Biomedical subjects

G A Valaskovic

Publications and source records attributed to G A Valaskovic.

4 recordsLinked to original sources

PubMed1996

Attomole protein characterization by capillary electrophoresis-mass spectrometry.

Electrospray ionization with an ultralow flow rate (</=4 nanoliters per minute) was used to directly couple capillary electrophoresis with tandem mass spectrometry for the analysis and identification of biomolecules in mixtures. A Fourier transform mass spectrometer provided full spectra (>30 kilodaltons) at a resolving power of approximately 60,000 for injections of 0.7 x 10(-18) to 3 x 10(-18) mole of 8- to 29-kilodalton proteins with errors of <1 dalton in molecular mass. Using a crude isolate from human blood, a value of 28,780.6 daltons (calculated, 28,780.4 daltons) was measured for carbonic anhydrase, representing 1 percent by weight of the protein in a single red blood cell. Dissociation of molecular ions from 9 x 10(-18) mole of carbonic anhydrase gave nine sequence-specific fragment ions, more data than required for unique retrieval of this enzyme from the protein database.

Animals↗

PubMed1996

Sampling error in small-bore sheathless capillary electrophoresis/electrospray-ionization mass spectrometry.

Two previously unreported sources of systematic error in electrokinetic injection caused by induced (hydrodynamic) flow in sheathless capillary electrophoresis/electrospray have been characterized for an interface constructed from 5 microns i.d. capillary column(s) with a 2-5 microns i.d. electrospray tip(s). The tip of a sheathless interface is usually exposed to the atmosphere, resulting in evaporation of buffer solvent and inducing flow inside the column; such flow can cause a significant underestimation of injection size for quantitative electrokinetic sampling by as much as 50%. This bias can be eliminated during the injection process by temporarily immersing the tip in buffer solvent. The second source of hydrodynamic flow results from the electrostatic pull exerted by the electrospray process on the buffer, reducing migration times. Reduction in migration times causes an overestimation of sampling volume if there are no electrospray processes during the sampling event. The magnitude of this effect is a complex function of electrophoretic and electrospray parameters and has been measured to be as high as 15% for 5 microns i.d. capillaries. The possible deterioration of electrophoretic resolution caused by these processes is not yet clarified.

Animals↗

PubMed1995

Attomole-sensitivity electrospray source for large-molecule mass spectrometry.

Full mass spectra of high resolving power are obtained from 0.2 nL sample volumes of large (> 10 kDa) nucleotides and proteins using a new electrospray ionization (ESI) system combined with Fourier transform mass spectrometry. The ESI needles are fabricated by laser-heated pulling of fused-silica tubing (5-20 microns i.d.), followed by chemical etching and surface metalization. Total analyte loaded at the instrument of 8.6 fmol and 216 amol produces signal-to-noise ratios of 400:1 and 60:1, respectively, and resolving power of > 10(5) for full mass spectra, while the total amount of material consumed is approximately 150 and 10 amol, respectively.

Animals↗

PubMed1992

Quantitative imaging ion microscopy: a short review.

A short review of recent efforts being made in the quantification of images in ion microscopy is given. Special aspects of instrumentation, detection and acquisition, which are unique to direct imaging secondary ion mass spectrometry, are discussed in relation to the successful application of traditional empirical quantification schemes. Application of such quantification schemes requires proper sample preparation, standardization, analysis, and quite often, special techniques in image processing and the correlation of ion microscopy with other microscopies. Quantification within this technique is a difficult goal which can only be realized if the analyst pays strict attention to every step of the analytical process.

Animals↗