Biomedical subjects

M S Westphall

Publications and source records attributed to M S Westphall.

5 recordsLinked to original sources

PubMed2001

A cylindrical capacitor ionization source: droplet generation and controlled charge reduction for mass spectrometry.

A cylindrical capacitor ionization source was used in conjunction with corona discharge charge reduction for generation of singly charged ions for mass spectrometric analysis. The source consists of a fused-silica capillary threaded with a platinum wire and placed inside a stainless steel tube. Application of an electric potential to the wire results in the production of a linear stream of charged droplets when an aqueous solution is pumped through the capillary. Subsequent solvent evaporation yields ions, providing a continuous ion source for mass spectrometry. Passage of the ions through a corona discharge charge reduction chamber permits reduction of the charge state to predominantly singly charged species, facilitating analysis of DNA and protein mixtures. The change from production of multiply charged ions to production of singly charged ions is extremely simple, requiring only modulation of the voltage applied to the corona discharge electrode. A simple technique for construction of the ionization source is reported.

Animals↗

PubMed2000

Corona discharge in charge reduction electrospray mass spectrometry.

Corona discharge is applied to charge reduction electrospray mass spectrometry for the analysis of complex mixtures of biological molecules. Recent work has described a method of charge reduction (reducing the charge states of analyte ions generated by the electrospray process) employing the radioactive isotope 210Po to produce neutralizing species. A variation to this approach is presented, in which charge neutralization is mediated by ions produced in a corona discharge. Varying the corona discharge voltage controls the current and the degree of charge reduction, providing predominantly singly charged ions that are detected by a commercial electrospray time-of-flight mass spectrometer. This technique provides charge reduction for the simplification of ESI spectra, without need for any radioactive material.

Cytochrome c Group↗

PubMed2000

Charge reduction electrospray mass spectrometry.

A new mass spectrometric technique, charge reduction electrospray mass spectrometry (CREMS), allowing the analysis of complex mixtures of biological molecules is described. The charge state of ions produced by electrospray ionization may be reduced in a controlled manner to yield predominantly singly charged ions through reactions with bipolar (i.e., both positively and negatively charged) ions generated using a 210Po alpha particle source. The electrospray-generated multiply charged ions undergo charge reduction in a "neutralization chamber" positioned before the entrance nozzle to the mass spectrometer. The ions are detected using a commercial orthogonal electrospray time-of-flight mass spectrometer, although the neutralization chamber can be adapted to virtually any mass analyzer. The CREMS results obtained exhibit a signal intensity drop-off with increasing oligonucleotide size similar to that observed with matrix-assisted laser desorption/ionization mass spectrometry. Proton-transfer reactions were found to be responsible for reducing charge on proteins and oligonucleotides in both positive and negative ion mode.

DNA↗

PubMed1999

Controlling charge states of large ions.

The charge state of ions produced in electrospray ionization (ESI) was reduced in a controlled manner to yield predominantly singly charged species by exposure of the aerosol to a bipolar ionizing gas. Analysis of the resulting ions on an orthogonal time-of-flight mass spectrometer yielded mass spectra greatly simplified compared with conventional ESI spectra. The decreased spectral complexity afforded by the charge reduction facilitates the analysis of mixtures by ESI mass spectrometry.

Aerosols↗

PubMed1996

Automatic matrix determination in four dye fluorescence-based DNA sequencing.

The four dye fluorescence detection strategy is a widely used approach to automated DNA sequence analysis. An important aspect of data processing in this approach is the multicomponent analysis to deduce the concentrations of four fluorophores from fluorescence emission intensities at four different wavelengths. This requires knowledge of the correct transformation matrix M. The matrix M is a function both of the fluorophores employed and the fluorescence detection system. M is typically determined either by a calibration process with individual dyes, or by choosing four well-separated individual peaks corresponding to the four different dyes. Both are time-consuming and complicated procedures for routine use. An automatic scheme for finding M directly from raw sequence data is presented here. This facilitates data analysis and the underlying algorithm may also find utility in other multispectral applications.

Algorithms↗