Biomedical subjects

Weidong Qin

Publications and source records attributed to Weidong Qin.

9 recordsLinked to original sources

PubMed2005

Combination of cationic surfactant-assisted solid-phase extraction with field-amplified sample stacking for highly sensitive analysis of chlorinated acid herbicides by capillary zone electrophoresis.

This report describes a novel online field-amplified sample stacking (FASS) procedure to analyze 16 chlorinated acid herbicides. By using a poly(vinyl alcohol) (PVA)-coated capillary to reduce electroosmotic flow and introducing a methanol-water plug before sample loading, the sample injection time could be very long without loss of sample and separation efficiency. Under the optimized condition, the FASS procedure could provide great sensitivity enhancement (5000-10 000-fold) and satisfactory reproducibility (relative standard deviations of migration times less than 2.4%, relative standard deviations of peak areas less than 8.0%). Combined with cationic surfactant-assisted solid-phase extraction (CSA-SPE), the limit of detection of the herbicides ranged from 0.269 to 20.3 ppt, which are two orders lower than those of the US Environmental Protection Agency standard method 515.1. The CSA-SPE-FASS-CE method was successfully applied to the analysis of local pond water.

2-Hydroxypropyl-beta-cyclodextrin↗

PubMed2005

Portable capillary electrophoresis system with potential gradient detection for separation of DNA fragments.

A portable capillary electrophoresis (CE) system with a novel potential gradient detection (PGD) was utilized to separate DNA fragments. For the first time it was demonstrated that separation of DNA fragments in polymer solution could be detected by a portable CE system integrated with PGD, with a limit of detection (LOD) comparable to that of the CE-ultraviolet (UV) method. Effects of buffer solution, sieving medium, and applied voltage were also investigated. The portable CE-PGD system shows several potential advantages, such as simplicity, cost effectiveness, and miniaturization.

Bacteriophage phi X 174↗

PubMed2004

Determination of ammonium and metal ions by capillary electrophoresis-potential gradient detection using ionic liquid as background electrolyte and covalent coating reagent.

A capillary zone electrophoresis (CZE)-potential gradient detection (PGD) method coupled with field-amplified sample injection was developed to determine alkali metal, alkaline-earth metal, nickel, lead and ammonium ions. The capillary surface was coated with dialkylimidazolium-based ionic liquid and thus the electroosmotic flow (EOF) of the capillary was reversed. The buffer composed of 7.5 mM lactic acid, 0.6 mM 18-crown-6, 12 mM alpha-cyclodextrin (alpha-CD); it was adjusted to pH 4.0 by 1-hexyl-3-methylimidazolium hydroxide. The 11 cations were baseline separated within 14 min with 5.1-18.9 x 10(4) plates (for 40-cm-long capillary) in separation efficiency, and the detection limits were in the range of 0.27-7.3 ng/ml. The method showed good reproducibility in terms of migration time with RSD < or = 0.90% for run-to-run and < or = 1.65 for day-to-day assessment.

Buffers↗

PubMed2003

1,3-dialkylimidazolium-based room-temperature ionic liquids as background electrolyte and coating material in aqueous capillary electrophoresis.

The 1-ethyl-3-methylimidazolium (EMIM) cation was found to have constant mobility of 4.5 x 10(-4) cm2 V(-1) s(-1) over the pH range of 3 to 11. The electroosmotic flow of bare silica capillary was reversed by the covalently bonded room-temperature ionic liquid (RTIL) coating. With run buffer of 5 mM EMIM (pH 8.5), NH4+ in human urine was separated from the K+ matrix and was detected to be 0.37 +/- 0.012%. K+, Na+, Li+, Ca2+, Mg2+ and Ba2+ were baseline separated in RTIL-coated capillary with run buffer of 10 mM EMIMOH-acetic acid at pH 5, and the concentration of the above ions in a red wine were detected to be 907, 27.9, 0, 71.0, 83.4 and 31.1 microg/ml, respectively. The RTIL-coated capillary showed stable electroosmotic flow for at least 80 h in the run buffer.

Electrolytes↗

PubMed2003

Determination of chlorophenoxy acid herbicides by capillary electrophoresis with integrated potential gradient detection.

This report describes separation and detection of chlorophenoxy acid herbicides spiked in drinking water by the technique combining solid-phase extraction, field-amplified sample stacking, capillary electrophoresis, and potential gradient detection. The herbicide solution (400 mL) was concentrated to 0.1 mL by the solid-phase extraction procedure. The buffer containing 3 mM ammonia and 0.3 mM hydroxypropyl-beta-cyclodextrin was adjusted to pH 9.0 with ammonia. The sample solution was injected into the capillary to 30% of the whole length, and -9 kV and 9 kV were employed for field-amplified sample stacking and separation, respectively. The herbicides were baseline separated and the detection limits with the above combined techniques were in the range of 1-4 x 10(-2) ng/mL.

