Fourier transform mass spectrometry.

Fourier transform mass spectrometry will play an important role in the future because of its unique combination of high mass resolution, high upper mass limit, and multichannel advantage. These features have already found application in gas chromatography-mass spectrometry, multiphoton ionization, laser desorption, and secondary ion mass spectrometry. However, its most notable feature is the ability to store ions. This characteristic, when combined with the others, will allow expeditious study of the interaction of gas-phase ions with both photons (photodissociation) and neutral molecules, and the convenient application of this fundamental information for chemical analysis.

High pressure trapping in Fourier transform mass spectrometry: A radiofrequency-only-mode event.

A new event for the Fourier transform mass spectrometry (FTMS) sequence is developed and demonstrated. During this event, called a radiofrequency (RF)-only mode event, the typical passive cubic trap of a Fourier transform mass spectrometer is made to operate as an active quadrupole ion trap. The transition between active and passive modes is developed so that ion loss as a consequence of the transition can be held to 15% or less. The adduct of the ion-molecule reaction of the 1,3-butadiene radical cation and methyl vinyl ether was detected during the Rf-only-mode event at a helium pressure of ∼1×10(-3) torr even though this adduct is not detectable under standard FTMS operating conditions.

A gated trapping strategy with a two-time constant and a delay for catching in-field generated ions that range over three decades in mass-to-charge and two decades in velocity in Fourier-transform mass spectrometry.

In-field, matrix-assisted laser desorption/ionization (MALDI) may provide a means to keep part of the original promise of Fourier-transform mass spectrometry (FTMS) to give high performance and versatile mass spectrometry from a mechanically simple instrument. Gated trapping has been employed as a means of catching MALDI-produced ions in the FTMS trap. This approach is important for both in-field and externally produced ions. Even with improvements, gated trapping has not yet been able to catch ions over wide ranges of mass-to-charge and velocity. A design of a "two-time constant with a delay" gated trapping strategy using "idealized" potentials in a normalized system is given as an example to establish that in principle gated trapping strategies can capture ions that range over three decades of m/z and two decades in velocity. A procedure for calculating a physical system from the normalized system is given. The design is tolerant of variations in the physical parameters used to define the physical system from the normalized system.

A mechanism for poor high mass performance in fourier transform mass spectrometry.

The discovery of a mass-dependent electrical mechanism for signal loss of high mass ions in Fourier transform mass spectrometry is reported. Theoretical calculations and experimental evidence show the existence of resonances involving the z-motion and radial motion of the ion. The resonances are intrinsic in the cubic trap. This results in energy transfer between modes, expansion of the ion cloud, and a corresponding loss of signal. Quadrupolar trapping potential wells are proposed as a solution.

Ion cloud manipulation using the radiofrequency-only-mode as an improvement for high mass detection in fourier transform mass spectrometry.

It has been difficult to achieve the expected high resolving power for high-mass biomolecule ions in Fourier transform mass spectrometry. Our hypothesis is that ion clouds produced by laser desorption or injection are diffuse and produce poor signals. To test the hypothesis, clouds of benzene molecular ions produced by electron ionization were purposefully expanded via magnetron mode excitation and characterized by a new experimental sequence for cloud sectional analysis. The expanded cloud was then successfully focused to the trap center by using a high-pressure dynamic event (radiofrequency-only mode). The expanded cloud in a conventional cubic trap produces no detectable signal, whereas the focused cloud in a compensated trap yields a high-resolution signal with good signal-to-noise ratio.

A method for quantification from composite spectra: application to the determination of isomeric DNA photoproducts by tandem mass spectrometry.

Quantification of mixture components from their composite optical or mass spectra is a common need in analytical chemistry. We encountered the need when applying a combination of enzymatic digestion with nuclease P1 and tandem mass spectrometry to a mixture of isomeric photomodified oligodeoxynucleotides. In the procedure, we collisionally activated the [M - H]- or [M + Na - 2H]- ion of trinucleotide triphosphates, which were extricated enzymatically from the larger, damaged oligodeoxynucleotides, and we measured the relative abundances of characteristic fragment ions. The results sometimes yield curved calibrations for plots of the relative fragment ion abundances in the product ion spectra of isomers versus their relative amounts. We developed a normalized linear model, which brings understanding to the nonlinear plots and allows quantification of the mixture components from their composite spectra. The outcome demonstrates a general quantification procedure and shows that different yields for generating fragment ions from different constituents of the mixture cause the curved calibration lines.