Haifang Li

Magnetic solid-phase extraction based on octadecyl functionalization of monodisperse magnetic ferrite microspheres for the determination of polycyclic aromatic hydrocarbons in aqueous samples coupled with gas chromatography-mass spectrometry

Monodisperse magnetic C(18) microspheres were prepared based on the three-step reactions of solvothermal reduction, silanization and alkylation. The microspheres are of uniform sizes in the range of 200-260 nm. The structure of synthesized magnetic C(18) microspheres was studied by transmission electron microscopy, scanning electron microscopy, X-ray diffraction patterns, element analysis and vibrating sample magnetometry. This material has a high magnetic saturation value of 59 emicrog(-1) and is easy to manipulate under a magnet. The prepared material was used for the preconcentration of the polycyclic aromatic hydrocarbon in water. The effects of desorption solvent and the amount of adsorbent on the preconcentration were also investigated. The results showed that the developed method was beneficial for the preconcentration of PAHs of middle molecular weight.

Application of carbon-based nanomaterials in sample preparation: a review.

In this paper, a broad overview on the applications of different carbon-based nanomaterials, including nanodiamonds, fullerenes, carbon nanotubes, graphene, carbon nanofibers, carbon nanocones-disks and nanohorns, as well as their functionalized forms, in sample preparation is provided. Particular attention has been paid to graphene because many papers regarding its application in this research field are becoming available. The distinctive properties, derivatization methods and application techniques of these materials were summarized and compared. According to their research status and perspective, these nanomaterials were classified in four groups (I: graphene and carbon nanotubes; II: carbon nanofibers; III: fullerenes; and IV: nanodiamonds, carbon nanocones/disks and carbon nanohorns) and characteristics and future trends of every group were discussed.

Chip-based enantioselective open-tubular capillary electrochromatography using bovine serum albumin-gold nanoparticle conjugates as the stationary phase

In this study, chip‐based enantioselective open‐tubular CEC (OT‐CEC) was developed employing BSA‐gold nanoparticle (GNP) conjugates as a chiral stationary phase. An immobilization procedure was realized by prederivatization of the glass microchannel with (3‐mercaptopropyl)‐trimethoxysilane to provide thiol groups, which linked the BSA‐GNP conjugates on the inner surface of the microchannels. Incorporation of GNPs into immobilization of BSA selectors greatly increased the BSA phase ratio and favored the BSA stationary phase generated sufficient EOF. Good resolutions of FITC‐labeled ephedrine and norephedrine isomers were achieved with 36 mm effective separation channel length within 250 s. The constructed OT‐CEC microdevice exhibited good repeatabilities for run‐to‐run enantioseparations and kept an enantioselective lifetime of more than 1 month. The effects of pH values and concentrations of a running buffer on the selectivity and resolution of enantioseparations were investigated.

Applications of microfluidic systems in environmental analysis.

During the past few decades, rapid growth in the applications of microfluidic systems to environmental analysis or environmentally related species has been observed. This review presents and critically discusses the published literature on the applications of microfluidic systems to real environmental samples or samples simulating environmental conditions. The subjects covered include integrated pretreatments, separation modes, detection methods and monitoring sensors used in these platforms. The main challenges in this field and the author’s perspectives on future directions for environmental analysis based on microfluidic systems are also proposed.

Determination of ammonia in water based on chemiluminescence resonance energy transfer between peroxymonocarbonate and branched NaYF4:Yb3+/Er3+ nanoparticles.

The ultraweak chemiluminescence (CL) from the reaction of hydrogen peroxide and carbonate is strongly enhanced by the branched NaYF(4):Yb(3+)/Er(3+) nanoparticle (NP) in the presence of aqueous ammonia. It was explained that ammonia catalyzes the decomposition of peroxymonocarbonate, which is the product of hydrogen peroxide mixing with bicarbonate, making the formation of (CO(2))(2)*, (O(2))(2)*, and (1)O(2). The excitation energy, carried by these emitter intermediates, can be transferred to NaYF(4):Yb(3+)/Er(3+) NP. The CL intensity is directly proportional to the concentration of ammonia present in the solution. A flow-injection CL system with high sensitivity, selectivity, and reproducibility is proposed for the determination of aqueous ammonia. The proposed method exhibited advantages in a larger linear range from 0.5 μmol L(-1) to 50 μmol L(-1) and a lower detection limit of 1.1 × 10(-8) mol L(-1) (S/N = 3). This method has been successfully applied to the evaluation of ammonia in water samples with recoveries from 95% to 108%. The relative standard deviations are 1.8% and 4.1% for intra-assay and inter-assay precision, respectively.

Determination of chromium(III) and total chromium using dual channels on glass chip with chemiluminescence detection.

A simple, rapid and sensitive method for the determination of chromium(III) and total chromium using the simple dual T channels on glass chip with negative pressure pumping system and chemiluminescence (CL) detection is presented. The CL reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by chromium(III). Total chromium in form of chromium(III) was achieved after chromium(VI) was completely reduced by acidic sodium hydrogen sulfite. Total chromium could then be determined with the same strategy as the chromium(III). The CL reagent was composed of 1.0x10(-4)mol/L luminol, 1.0x10(-2)mol/L hydrogen peroxide and 0.10mol/L sodium bromide in 0.050mol/L carbonate buffer (pH 11.00). The 1.0x10(-2)mol/L ethylenediaminetetraacetic acid was added into the sample solution in order to improve the selectivity. Chromium(III) could be detected at a notably concentration of 1.6x10(-16)mol/L and a linear calibration curve was obtained from 1.0x10(-15) to 1.0x10(-13)mol/L. The sample and CL reagent consumption were only 15 and 20microL, respectively. The analysis time was less than 1 min per sample with the precision (%R.S.D.) was 4.7%. The proposed method has been applied successfully to the analysis of river water, mineral waters, drinking waters and tap water. Its performance was verified by the analysis of certified total chromium-reference materials and by recovery measurement on spiked synthetic seawater sample.

