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  • 1
    Electronic Resource
    Electronic Resource
    Direct observation of a DNA quadruplex by electrospray ionization mass spectrometry (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 22 (1993), S. 181-183 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In 10 mM sodium phosphate, pH 7.6, containing 0.1 mM ethylenediaminetetraacetic acid, ions corresponding to the non-covalent, four-stranded oligonucleotide, d(CGCG4GCG)4, were detected by negative ion electrospray ionization (ESI) mass spectrometry at a low nozzle-skimmer (ΔNS) bias (-150 V), but not at a higher ΔNS bias (〉 -250 V). In contrast, when the sample was desalted and analyzed by ESI mass spectrometry at a low ΔNS bias only ions for the single-stranded d(CGCG4GCG) species were observed. These data agree with spectroscopic evidence which showed that oligonucleotides with the sequence motif 5′d(CGCGnGCG)3′, where n = 2-5, formed stable four-stranded complexes in the presence of monatomic cations, like K+, Ca2+, Na+ and Li+, but not in their absence.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200220307
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  • 2
    Electronic Resource
    Electronic Resource
    Reduced elution speed detection for capillary electrophoresis/mass spectrometry (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 57-62 
    Details
    ISSN: 1040-7685
    Keywords: capillary electrophoresis ; electrospray ionization ; mass spectrometry ; reduced field strength ; peptides ; proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A combined capillary electrophoresis/mass spectrometry (CE/MS) method is described that provides an increase in the efficiency of analysis by decreasing the analyte elution rate into an electrospray ionization (ESI) interface. The method is readily implemented by instituting a step change in the CE electric field strength for desired periods of time during a separation. As a result, the m/z range or the number of times an m/z range can be scanned while a solute elutes is increased by a factor proportional to the decrease in CE electric field strength. In addition, the method is shown not to cause any significant loss in separation quality as demonstrated for mixtures of proteins and peptides, while providing an effective gain in sensitivity. This allows an enhancement in the quality of mass spectra recorded while scanning wide m/z ranges. Mass spectra for a set of standard proteins were obtained for injections of 60 femtomole/protein, while analysis of an albumin tryptic digest was obtained for injections corresponding to 40 femtomoles of protein.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mcs.1220050109
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  • 3
    Electronic Resource
    Electronic Resource
    Use of small-diameter capillaries for increasing peptide and protein detection sensitivity in capillary electrophoresis-mass spectrometry (1993)
    Weinheim : Wiley-Blackwell
    Electrophoresis 14 (1993), S. 448-457 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The use of small ID capillaries is shown to provide a substantial increase in sensitivity for capillary electrophoresis-electrospray ionization/mass spectrometry (CE-ESI/MS). In a comparison using capillaries ranging from either 100 to 10 μm or 50 to 5 μm ID and chemically modified with aminopropylsilane, a 25- to 50-fold increase in sensitivity was observed for both peptide and protein mixtures. This enhanced solute sensitivity allowed the detection of approximately 150 attomoles of melittin (2845 Da) with selected ion monitoring and 600 attomoles of carbonic anhydrase (29157 Da) while scanning for CE-MS with a quadrupole mass spectrometer. For the protein mixture, mass spectra of sufficient quality for precise molecular weight determination (≤ 0.05%) were obtained for 600 attomole injections using a 5 μm ID capillary. The increase in sensitivity with small capillary diameters can be primarily attributed to a reduced mass flow rate of buffer and other background constituents into the electrospray source, which allows for greater sample ionization efficiency. A model that qualitatively accounts for the results is presented, but quantitative agreement is precluded due to difficulties in accounting for contributions due to a liquid sheath flow used with the electrospray source. The model accounts for the observation that the ESI/MS appears to function as a concentration-sensitive detector under many conditions using large-diameter capillaries. A transition occurs, however, to a regime where the ESI/MS functions as a mass flow-sensitive detector for small-diameter capillaries, where the ESI current is limited by the rate of delivery to the ESI source of charge carrying species in solution. These results suggest peptide and protein analysis at low attomole and subattomole levels should be obtainable with alternative types of mass spectrometers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150140170
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