Biomedical subjects

J Shiea

Publications and source records attributed to J Shiea.

7 recordsLinked to original sources

PubMed2001

Generating multiply charged protein ions by ultrasonic nebulization/multiple channel-electrospray ionization mass spectrometry.

An ultrasonic nebulization/multiple channel electrospray ionization (USN/MC-ES) source, which generates multiply charged peptides and proteins ions, was developed. The source is an ultrasonic nebulizer that is connected to a multiple channel electrospray ionization source. Aerosols were formed by ultrasonically nebulizing the sample solution. The aerosols were then purged into the central channel of a seven-channel ES source via nitrogen gas. A methanol solution that contained 1% trifluroacetic acid was electrosprayed through the outlying six electrosprayers. Detection of multiply charged peptide and protein ions indicated that electrospray was generated from the charged droplet containing analyte. The sample aerosol appeared to fuse with the charged methanol droplet in the air. Then electrospray ionization of the analyte occurred from the newly formed droplet. The peptide and protein prepared in deionized water were detected by this USN/MC-ES-MS. By varying the electrospray solvents, the signals of certain components in the mixture were selectively suppressed.

Aerosols↗

PubMed2001

8-Nitroxanthine, an adduct derived from 2'-deoxyguanosine or DNA reaction with nitryl chloride.

Activated phagocytic cells generate reactive nitrogen species, including nitryl chloride and peroxynitrite, for host defense against invading pathogens. It has been proposed that these reactive nitrogen species may cause DNA damage and thus contribute to the multistage carcinogenesis process associated with chronic infections and inflammation. Previous studies showed that peroxynitrite reacted with guanine, 2'-deoxyguanosine, or DNA forming 8-nitroguanine. We herein report formation of 8-nitroxanthine as the major nitration product in reactions of 2'-deoxyguanosine or calf thymus DNA with nitryl chloride produced by mixing nitrite with hypochlorous acid, and 8-nitroguanine was a minor product in these reactions. 8-Nitroxanthine was characterized by its NMR and laser desorption ionization mass spectra and by deamination of 8-nitroguanine. Formation of 8-nitroxanthine was also detected by xanthine reaction with various reactive nitrogen species, including nitryl chloride, peroxynitrite, nitronium tetrafluoroborate, and heated nitric and nitrous acid. The identity of 8-nitroxanthine in nitryl chloride-treated dG and DNA was confirmed by co-injection with synthetic 8-nitroxanthine and by its reduction to 8-aminoxanthine. Levels of 8-nitroxanthine and 8-nitroguanine in these reactions were quantified by reversed-phase HPLC with photodiode array detection. Once formed, 8-nitroxanthine was spontaneously removed from DNA with a half-life of 2 h at 37 degrees C and pH 7.4. Therefore, 8-nitroxanthine might be an important DNA lesion derived from reactive nitrogen species in vivo.

Chromatography, High Pressure Liquid↗

PubMed2000

A multiple channel electrospray source used to detect highly reactive ketenes from a flow pyrolyzer

This work detects protonated molecular ions of highly reactive pyrolytic products--cyclopentadienylideneketene, cyclohexadienylideneketenimine, and acetylketene--using a flow pyrolyzer connected to a multiple-channel electrospray mass spectrometry. The ketene generated in the flow pyrolyzer is directly conducted into the central channel of a seven-channel electrospray ionization source by a stream of nitrogen gas. Concurrently, a methanol solution containing 0.1% trifluoroacetic acid is electrosprayed through the outside six channels. The protonated methanol ions and the charged droplets generated from the outside six electrospray channels facilitate the ionization of the neutral ketenes through ion-molecule reactions or absorption followed by protonation.

Journal Article↗

PubMed2000

Rapid determination of trace nitrophenolic organics in water by combining solid-phase extraction with surface-assisted laser desorption/ionization time-of-flight mass spectrometry.

A rapid technique for the screening of trace compounds in water by combining solid-phase extraction (SPE) with activated carbon surface-assisted laser desorption/ionization (SALDI) time-of-flight mass spectrometry is demonstrated. Activated carbon is used both as the sorbent in SPE and as the solid in the SALDI matrix system. This eliminates the need for an SPE elution process. After the analytes have been adsorbed on the surfaces of the activated carbon during SPE extraction, the activated carbon is directly mixed with the SALDI liquid and mass spectrometric analysis is performed. Trace phenolic compounds in water were used to demonstrate the effectiveness of the method. The detection limit for these compounds is in the ppb to ppt range.

Microchemistry↗

PubMed2000

Generation of electrospray from a solution predeposited on optical fibers coiled with a platinum wire.

This study examines the feasibility of generating electrospray directly from the tip of two optical fibers bound together with Teflon tape. This approach does not require a capillary and syringe pump. The electrospray source is simply constructed by coiling the two optical fibers with a platinum (Pt) wire. The optical fibers extend beyond the Pt coil for approximately 1 cm. The sample solution is predeposited on the Pt coil by a micropipette. As the high voltage required for electrospray is applied to the coil, the sample solution moves along the grooves between the two optical fibers. A stable electrospray is subsequently generated at the tip of the fibers. The mass spectra of insulin, lysozyme, and ubiquitin are exactly the same as those obtained by conventional electrospray using a capillary and syringe pump. Rapid determination of the active ingredient in a tablet by this technique is demonstrated.

Fiber Optic Technology↗

PubMed1999

Rapid screening for diuretic doping agents in urine by C60-assisted laser-desorption-ionization-time-of-flight mass spectrometry.

This study describes a matrix-assisted laser-desorption-ionization (MALDI) mass spectrometry for rapid screening of 12 diuretics in spiked urine. C60 is used as the matrix for MALDI. Diuretics are directly analyzed by C60-MALDI without previous derivatization. The fact that most diuretic molecules contain sulfate groups accounts for why anions of the molecules can be easily desorbed and ionized in MALDI. Using C60 as the matrix is advantageous because of the low background in the low mass range on the negative MALDI mass spectrum. A clear mass window between m/z 200 and 600 in negative ion mode is also obtained. Only a minimum amount of the sample (< 1 microL) is necessary to perform the analysis. The detection limit of diuretics is approximately 0.1-1 microg/mL.

Benzothiadiazines↗

PubMed1998

Thin-layer chromatography-mass spectrometry using activated carbon, surface-assisted laser desorption/ionization.

The analysis of compounds separated by thin-layer chromatography (TLC) by surface-assisted laser desorption ionization (SALDI) mass spectrometry has been demonstrated. The compounds are analyzed from the surface of the intact TLC plate, and the preparation of the TLC plate is rapid and robust: the gel surface is covered with 2 microns activated carbon particles, and glycerol is added. Analytes diffuse from the interior of the gel to the surface where they are adsorbed onto the activated carbon. A nitrogen laser is used to desorb analyte ions from the carbon particles in a time-of-flight mass spectrometer. A wide range of organic compounds, including peptides, can be detected, either as protonated or as cationized molecules. Interference with "matrix peaks" is limited since background TLC-SALDI mass spectra typically show only a few intense peaks at low mass. The detection limit for bradykinin from a developed plate is approximately 25 ng (calculated for S/N = 3). The mass resolution (FWHM) varied from a high of about 500 to a low of about 100. This variability was likely due to surface charging. Methods to improve both mass resolution and sensitivity of TLC-SALDI are suggested.

Bradykinin↗