitive sensor for tetracycline detection in milk was further validated, revealing the advantages of simplicity, sensitivity, selectivity and low cost. This approach combines the high selective adsorption property of molecular imprinted polymers and the sensitivity of fluorescence detection. It is envisioned that the development of fluorescent molecularly imprinted composites will offer a new way of thinking for rapid analysis in complex samples.

Rapid preparation of expanded graphite by microwave irradiation for the extraction of triazine herbicides in milk samples.

In this study, we proposed a rapid and efficient method for the preparation of the expanded graphite (EG). The exfoliation process was accelerated by microwave irradiation, and the preparation time was greatly shortened. The obtained EG was worm-like in shape and exhibits well exfoliated structure. It was successfully applied as solid-phase extraction (SPE) adsorbent to extract and clean up the triazine herbicides in milk, followed by liquid chromatography tandem mass spectrometry (LC-MS) analysis. The parameters affecting the performance of extraction and LC-MS analysis were evaluated. Under the optimal conditions, the detection limits of triazines are in the range of 0.03-0.12 ng mL(-1). At the spiked level (0.4 ng mL(-1)), the recoveries of triazines are in the range of 82.5±2.5% to 97.5±7.5%. The proposed method was successfully applied to determine six triazines in six milk samples.

Preparation of magnetic superhydrophilic molecularly imprinted resins for detection of triazines in aqueous samples

In this work, magnetic superhydrophilic molecularly imprinted resins (MMIRs) were prepared for the determination of triazines in aqueous samples combined HPLC-MS/MS. The amino functionalized magnetic nanoparticles were introduced into superhydrophilic molecularly imprinted resins based on one-pot condensation of resorcinol, melamine and formaldehyde. The obtained MMIRs exhibited magnetic responsiveness, superhydrophilic and selective feature. The MMIRs were directly used as adsorbents for selective enrichment and separation of six triazines in juice and lake samples under an applied magnetic field. The detection limits of triazines are in the range of 0.02-0.07μgL-1 (except for simazine, 0.38μgL-1). At the spiked level (5μgL-1), the recoveries are in the range of 85-101% with the RSDs ≤7%. This work provided a novel and efficient approach for the detection of triazines in aqueous samples.

Multi-throughput dynamic microwave-assisted leaching coupled with inductively coupled plasma atomic emission spectrometry for heavy metal analysis in soil

A rapid and simple multi-throughput dynamic microwave-assisted leaching combined with inductively coupled plasma atomic emission spectrometry determination has been proposed for the simultaneous determination of Cu, Mn, Zn and Pb in soil. The approach combines the advantages of microwave and dynamic leaching technique, and up to five samples could be treated at the same time within 15 min. Nitric acid aqueous solution (20%, w/w) was employed as leachant at a flow rate of 1.5 mL min−1. The leaching condition was optimized systematically and the leaching efficiencies were above 95% for Cu, Mn, Zn, Pb and lower for Cr, Cd, Ni and Co, compared to the conventional method. The leaching efficiencies of Cr, Cd, Ni, and Co could be enhanced to above 60% when a soak process was appended. Relative standard deviations of intra- and inter-day of Cu, Mn, Zn, and Pb were in the range of 1.7–6.3% and 5.0–6.9%, respectively. The proposed method was more rapid than the conventional digestion method and could be an alternative approach for the analysis of heavy metals in complex solid samples. The relatively closed system may have a broad prospect for leaching volatile elements, such as As, Se and Hg if combined with compatible detecting instrumentation.

Determination of triazine herbicides from honey samples based on hydrophilic molecularly imprinted resins followed by high performance liquid chromatography-tandem mass spectrometry

A facile, novel and efficient approach to extract six triazine herbicides from honey samples based on hydrophilic molecularly imprinted resins (MIRs) was described. The MIRs were prepared in a one-pot polycondensation with resorcinol and melamine as the double functional monomers, formaldehyde as a crosslinking agent, and ametryn as the template. The obtained MIRs have a uniform spherical morphology and excellent dispersibility in water due to them having a large number of hydrophilic groups. The MIRs were successfully used as a solid-phase extraction material to rapidly extract and clean up to six triazines in honey samples followed by high performance liquid chromatography-tandem mass spectrometry detection. Under optimal conditions, the method showed higher recoveries and a shorter extraction time. The detection limits of the six triazines are in the range of 0.02–0.15 ng g−1. The recoveries of the six triazines are in the range of 83 ± 4% to 97 ± 4% at the spiked level of 5 ng g−1. The proposed method is simple and quick and has the potential to detect triazine herbicides in other aqueous samples.

