Jingdong Peng

Photo-responsive molecularly imprinted hydrogels for the detection of melamine in aqueous media

In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 × 104 M−1 in aqueous Tris–HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 μmol g−1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.

Ultrasensitive detection of bisphenol A in aqueous media using photoresponsive surface molecular imprinting polymer microspheres

Photoresponsive surface molecular imprinting polymer (SMIP) microspheres were synthesized on silica microspheres by surface polymerization using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid as the functional monomer. The SMIP microspheres displayed good photoresponsive properties and specific affinity towards bisphenol A (BPA) with high recognition ability (maximal adsorption capacity: 6.96 μmol g−1) and fast binding kinetics (binding constant: 2.47 × 104 M−1) in aqueous media. Upon alternate irradiation at 365 and 440 nm, the SMIP microspheres could quantitatively bind and release BPA. Analytical application of the SMIP microspheres for the detection of trace BPA concentration in mineral water and tap water has been carried out successfully, and therefore a simple and quick detection method for trace BPA in the environment was established.

Fluorescent carbon dots for the sensitive detection of Cr(VI) in aqueous media and their application in test papers

Chromium(VI) is proved to be highly carcinogenic and mutagenic, thus sensitive and rapid sensors for monitoring Cr(VI) are in urgent demand. In this work, a facile fluorescent assay for the sensitive and selective detection of Cr(VI) was proposed based on static quenching combined with inner filter effect (IFE) using phosphate functionalized carbon dots (PCDs) as nanoprobes. A good linear quenching was observed in the range of 1.0–400 μM with a detection limit of 0.24 μM (σ/S = 3) under the optimized conditions. The nanoprobe was employed for detecting Cr(VI) in real water samples including river water and tap water with satisfactory recovery. Moreover, with the addition of Cr(VI), the color changes of PCDs can be easily observed by the naked eye under a UV lamp. Based on this, Cr(VI) test papers were fabricated for spot quick detection of Cr(VI).

Preparation and evaluation of surface molecularly imprinted polymers as stationary phase columns for high performance liquid chromatography

Herein, highly selective surface molecularly imprinted polymers (SMIPs) were prepared on the surface of silica microspheres and employed as a new stationary phase for high performance liquid chromatography (HPLC). In this paper, myricetin was selected as the template and successfully grafted onto the derivatized silica particles (size: 5 μm), and acetonitrile/methanol were used as the porogen and co-solvent. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermo-gravimetric analysis (TGA) were used as characterization measures, and the results illustrated that the polymers were successfully synthesized. The obtained uniform polymer particles were packed in stainless steel columns (250 mm × 4.6 mm) and evaluated as the imprinted stationary phase. Then the packed columns were connected to an Agilent 1100 series HPLC system to separate a mixture of four flavonoids. The SMIP stationary phase showed a good effect on the separation of the flavonoid mixture.

The fluorescence and resonance Rayleigh scattering spectra study on the interactions of palladium (II)-Nootropic chelate with Congo red and their analytical applications

A highly sensitive detection approach of resonance Rayleigh scattering spectra (RRS) is firstly applied to analyzing nootropic drugs including piracetam (PIR) and oxiracetam (OXI). In HCl-NaAc buffer solution (pH=3.0), the OXI chelated with palladium (II) to form the chelate cation [Pd2·OXI]2+, and then reacted with Congo red (CGR) by virtue of electrostatic attraction and hydrophobic force to form binary complex [Pd2·OXI]. CGR2, which could result in the great enhancement of RRS. The resonance Rayleigh scattering signal was recorded at λex=λem=375nm. This mixture complex not only has higher RRS, but also makes contribution to significant increase of fluorescence, and the same phenomena also were discovered in PIR. The enhanced RRS intensity is in proportion to the PIR and OXI concentration in the range of 0.03-3.0μgmL-1, and the detection limit (DL) of RRS method for PIR and OXI is 2.3ngmL-1 and 9.7ngmL-1. In addition, the DL of fluorescence method for PIR and OXI is 8.4μgmL-1 and 19.5μgmL-1. Obviously, the RRS is the highly sensitive method, and the recoveries of the two kinds of nootropic drugs were range from 100.4% to 101.8.0% with RSD (n=5) from 1.1% to 3.1% by RRS method. This paper not only investigated the optimum conditions for detecting nootropics with using RRS method, but also focused on the reasons for enhancing RRS intensity and the reaction mechanism, which in order to firm and contract the resultant. Finally, The RRS method has been applied to detect nootropic drugs in human urine samples with satisfactory results.

Preparation and evaluation of surface-bonded phenylglycine zwitterionic stationary phase

Abstract4-Hydroxy-d-phenylglycine was modified with methacrylic anhydride and then immobilized on silica through thiol-initiated surface polymerization; the prepared material was applied as stationary phase for HPLC. The obtained stationary phase was characterized by elemental analysis, infrared spectroscopy, and thermogravimetric analysis. The chromatographic performance of the packed column was evaluated in reversed-phase liquid chromatograph (RPLC) and hydrophilic interaction liquid chromatograph (HILIC) mode; this column has shown excellent selectivity to both the hydrophobic and hydrophilic solutes. The selectivity towards polycyclic aromatic hydrocarbons relative to that towards alkylbenzenes exhibited by the prepared column was higher than the corresponding selectivity exhibited by commercial C18 column, which could be explained by electronic π-π interaction between phenylglycine and electron-rich aromatic rings. On the other hand, the prepared column has also shown better selectivity for polar compounds, which was based on the multiple interaction and retention mechanisms. It was also used to separate sulfonamides and organic acid compared with a commercial C18 and HILIC column; the results show its great chromatographic performance with distinctive selectivity. All the results indicated the prepared column had potential application in a wide range.

Resonance Rayleigh scattering technique as a detection method for the RP‐HPLC determination of local anaesthetics in human urine

A highly selective and sensitive method of reversed phase high-performance liquid chromatography (RP-HPLC) coupled with resonance Rayleigh scattering (RRS) was developed for the determination of procaine, bupivacaine and tetracaine. Separation of three local anaesthetics was achieved at 35 °C on a C18 column. The mobile phase was 30: 70 (v/v) acetonitrile/triethylamine-phosphoric acid buffer (pH 2.9) at flow rate of 0.3 mL/min. The RRS detection was conducted by taking advantage of the strong RRS enhancement of the local anaesthetics with erythrosine reaction in an acidic medium. Under optimum conditions, the limit of detection (S/N = 3) values were in the range of 2.4-11.2 ng/mL. Recoveries from spiked human urine samples were 95.8%-104.5%. The proposed method applied to the determination of local anaesthetics in human urine achieved satisfactory results. In addition, the mechanism of the reaction is fully discussed. Copyright