Determination of parabens in cosmetic products by solid‐phase microextraction of poly(ethylene glycol) diacrylate thin film on fibers and ultra high‐speed liquid chromatography with diode array detector

The fabrication of a solid-phase microextraction (SPME) fiber through UV-induced polymerization of poly(ethylene glycol) diacrylate (PEG-DA) for determination of parabens in cosmetic products is presented in this work. The PEG-DA polymer coating was covalently attached to the fiber by introducing a surface modification with 3-(trichlorosilyl)propyl methacrylate (TPM). The PEG-DA polymer thin film coated on the fiber was homogeneous and wrinkled, which led to an increase of the surface area and high extraction efficiency. The extraction performances of the prepared SPME fibers were assessed by preconcentration of parabens including methylparaben, ethylparaben, propylparaben and benzylparaben from cosmetic products. The analysis was performed on an ultra high-speed liquid chromatography with diode array detector. The prepared SPME fibers exhibited good repeatability (for one fiber) and reproducibility (fiber-to-fiber) with RSDs of 5.4 and 6.9%, respectively. The optimized SPME method supported a wide linear range of 0.50-160 μg/mL and the detection limits for parabens were in the range of 0.12-0.15 μg/mL (S/N=3). The developed method was successfully applied for determination of parabens in cosmetic products with different natures.

Determination of estradiol in human serum using magnetic particles-based chemiluminescence immunoassay

A magnetic particles (MPs)-based chemiluminescence immunoassay (CLIA) with high sensitivity, specificity, and reproducibility was proposed for the evaluation of estradiol (E(2)) in human sera. The MPs coated with secondary antibody were used as dispersed solid phase for the immunoassay, and the horseradish peroxidase (HRP)-luminol-H(2)O(2) chemiluminescent system with high sensitivity was chosen as the detection system. The method showed specific recognition to E(2), without cross-reaction for the major steroids, including estrone (E(1)), estriol (E(3)), dihydrotestosterone (DHT), androstenedione, and testosterone (T), which was commonly found in human serum. The addition of sodium trichloracetate (Na-TCA) in the enzyme buffer as a blocking agent contributed to the realization of direct analysis of E(2) in human serum without extraction. Besides, the effects of several physicochemical parameters, including the dilution ratios of E(2)-6-HRP conjugate and anti-E(2) polyclonal antibody, immunoreaction time, chemiluminescent (CL) substrate volume, volume of MPs, and CL reaction time, were studied and optimized. The proposed method had a detection limit of 2.51pgmL(-1) with a larger working range of 15-1000pgmL(-1). The inter-assay and intra-assay coefficient of variation (CV) were both less than 15%. The average recoveries of three different spiked concentration samples were 93.3, 106 and 101%, respectively. The method has been successfully applied to the determination of E(2) in 105 human sera and showed a good correlation compared with the commercial radioimmunoassay (RIA) kit with a correlative coefficient of 0.9892. This method has exhibited great potential in the fabrication of diagnostic kit and could be used in the clinical analysis of E(2) in human serum.

Nitrite sensing based on the carbon dots-enhanced chemiluminescence from peroxynitrous acid and carbonate

In this work, chemiluminescence (CL) from peroxynitrous acid (ONOOH)-carbonate system greatly amplified by carbon dots was observed. The CL mechanism of the ONOOH-carbonate-carbon dots system has been investigated and the results reveal that the carbon dots could serve as the energy acceptor, which gives us new insight into the optical properties of the new emerging carbon nanomaterial. There is a good linear relationship between the CL signal and the concentration of the nitrite using for ONOOH formation, which provides us a nitrite sensing method with sensitivity as high as 5.0×10(-9) M (S/N=3). The method has been successfully applied to the determination of nitrite in tap water with the recovery of 98%. The standard deviations are within 2.5%.

Aggregation-Induced Structure Transition of Protein-Stabilized Zinc/Copper Nanoclusters for Amplified Chemiluminescence

A stable, water-soluble fluorescent Zn/Cu nanocluster (NC) capped with a model protein, bovine serum albumin (BSA), was synthesized and applied to the reaction of hydrogen peroxide and sodium hydrogen carbonate. A significantly amplified chemiluminescence (CL) from the accelerated decomposition of peroxymonocarbonate (HCO4(-)) by the nanosluster was observed. The CL reaction led to a structure change of BSA and aggregation of Zn/Cu NCs. In the presence of H2O2, Zn/Cu-S bonding between BSA scaffolds and the encapsulated Zn/Cu@BSA NC was oxidized to form a disulfide product. Zn/Cu@BSA NCs were prone to aggregate to form larger nanoparticles without the protection of scaffolds. It is revealed that the strong CL emission was initiated from the catalysis of Zn/Cu@BSA NC and the surface plasmon coupling of the formed Zn/Cu nanoparticles in a single chemical reaction. This amplified CL was successfully exploited for selective sensing of hydrogen peroxide in environmental samples.