Microwave-assisted synthesis of carbon dots for "turn-on" fluorometric determination of Hg(II) via aggregation-induced emission

AbstractA fluorescent probe is presented for sensitive determination of Hg(II). It is based on aggregation induced enhancement effect (AIEE) of carbon dots co-doped with nitrogen and sulfur (N,S-CDs). The N,S-CDs were prepared by a one-pot microwave-assisted method using glycerol as the reaction solvent, and cystine as the source for C, N and S. The resulting CDs are well soluble in water and have a turn-on fluorescence response to Hg(II). The incubation time and ratio of raw materials were optimized. Fluorescence, best measured at excitation/emission wavelengths of 325/385 nm, increases linearly in the 1–75 μM Hg(II) concentration range, and the detection limit is 0.5 μM. The method performed successfully when detecting Hg(II) in spiked tap and lake waters, with recoveries between 92 and 106%. Graphical abstractSchematic presentation of the aggregation induced enhancement of the fluorescence of carbon dots co-doped with nitrogen and sulfur after addition of Hg(II).

Microwave-assisted rapid preparation of monodisperse superhydrophilic resin microspheres as adsorbent for triazines in fruit juices

Monodisperse superhydrophilic melamine formaldehyde resorcinol resin (MFR) microspheres were prepared in 90min at 85°C via a microwave-assisted method with a yield of 60.6%. The obtained MFR microspheres exhibited narrow size distribution with the average particle size of about 2.5µm. The MFR microspheres were used as absorbents to detect triazines in juices followed by high performance liquid chromatography tandem mass spectrometry. Various factors affecting the extraction efficiency were investigated. Under the optimized conditions, the built method exhibited excellent linearity in the range of 1-250μgL-1 (R2 ≥ 0.9994) and lower detection limits (0.3-0.65μgL-1). The relative standard deviations of intra- and inter-day analyses ranged from 3% to 7% and from 2% to 7%, respectively. The method was applied to determine six triazines in three juice samples. At the spiked level of 3μgL-1, the recoveries were in the range of 90-99% with the relative standard deviations ≤ 8%.

Single-Hole Hollow Molecularly Imprinted Polymer Embedded Carbon Dot for Fast Detection of Tetracycline in Honey

It is difficult to detect tetracycline (TC) in honey sample by using carbon dots (CDs) because the autofluorescence of the matrix of honey sample overlaps with the fluorescence emission spectrum of the large majority of CDs. Herein, single-hole hollow molecularly imprinted polymers embedded carbon dots (HMIP@CD) was prepared via microwave-assisted method. TC in diluted honey sample was adsorbed by the HMIP@CD within 3 min, after which the HMIP@CD absorbed with TC was separated by centrifugation from honey sample and redispersed into phosphate buffer solution. The autofluorescence of honey that interferes with the fluorescence signal of HMIP@CD was avoided. The method exhibited an excellent linearity within 10-200 μg L-1 and a low detection limit of 3.1 μg L-1. At three spiking levels of TC, the recoveries ranged from 93% to 105% with precisions below 1.6%. This method provides an effective strategy for detecting analyte in complex matrix with autofluorescence interference.

Microwave-assisted preparation of boron acid modified expanded graphite for the determination of chloramphenicol in egg samples

A rapid and simple method for the synthesis of boron acid modified expanded graphite (B-EG) with the assist of microwave irradiation was developed. The synthesis process can be completed in one-step, where H2SO4 and H3BO3 were used as intercalating agent and KMnO4 was used as oxidizing agent. The obtained B-EG was worm-like and lamellar structure with plenty of small dispersed particles. The B-EG was successfully used as solid phase extraction absorbent for the enrichment and separation of chloramphenicol in egg samples, followed by liquid chromatography tandem mass spectrometry analysis. The predominant conditions affecting extraction efficiency were optimized. Under optimal conditions, the detection limit of the method was 0.27 ng g-1. The relative standard deviations of within-day and between-day were in the range of 2-6% and 2-8%, respectively. The method was successfully used to detect chloramphenicol in five egg samples. At the spiked concentration of 50 ng g-1, the satisfactory recoveries (87-94%) were obtained.

Preparation of magnetic surface molecularly imprinted polymers for the selective extraction of triazines in environmental water samples

ABSTRACT In this work, a magnetic molecularly imprinted polymer (Fe3O4@SiO2@MIPs) was prepared via a surface-imprinted method for the determination of the triazines in environmental water samples combined with high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer showed that the Fe3O4@SiO2@MIPs was successfully synthesised and exhibited superparamagnetism. The isotherm adsorption, selectivity and adsorption kinetics experiments showed that the Fe3O4@SiO2@MIPs exhibited excellent specific recognition and fast adsorption equilibrium for triazines. The adsorption process is spontaneous and endothermic. The isotherm adsorption was consistent with Scatchard model and adsorption kinetic fit pseudo-second-order kinetic model. Under the optimised adsorption conditions, the Fe3O4@SiO2@MIPs was directly used to selectively enrich six triazines in environmental water samples. The enrichment volume was up to 500 mL, and the matrix effects were down to 0.7–12.4%. The built method has excellent linearities in the range of 0.25–500 ng L−1 with R2 in the range of 0.998–0.999, lower limit of detections (0.02–0.08 ng L−1) and higher precision (2.4–7.2%). The Fe3O4@SiO2@MIPs is expected to be widely applied to the direct enrichment of triazines in bulk environmental water samples.