Biomedical subjects

Jingcun Wu

Publications and source records attributed to Jingcun Wu.

4 recordsLinked to original sources

PubMed2002

Analysis of polar pesticides in water and wine samples by automated in-tube solid-phase microextraction coupled with high-performance liquid chromatography-mass spectrometry.

A simple and sensitive method for the determination of polar pesticides in water and wine samples was developed by coupling automated in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS). To achieve optimum performance, the conditions for both the in-tube SPME and the ESI-MS detection were investigated. In-tube SPME conditions were optimized by selecting the appropriate extraction parameters, especially the stationary phases used for SPME. For the compounds studied, a custom-made polypyrrole (PPY)-coated capillary showed superior extraction efficiency as compared to several commercial capillaries tested, and therefore, it was selected for in-tube SPME. The influence of the ethanol content on the performance of in-tube SPME was also investigated. It was found that the amount of pesticides extracted decreased with the increase of ethanol content in the solutions. The ESI-MS detection conditions were optimized as follows: nebulizer gas, N2 (30 p.s.i.; 1 p.s.i.=6894.76 Pa); drying gas, N2 (10 l/min, 350 degrees C); capillary voltage, 4500 V; ionization mode, positive; mass scan range, 50-350 amu; fragmentor voltage, variable depending on the ions selected. Due to the high extraction efficiency of the PPY coating and the high sensitive mass detection, the detection limits (S/N = 3) of this method for the compounds studied are in the range of 0.01 to 1.2 ng/ml, which are more than one order of magnitude lower than those of the previous in-tube SPME-HPLC-UV method. A linear relationship was obtained for each analyte in the concentration range of 0.5 to 200 ng/ml with MS detection. This method was applied to the analysis of phenylurea and carbamate pesticides in spiked water and wine samples.

Automation↗

PubMed2002

Electrochemically controlled solid-phase microextraction based on conductive polypyrrole films.

Solid-phase microextraction (SPME) fiber coatings based on conductive polypyrrole films were prepared for the electrochemical extraction and desorption of ionic analytes. Simple preparation of each of the PPY extraction coatings on a platinum wire was possible with a constant potential method, but more importantly, cycling of the film between oxidation and reduction potentials facilitated the extraction and desorption of ionic analytes. The analytes were desorbed into a sample aliquot of water and were determined by flow injection analysis using a mass spectrometer. The fiber coatings and the developed electrochemical SPME method were found to be stable and reproducible (RSD < 5%; N = 5) and could be extended to several cations and anions, confirming the versatility of the approach. Preconcentration of the analyte on the fiber was also possible by repeating the processes to increase the amount of analyte extracted.

Letter↗

PubMed2002

Automated in-tube solid-phase microextraction coupled with HPLC for the determination of N-nitrosamines in cell cultures.

An automated in-tube solid-phase microextraction (SPME) HPLC analysis method for 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and several metabolites has been developed. NNK is one of the tobacco-specific N-nitrosamines (TSNA), which has been linked to cancers associated with the use of or exposure to tobacco products. In-tube SPME is an on-line extraction technique in which analytes are extracted and concentrated from the sample directly into a coated capillary by repeated draw/eject steps. In this study, a tailor-made polypyrrole (PPY)-coated capillary and several commercially available capillaries (capillary GC columns) were used to evaluate their extraction efficiencies for NNK and several metabolites in cell cultures. Compared with commercial capillaries that were currently used for in-tube SPME, the PPY-coated capillary showed better extraction efficiency for all of the compounds studied. After optimization of the extraction conditions, NNK and five metabolite compounds were analyzed in spiked cell cultures, confirming the applicability of the developed method. Excellent linearity was observed for all compounds (av R2 = 0.9942) and detection limits that ranged from 20 to 250 ng/mL. The average within-day and between day variations (% RSD) were 2.9 and 3.6%, respectively. This automated extraction and analysis method simplified the determination of the TSNA, requiring a total sample analysis time of only approximately 30 min.

Animals↗

PubMed1999

Photoelectron Spectra of Trimethylphosphine-Substituted Tungsten Carbonyls: Ligand Field Effects, Ligand Additivity Effects, and Core-Valence Ionization Correlations.

High-resolution broad-scan gas-phase photoelectron spectra using synchrotron radiation (including valence, inner valence, and core levels) are reported for a series of trimethylphosphine-substituted tungsten carbonyls: W(CO)(6), W(CO)(5)PMe(3), cis-W(CO)(4)(PMe(3))(2), trans-W(CO)(4)(PMe(3))(2), and fac-W(CO)(3)(PMe(3))(3). The inner valence and core level spectra are interpreted by comparison with the published spectra of W(CO)(6) and other metal carbonyls. High-resolution valence level spectra of these complexes are also obtained by He I radiation. Fine structure, resulting from spin-orbit splitting, ligand field splittings, and vibrational coupling is resolved in the spectra of both W 5d and W 4f regions. Ligand field splittings on both the W 5d and W 4f levels increase in the order W(CO)(6) approximately fac-W(CO)(3)(PMe(3))(3) < W(CO)(5)PMe(3) </= cis-W(CO)(4)(PMe(3))(2) < trans-W(CO)(4)(PMe(3))(2). For the first time, the phosphorus 2p spin-orbit components of the phosphine complexes have been resolved. The binding energies (or ionization potentials) in the spectra of both W 5d valence level and W 4f core level regions are shifted almost linearly to lower energy with each successive step of ligand substitution. The shift per phosphine substitution is 0.66 +/- 0.03 eV for the W 5d ionizations and 0.76 +/- 0.03 eV for the W 4f ionizations (DeltaE(valence)/DeltaE(core) = 0.86 +/- 0.03). Similar linear shift trends are also found in the phosphorus 2p core level and phosphorus valence "lone-pair" ionizations. These data confirm the ligand additivity model predictions for these complexes.

Journal Article↗