Lixia Zhao

Molecularly imprinted solid-phase extraction for the selective determination of 17β-estradiol in fishery samples with high performance liquid chromatography.

A molecularly imprinted polymer (MIP) has been synthesized by a thermo-polymerization method using methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, acetonitrile as porogenic solvent, and 17beta-estradiol as template. The MIP showed obvious affinity for 17beta-estradiol in acetonitrile solution, which was confirmed by absorption experiments. After optimization of molecularly imprinted solid-phase extraction (MISPE) conditions, three structurally related estrogenic compounds (17beta-estradiol, estriol, and diethylstilbestrol) were used to evaluate the selectivity of the MIP cartridges. The MIP cartridges exhibited highly selectivity for E(2), the recoveries were 84.8+/-6.53% for MIPs and 19.1+/-1.93% for non-imprinted polymer (NIP) cartridges. The detection and quantification limits correspond to 0.023 and 0.076 mg L(-1). Furthermore, the MISPE methods were used to selectively extract E(2) from fish and prawn tissue prior to HPLC analysis. This MISPE-HPLC procedure could eliminate all matrix interference simultaneously and had good recoveries (78.3-84.5%).

Molecularly imprinted polymer as micro-solid phase extraction combined with high performance liquid chromatography to determine phenolic compounds in environmental water samples

The molecularly imprinted polymer with 2,4,6-trichlorophenol (2,4,6-TCP) as the template molecule and methylacrylic acid (MAA), divinylbenzene (DVB) as functional monomer and the crosslinker, respectively, has been prepared and used as molecularly imprinted micro-solid phase extraction (MIMSPE) procedure for the selectively preconcentration of phenolic compounds from environmental water samples. Various parameters for the extraction efficiency of the MIMSPE have been evaluated. The optimized MIMSPE method allowed the extraction of the analytes from the sample matrix followed by a selective washing step using acetonitrile containing 0.3% (v/v) acetic acid. The characteristics of the MIMSPE method were valid by high performance liquid chromatography. The recoveries ranged between 88.9% and 102.5% for tap water, between 80.0% and 94.0% for river water, between 80.0% and 90.5% for sewage water fortified with 0.4 mg L(-1) of phenol, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-TCP, pentachlorophenol (PCP) were obtained. This method has been successfully applied to preconcentrate and determine of phenolic compounds in environmental water samples directly.

Molecularly imprinted solid-phase extraction combined with high performance liquid chromatography for analysis of phenolic compounds from environmental water samples

The molecularly imprinted bulk polymer with 2,4,6-trichlorophenol (2,4,6-TCP) as the template molecule and methylacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA) as functional monomer and the crosslinker, respectively, has been prepared and applied to the molecularly imprinted solid-phase extraction (MISPE) procedure for selective preconcentration of phenolic compounds from environmental water samples. Various parameters affecting the extraction efficiency of the polymer have been evaluated to optimize the selective preconcentration of the phenolic compounds from aqueous samples. The characteristics of the MISPE method were validated by HPLC. The recoveries ranged between 90% and 98% (RSD: 0.9-2.3%, n=3) for tap water, between 85% and 105% (RSD: 2.6-4.9%, n=3) for river water, between 78% and 98% (RSD: 2.6-5.4%, n=3) for sewage water fortified with 0.4 mg L(-1) of phenol, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), pentachlorophenol (PCP). It was demonstrated that this MISPE-HPLC method could be applied to direct preconcentration and determination of phenolic compounds in environmental water samples.

