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D E Goeringer

Publications and source records attributed to D E Goeringer.

9 recordsLinked to original sources
PubMed2003

"Fast excitation" CID in a quadrupole ion trap mass spectrometer.

Collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer is usually performed by applying a small amplitude excitation voltage at the same secular frequency as the ion of interest. Here we disclose studies examining the use of large amplitude voltage excitations (applied for short periods of time) to cause fragmentation of the ions of interest. This process has been examined using leucine enkephalin as the model compound and the motion of the ions within the ion trap simulated using ITSIM. The resulting fragmentation information obtained is identical with that observed by conventional resonance excitation CID. "Fast excitation" CID deposits (as determined by the intensity ratio of the a(4)/b(4) ion of leucine enkephalin) approximately the same amount of internal energy into an ion as conventional resonance excitation CID where the excitation signal is applied for much longer periods of time. The major difference between the two excitation techniques is the higher rate of excitation (gain in kinetic energy) between successive collisions with helium atoms with "fast excitation" CID as opposed to the conventional resonance excitation CID. With conventional resonance excitation CID ions fragment while the excitation voltage is still being applied whereas for "fast excitation" CID a higher proportion of the ions fragment in the ion cooling time following the excitation pulse. The fragmentation of the (M + 17H)(17+) of horse heart myoglobin is also shown to illustrate the application of "fast excitation" CID to proteins.

Animals↗
PubMed2000

Electrochemically modulated preconcentration and matrix elimination for organic analytes coupled on-line with electrospray mass spectrometry.

Demonstrated for the first time is the use of electrochemically modulated preconcentration and sample matrix elimination combined on-line with electrospray mass spectrometry (EMPM/ES-MS) for the enhanced analysis of organics by ES-MS. EMPM is similar to adsorptive stripping analysis. Accumulation of the targeted analytes at the working electrode of an on-line electrochemical flow cell is accomplished via a nonelectrolytic adsorption process that is controlled through the proper combination of the solvent system, the working electrode material, and applied potential. Once on the electrode, the analyte may be washed free of sample matrix components detrimental to mass spectrometric detection. The potential applied to the electrode during the detection step is chosen to release or strip the analytes unaltered back into the solvent stream for mass spectrometric detection rather than to oxidize or reduce them as would be the case for electrochemical detection. Thus, retention and elution of a target analyte with EMPM are controlled by switching the working electrode potential, rather than via a switch in mobile-phase composition, as is done in more traditional preconcentration and cleanup schemes used on-line with ES-MS. The proof-of-principle studies described here use the breast cancer drug tamoxifen and a metabolite, 4-hydroxytamoxifen, as the target analytes. A thin-layer, flow-by electrode cell with a glassy carbon working electrode is used as the preconcentration device. The nature of the working electrode, the solvent systems, and the electrode potentials necessary to accumulate and strip tamoxifen and 4-hydroxytamoxifen are discussed. Calibration curves were fitted using the Langmuir isotherm. Detection limits (DLs) using a 5.0 min preconcentration period with selected reaction monitoring for tamoxifen (m/z 372 --> 72) were bracketed as 0.010 nM < DL < 0.025 nM. The ability to simultaneously detect low nanomolar levels of both tamoxifen and 4-hydroxytamoxifen in pristine solution and 1/10 diluted urine is also demonstrated.

Electrochemistry↗
PubMed2000

Measurement of collision-induced dissociation rates for tantalum oxide ions in a quadrupole ion trap.

A study of factors influencing the collision-induced dissociation (CID) rate of strongly bound diatomic ions effected via resonance excitation in a quadrupole ion trap is presented. From these studies, an approach to measuring the CID rates is described wherein product ion recovery is optimized and the effect of competitive processes (e.g., parent ion ejection and product ion reactions) on rate measurements are prevented from influencing rate measurements. Tantalum oxide ions (dissociation energy = 8.2 eV), used as a model system, were formed via reactions of glow discharge generated Ta+ ions with residual gases in the ion trap. Neon (0.5 mtorr) was found to be a more favorable target gas for the dissociation of TaO+ than He and Ar, but collisional activation of TaO+ ions in neon during ion isolation by mass selective instability necessitated ion cooling prior to dissociation. A 25 ms delay time at qz = 0.2 allowed for kinetic cooling of stored TaO+ ions and enabled precise dissociation rate measurements to be made. CID of TaO+ was determined to be most efficient at qz = 0.67 (226 kHz for m/z 197). Suitable resonance excitation voltages and times ranged from 0.56 to 1.2 V(p-p) and 1 to 68 ms, respectively. Under these conditions, measurement of rates approaching 80 s(-1) for the dissociation of TaO+ could be made without significant complications associated with competing processes, such as ion ejection.

Journal Article↗
PubMed1996

Product ion charge state determination via ion/ion proton transfer reactions.