Buffers↗

PubMed2003

Electrophoresis of DNA in ionic liquid coated capillary.

An ionic liquid (IL) coated capillary was prepared and investigated for DNA separation. The electroosmotic flow of the capillary was reversed between pH 4.5 and 9. Below 900 base pairs the larger DNA fragment suffered more retardation in the IL coated capillary due to the increasing charge density of the fragment with size. In the presence of 4% hydroxyethylcellulose, the phiX174 DNA-Hae III digest fragments were baseline separated in both IL- and polyacrylamide-coated capillary except for the fragments of 271 and 281 base pairs; while the analysis time was shorter in the IL-coated capillary. Our experiments indicated that the IL-coated capillary could work stably in the run buffer for at least 96 h with no notable deterioration in performance.

Animals↗

PubMed2002

An ionic liquid coating for determination of sildenafil and UK-103,320 in human serum by capillary zone electrophoresis-ion trap mass spectrometry.

Ionic liquid (IL) was covalently bonded onto the silica capillary surface and the electroosmotic flow was reversed over a pH range of 3.5 to 7. Sildenafil (SL) and its metabolite UK-103,320 (UK) in human serum were detected by solid-phase extraction followed by capillary zone electrophoresis-mass spectrometry analysis. The running buffer contained 10 mM acetic acid adjusted to pH 4.5 with 1 M ammonia, and the separating voltage was set to -25 kV. The adsorption of the analytes onto the bare capillary wall was eliminated by the IL coating and the drugs were baseline-separated within 14 min with detection limits (S/N = 3) of 14 and 17 ng/mL for SL and UK, respectively. The method developed showed good intraday precision in terms of relative standard deviation (RSD) with respect to migration time (RSD </= 0.76%, n = 5) and peak area (RSD </= 3.4%, n = 5); the relative coefficients of linear regression for both targets were better than 0.99 within linear dynamic range (SL: 50-600 ng/mL; UK: 40-400 ng/mL). Satisfactory interday precision was obtained with respect to the slope of the regression (RSD </= 4.21%, n = 9) and the migration time (RSD </= 1.1%, n = 9). The IL coating could be used with stable electroosmotic flow (RSD = 2.78%, n = 10) for at least 80 h.

Alkylation↗

PubMed2002

Separation of ionic liquid cations and related imidazole derivatives by alpha-cyclodextrin modified capillary zone electrophoresis.

The separation and detection of 1-alkyl-3-methylimidazolium, including isomers, and related imidazole derivatives was performed by alpha-cyclodextrin (alpha-CD) modified capillary zone electrophoresis. The separations were carried out in a running buffer comprising 5.0 mM triethylamine and 2.0 mM alpha-CD adjusted to pH 4.5 by acetic acid. All the analytes were baseline separated within 8 min and the detection limits (signal-to-noise ratio = 3) ranged between 0.42 and 1.36 ppm. The method showed good linearity (within 3-50 times the detection limits, r > 0.99) and reproducibility (relative standard deviation < 0.8% for migration times and < 3% for peak areas), which should make it suitable for routine analysis. It was employed in detecting impurities in commercial chemicals, and 0.27% 1-methylimidazole in 1-ethyl-3-methylimidazolium chloride and 0.55% imidazole in 2-ethylimidazole were found. In addition, it was employed in process analysis during synthesis of ionic liquids and demonstrated a potential to provide information on the reaction mechanism.

Cations↗

PubMed2002

Determination of acidic herbicides in surface water by solid-phase extraction followed by capillary zone electrophoresis.

A rapid solid-phase extraction-capillary zone electrophoresis (CZE) method for determining 2,4-dichlorophenoxyacetic acid, 4-(2,4-dichlorophenoxy) butyric acid, and 2,4,5-trichlorophenoxyacetic acid in real water samples is described. Factors affecting the recoveries and detection of the targets are investigated. With samples being acidified to pH 2 and salted by sodium sulfate to 2% (w/w), an average recovery of greater than 85% is obtained using ethyl acetate as the eluent on an octadecylsilane-bonded silica cartridge. A running buffer of 5 mM sodium tetraborate in a water-acetonitrile mixture (70:30, v/v) adjusted to pH 9 is employed in the CZE analysis, and the targets can be analyzed within 7 min with good reproducibility and acceptable sensitivity. The method is suitable for detecting herbicide residues of sub-parts-per-billion levels in surface water. A local pond water is analyzed, and the concentrations of 2,4-dichlorophenoxyacetic acid and 4-(2,4-dichlorophenoxy) butyric acid are detected to be 0.27 +/- 0.03 ppb and 0.61 +/- 0.08 ppb, respectively.

Acids↗