Experimental studies on the chemiluminescence reaction mechanism of carbonate/bicarbonate and hydrogen peroxide in the presence of cobalt(II)

Chemiluminescence (CL) phenomena of carbonates or bicarbonates of potassium, sodium, or ammonium with hydrogen peroxide in the presence of cobalt sulfate were reported. After cobalt(II) solution was injected into the mixture of carbonate/bicarbonate and hydrogen peroxide, a CL signal was given out briefly. The CL conditions of these systems were optimized. The CL reaction mechanisms were studied experimentally by examining the spectrum emitted by the CL system and the effect of various free radical scavengers on CL emission intensity. The results showed that the maximal emission wavelengths of the CO32--H2O2-Co2+ and HCO3--H2O2-Co2+ systems were 440 and 490 nm, respectively. As a result, a radical scavenger of ascorbic acid, thiourea, and superoxide dismutase exhibited different effects on these CL systems. The different CL mechanisms involving the carbon dioxide dimer and the oxygen dimer were revealed, respectively.

Determination of folic acid by chemiluminescence based on peroxomonosulfate-cobalt(II) system

Based on the chemiluminescence (CL) phenomena of folic acid in peroxomonosulfate-cobalt(II) system, a rapid and sensitive CL method was developed for determination of folic acid in pharmaceutical preparations and its urinary metabolism processes. Under the optimum conditions, the relative CL intensity was linear over the concentration ranging from 10(-9) to 8 x 10(-7)molL(-1) (R(2)=0.9991) with a detection limit as low as 6 x 10(-10)molL(-1) (S/N=3) and relative standard deviation was 2.63% for 2 x 10(-8)molL(-1) folic acid (n=11). This method has been successfully applied to the determination of folic acid in tablets and human urine. The blank CL emission was yielded owing to the formation of singlet oxygen molecular pair from the quenching experiment of 1,4-diazabicyclo[2.2.2]octane, and pterine-6-carboxylic acid might be the degradation intermediate in this system and it also acts an energy acceptor and sensitizes the chemiluminescence based on the studies of the CL and fluorescence spectra.

Gold nanorod-catalyzed luminol chemiluminescence and its selective determination of glutathione in the cell extracts of Saccharomyces cerevisiae

In this study, gold nanorods were firstly found to exhibit a tremendously higher catalytic activity towards luminol chemiluminescence (CL) than spherical gold nanoparticles. More importantly, ultra-trace aminothiols can cause a great CL decrease in the gold nanorod-catalyzed luminol system by the formation of Au-S covalent bonds on the ends of gold nanorods. Aminothiols can occupy the active sites of gold nanorods, and further interrupt the generation of the active oxygen intermediates. Other biomolecules including 19 standard amino acids, alcohols, organic acids and saccharides have no effect on gold nanorod-catalyzed luminol CL signals. Moreover, in order to evaluate the applicability and reliability of the proposed method, it was applied to the determination of glutathione in the cell extracts of Saccharomyces cerevisiae. Good agreements were obtained for the determination of glutathione in the cell extracts of S. cerevisiae between the present approach and a standard Alloxan method. The recoveries of glutathione were found to fall in the range between 96 and 105%. The calibration curve for glutathione was found to be linear from 0.05 to 100 nM, and the detection limit (S/N=3) was 0.01 nM. The relative standard deviation (RSD) for five repeated measurements of 5.0 nM glutathione was 2.1%.

CdTe nanocrystals-enhanced chemiluminescence from peroxynitrous acid–carbonate and its application to the direct determination of nitrite

It was found that CdTe semiconductor nanocrystals (NCs) can induce a great sensitized effect on chemiluminescence (CL) emission from peroxynitrous acid (ONOOH)-Na(2)CO(3) system. CL spectra, fluorescence (FL) spectra, and the quenching effect of reactive oxygen species were used to investigate the CL reaction mechanism. The CL intensity was proportional to the concentration of nitrite in the range from 0.05 to 50μM. The detection limit (S/N=3) was 0.024μM and the relative standard deviation (RSD) for five repeated measurements of 0.5μM nitrite was 4.2%. This method has been successfully applied to determine nitrite in well water samples with recoveries of 94.0-100.5%. This was the first work for direct (not inhibition effect) determination of analytes using semiconductor NCs-based CL sensor.

A selective optical chemical sensor for 2,6-dinitrophenol based on fluorescence quenching of a novel functional polymer.