Proton transfer from protonated pyridine to product anions derived from quadrupole ion trap collisional activation of the triply charged anion of the oligonucleotide 5'-d(AAAA)-3' and the 6- charge state of oxidized bovine insulin A-chain is shown to be a rapid and effective way to determine product charge states. The reactions are carried out in a quadrupole ion trap as part of a procedure involving three stages of mass analysis. It is demonstrated that the reactions can be driven at rates sufficiently high to convert 30-80% of the initial product anion population to second generation products in 50-200 ms. The use of ion/ion reactions enjoys significant advantages over the use of ion/molecule proton transfer chemistry. For example, ion/ion reactions are more universal than ion/molecule reactions due to their greater exothermicity, and ion/ion reactions allow for precise control over the timing of introduction and ejection of each reactant. Despite the high exothermicity of the reactions, no significant fragmentation of product ions derived from high-mass multiply charged anions is observed.

Animals↗
PubMed1996

Cation attachment to multiply charged anions of oxidized bovine insulin A-chain.

Multiply charged anions of oxidized bovine insulin A-chain react with protonated quinoline exclusively by proton transfer in a Paul trap operated with helium bath gas at a pressure of 10(-3) Torr. The isomeric [C9H8N]+ ions formed from the reaction of [C4H4]+ with pyridine, on the other hand, react largely by attachment to the multiply charged anions of oxidized bovine insulin A-chain. This observation can be rationalized on the basis of competition between unimolecular decomposition versus cooling of the ion-ion collision complex. In the case of protonated quinoline, no significant barriers are expected along the reaction coordinate for proton transfer. However, the [C9H8N]+ ion-molecule reaction product is not expected to transfer a proton without undergoing rearrangement, as is consistent with ion trap collisional activation results. The rearrangement reaction introduces a significant barrier along the reaction coordinate, thereby increasing the lifetime of the ion-ion collision complex. RRKM modeling for a polypeptide of comparable size suggests that a barrier of 0.6 eV or greater will allow for the observation of cation attachment whereas the lifetimes of collision complexes with well depths less than approximately 0.6 eV are too short for collisional cooling by the bath gas to be effective.

Animals↗
PubMed1995

Ion/molecule reactions for improved effective mass resolution in electrospray mass spectrometry.

Tandem mass spectrometry is shown to improve the effective mass resolution in electrospray mass spectrometry. The technique involves selecting a population of ions within a narrow range of mass-to-charge values and allowing the ions to undergo proton transfer reactions. The shifts in mass-to-charge ratios associated with product ions formed by proton transfer allow for mass and charge assignment. The success of the technique relies on the relative enrichment of ions of a particular charge state that occurs in the mass-to-charge selection step. This approach can be used to extend the polymer mass range amenable to measurement, analyze mixtures that might otherwise be too complex for reliable mass measurements, and improve mass measurement precision when a mixture of cations is present within a given charge state. The technique is illustrated with a quadrupole ion trap using multiply-charged ions of cytochrome c, transfer ribonucleic acid from E. coli, strain W, and a synthetic deoxyribonucleic acid 30-mer.

Base Sequence↗
PubMed1994

Ion trap mass spectrometry. Using high-pressure ionization.

The quadrupole ion trap, operated with a relatively high-pressure bath gas, occupies a unique place among mass analyzers. As an ion storage device, it shares many characteristics with the ICR instrument, but the use of a light bath gas and mass-selective instability for mass analysis contrasts with normal ICR operation. The bath gas facilitates the capture of ions injected into the oscillating quadrupole field and cools the ions to the center of the ion trap before mass-selective ejection. The bath gas also provides a conduit for heating ions. Mild collisional activation conditions can dissociate clusters, such as solvated analyte ions, formed by ES. Dissociation of covalently bound ions can be used to obtain structural information as part of a tandem MS experiment or to destroy polyatomic species in elemental analyses. The moderate background pressure requirements of the ion trap using mass-selective instability make it a natural mass analyzer to be coupled with high-pressure ionization methods. The ion trap can provide a significant advantage in efficiency over beam-type mass spectrometers, which translates into lower detection limits. Lower detection limits can be realized from superior duty cycle and MS/MS efficiency, although transmission for single-stage MS is comparable. The greatest advantage in efficiency can be obtained with weak ion beams that require long ion accumulation times and therefore high duty cycles. This, in part, makes the ion trap particularly attractive for ES. Bright ion sources can provide similar advantages if major ion beam components can be ejected during ion accumulation to minimize the deleterious effects caused by ion-ion interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Mass Spectrometry↗
PubMed1992

Collisional activation with random noise in ion trap mass spectrometry.

Random noise applied to the end caps of a quadrupole ion trap is shown to be an effective means for the collisional activation of trapped ions independent of mass/charge ratio and number of ions. This technique is compared and contrasted with conventional single-frequency collisional activation for the molecular ion of N,N-dimethylaniline, protonated cocaine, the molecular anion of 2,4,6-trinitrotoluene, and doubly pronated neuromedin U-8. Collisional activation with noise tends to produce more extensive fragmentation than the conventional approach due to the fact that product ions are also kinetically excited in the noise experiment. The efficiency of the noise experiment in producing detectable product ions relative to the conventional approach ranges from being equivalent to being a factor of 3 less efficient. Furthermore, discrimination against low mass/charge product ions is apparent in the data from multiply charged biomolecules. Nevertheless, collisional activation with random noise provides a very simple means for overcoming problems associated with the dependence of single-frequency collisional activation on mass/charge ratio and the number of ions in the ion trap.

Amino Acid Sequence↗