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Biomedical subjects

C M Whitehouse

Publications and source records attributed to C M Whitehouse.

7 recordsLinked to original sources
PubMed1994

LC/ESI-MS determination of proteins using conventional liquid chromatography and ultrasonically assisted electrospray.

Conventional unassisted electrospray ionization mass spectrometry (ESI-MS) has severe limitations as a liquid chromatography (LC) interface due to the few solvent compositions which can be electrosprayed without some type of assistance. LC mobile phases which have high flow rates (over 5 microL/min), high conductivity, or high surface tension are normally unsuitable for use with ESI. For this reason, an ultrasonic nebulizer has been developed which mechanically creates the fine spray of droplets needed for ESI and thus functions independently of the solvent composition. This device also operates at considerably higher liquid flow rates, up to several hundred microliters per minute. To characterize the system's performance, the ultrasonic nebulizer frequency, source electrode potentials, and drying and focusing gas flow rates were studied and optimized. Also, droplet size measurements were taken using a phase-Doppler anemometer, which showed consistent nebulizer performance up to a liquid flow rate of several hundred microliters per minute. Finally, the ultrasonic nebulizer was used for an LC application involving the separation of proteins on 1.0 and 2.1 mm i.d. columns. LC flow rates of up to 200 microL/min of mobile phases containing 0.1% trifluoroacetic acid could be easily nebulized. With the 1.0 mm i.d. column, as little as 32 fmol of cytochrome c could be detected in selected ion monitoring mode.

Chromatography, Liquid↗
PubMed1994

Ultrasonically assisted electrospray ionization for LC/MS determination of nucleosides from a transfer RNA digest.

The use of an ultrasonic nebulizer to assist electrospray ionization mass spectrometry (ESI-MS) has been described and demonstrated with the analysis of a transfer RNA digest by microcolumn LC. The restricted range of mobile-phase compositions amenable to the electrospray process has traditionally placed a severe limitation on the types of LC applications that can be used with ESI-MS. For this reason, an ultrasonic nebulizer configured for LC has been developed that can generate the fine dispersion of liquid required for ESI-MS from any type of mobile phase. In the case presented here, a transfer RNA was enzymatically digested into its substituent nucleosides, which were then analyzed by microcolumn LC. The required mobile-phase gradient (beginning at 5% methanol) falls outside the solvent range that can be used with conventional electrospray. The ultrasonic nebulizer, however, resolves this problem. The fundamental behavior of the four most common nucleosides (cytidine, adenosine, guanosine, uridine) was studied, and conclusions concerning the effects of solution chemistry were drawn. Specifically, signal from the H+ adducts of these species seems to be strongly dependent on the pKa value. Also, effects from several source operating variables were examined. These included capillary exit voltage, drying and focusing gases, and nebulizer frequency. Performance was found to be consistent over a wide range (0-100% methanol) of mobile-phase compositions. The limit of detection for adenosine injected onto a microcolumn was found to be 100 amol. Finally, nucleosides from as little as 150 fmol of RNA (amount prior to digestion) could be detected.

Chromatography, Liquid↗
PubMed1992

Time-of-flight mass spectrometry with an electrospray ion beam.

An electrospray ionization source has been coupled to a reflection time-of-flight mass spectrometer. By orienting the ion source perpendicular to the field-free drift region, the longitudinal energy spread of the ion packet has been substantially reduced, allowing a mass resolving power of over 1000 to be achieved for both low-mass and high-mass ions of biological interest. In addition, instrument sensitivity allows the routine detection of low-picomole and subpicomole quantities of large multiply charged species such as cytochrome c (MW = 12,360.9). The potential utility of this instrument for conducting rapid screening of chromatographic effluents is discussed in light of its simplicity, rapid scanning speed, and high sensitivity.

Mass Spectrometry↗
PubMed1991

An ion-storage time-of-flight mass spectrometer for analysis of electrospray ions.

A preliminary design and implementation of a novel approach to electrospray-mass spectrometry are described. Based on a time-of-flight mass analysis, the instrument provides several important advantages for on-line mass analysis: 1, simplicity, ease of use and low manufacturing cost; 2, rapid scan speed, yielding quasi-instantaneous full mass scans at repetition rates up to several kHz; 3, soft ionization and accurate mass determination of extremely large analyte molecules; 4, high sensitivity.

Arginine↗
PubMed1989

Electrospray ionization for mass spectrometry of large biomolecules.

Electrospray ionization has recently emerged as a powerful technique for producing intact ions in vacuo from large and complex species in solution. To an extent greater than has previously been possible with the more familiar "soft" ionization methods, this technique makes the power and elegance of mass spectrometric analysis applicable to the large and fragile polar molecules that play such vital roles in biological systems. The distinguishing features of electrospray spectra for large molecules are coherent sequences of peaks whose component ions are multiply charged, the ions of each peak differing by one charge from those of adjacent neighbors in the sequence. Spectra have been obtained for biopolymers including oligonucleotides and proteins, the latter having molecular weights up to 130,000, with as yet no evidence of an upper limit.

Ions↗