A bifurcated optical fiber based chemical sensor for continuous monitoring of 2,6-dinitrophenol (2,6-DNP) has been proposed based on the reversible chemical reaction between a novel functional poly(vinyl chloride) (PVC) as the sensing material and the analytes. The functional PVC (FPVC), containing a fluorescent curcumin moiety, was synthesized by the nucleophilic substitution of a fraction of the chlorine atoms bound to the PVC backbone by curcumin. When plasticized in a membrane of 5mum thickness, FPVC extracts 2,6-DNP from aqueous solution into the bulk membrane phase and reacts with the analyte to form a complex with low fluorescence efficiency through hydrogen bonding. Formation of the complex gave a significant fluorescence quenching which is suitable for signalling the occurrence of the host-guest interaction. At pH 3.50, the sensor exhibits a dynamic detection range from 2.5x10(-6) to 7.0x10(-3)molL(-1) with a limit of detection of 1.0x10(-6)molL(-1). As 2,6-DNP can provide an optimal space geometry matches to the formation of hydrogen bonds, the sensor shows excellent selectivity for 2,6-DNP over other nitrophenols. The forward and reverse response time (t(95)) of the sensor both was within 1min. The repeatability, reproducibility, and lifetime of the sensor were also satisfied. The sensor was applied to determine 2,6-DNP in water samples successfully.

Study on superoxide and hydroxyl radicals generated in indirect electrochemical oxidation by chemiluminescence and UV-Visible spectra

The generation and transformation of radicals on the cathode of indirect electrochemical oxidation were studied by chemiluminescence (CL) and UV-Visible spectra in the reactor with a salt bridge that connected the separated chambers. The CL intensity of 4 x 10(-9) mol/L luminol on the cathode with bubbling oxygen was about seven times that of the intensity without it, which was because of the generation of reactive oxygen species (ROS). The existence of ROS, especially the generation of the superoxide radical, could be affirmed by the fact that the CL intensity of 4 x 10(-9) mol/L 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo[1,2-a]pyrazin-3-one with bubbling oxygen was about four times that of the intensity without it. However, there was no chemiluminescence on the anode under the same condition. The change in the UV-Visible spectra of nitro blue tetrazolium and N,N-dimethyl-4-nitrosoaniline at the cathode chamber affirmed the transformation from oxygen to superoxide and hydroxyl radicals. The mechanism of the superoxide and hydroxyl radical generation and transformation on the cathode was discussed with the help of the experimental results and relative references.

Fluorosurfactant-capped gold nanoparticles-enhanced chemiluminescence from hydrogen peroxide-hydroxide and hydrogen peroxide-bicarbonate in presence of cobalt(II)

Nonionic fluorosurfactant (FSN)-capped gold nanoparticles (GNPs) remain excellently stable at a wider pH range and high ionic strength, which is useful to investigate some CL systems involved in high salt and a strict pH range. In this study, we utilized FSN-capped GNPs of different sizes to distinguish the emitting species from H2O2-Co2+-NaOH and H2O2-Co2+-NaHCO3 systems. When the pH of FSN-capped gold colloidal solution was adjusted to 10.2 by dropwise addition of 0.05 M NaOH, the CL intensity of H2O2-Co2+-NaHCO3 system was enhanced 6-fold or 60-fold respectively in the presence of FSN-capped 14 nm or 69 nm GNPs with comparison to H2O2-Co2+-NaOH. The variation of CL spectra and UV-vis spectra, as well as the quenching effect of reactive oxygen species scavengers were studied in detail to understand the CL enhancement mechanisms of FSN-capped GNPs on the two systems. For H2O2-Co2+-NaOH system, the gold(I) complexes intermediate and singlet oxygen dimol species were proposed as the emitting species. The excited states of the carbon dioxide dimers and singlet oxygen dimol species were considered responsible for the light emission of H2O2-Co2+-NaHCO3 system. To our knowledge, this work is the first time to study the two CL systems simultaneously using nanoparticles.